Metal halide perovskites have transformed the landscape of solution-processable semiconductors, especially for photovoltaics, light emission, and radiation detection. Their success arises from an unusual combination of strong optical absorption, long carrier lifetimes, defect tolerance, compositional flexibility, and low-temperature processability. However, the same structural softness and compositional tunability that make perovskites powerful also introduce persistent challenges, including phase instability, ion migration, moisture sensitivity, and light-induced halide segregation in wide-bandgap mixed-halide absorbers.

In this presentation, we will discuss how the broader structural chemistry of perovskite-derived materials opens new opportunities beyond the conventional corner-sharing ABX₃ perovskite framework. Particular emphasis will be placed on perovskitoids, a structurally related class of metal halides that retain some corner-sharing octahedral connectivity but also incorporate edge- or face-sharing octahedra.

This mixed connectivity provides an additional design parameter, beyond composition and dimensionality, for controlling bandgap, charge transport, luminescence, and stability. Compared with conventional perovskites, perovskitoids offer a much broader structural landscape and can access bandgaps that would otherwise require halide alloying or dimensional reduction. In favorable cases, this enables wide-bandgap pure-iodide absorbers with improved photostability, avoiding the halide-segregation problem that limits mixed-halide perovskites in tandem solar cells.

Colloidal semiconductor nanocrystals that are active in the infrared spectral region are being intensively investigated as solution-processable inexpensive materials for future consumer market products. Together with lead sulfide, indium arsenide (InAs) nanocrystals are probably the most studied ones. This talk will discuss the advances of our group in the synthesis and characterization of InAs nanocrystals and their exploitation in lighting applications. The first part will focus on the use of green precursors and new reducing agents. I will also present our recent findings on the influence of ligands on the formation of organic/inorganic impurities that can compromise the cleaning of the nanocrystals and how this can be avoided. The role of metal halides as additives in reducing the density of defects/traps and in promoting a shell growth will be also presented. Finally, I will discuss the parameters that lead to strong light emission in core/shell nanocrystals, and their exploitation in light emitting devices.

Two-dimensional (2D) halide perovskites have emerged as a versatile platform for tunable optoelectronic materials, owing to their layered crystal structure and chemical flexibility. In these materials, organic spacer ligands separate the inorganic perovskite layers and play a central role in governing structural rigidity, charge transport, and light emission. Understanding how spacer chemistry influences excited-state processes is therefore essential for rational materials design.

In this talk, I will present a comparative study of manganese (Mn)-doped 2D perovskites incorporating either aromatic phenethylammonium (PEA) or aliphatic butylammonium (BA) spacer ligands. Mn doping provides a robust route to achieving strong, broadband luminescence, yet the interplay between dopant emission, exciton transport, and spacer identity remains poorly understood. By systematically varying Mn concentration and sample morphology, from nanoplatelets to bulk crystals, we uncover distinct doping regimes, including edge-localized Mn incorporation at high doping levels and uniform dopant distribution at lower concentrations.

Despite similar Mn incorporation behavior, the two spacers lead to markedly different optical responses. PEA-based perovskites exhibit significantly stronger Mn-related emission than their BA-based counterparts. Using transient reflection microscopy, we directly probe exciton transport and find nearly a twofold enhancement in exciton diffusivity for PEA systems. These differences are correlated with crystal rigidity and exciton–phonon coupling.

Overall, this work highlights how organic spacer ligands control both charge mobility and luminescence in 2D perovskites, offering design principles for next-generation light-emitting materials.

Lead halide perovskites offer great potential for optoelectronics and quantum technologies. Understanding their fundamental optical and spin properties is key to advancing these applications.

Using low-temperature magneto-optical spectroscopy on single perovskite nanocrystals, we fully resolve their band-edge exciton fine structure and reveal how exciton level ordering depends on composition. Across various compounds, we establish universal scaling laws linking exciton fine structure splitting, trion and biexciton binding energies to band-edge exciton energy.

Remarkably, methylammonium lead halide perovskite nanocrystals (MAPbX₃, X = Br, I) nanocrystals deviate from these universal trends. Their low-temperature magneto-optical spectra display distinct excitonic signatures that point to inversion-symmetry breaking and the emergence of a Rashba effect. We propose that the low-temperature ordering of the permanent methylammonium dipoles generates an internal electric polarization, providing the microscopic origin of this behavior and fundamentally modifying the excitonic fine structure.

Colloidal InAs/ZnSe quantum dots (QDs) are promising heavy-metal-free emitters for near- and short-wave infrared optoelectronics. However, their implementation in light-emitting diodes (LEDs) has been limited by challenges in synthesis and losses in conventional device configurations. In 2024, we reported near-infrared LEDs emitting at 900 nm with an external quantum efficiency (EQE) of 13.3%, enabled by effective surface passivation of InAs QDs synthesized using an amino-As precursor[1]. We subsequently extended this platform to the short-wave infrared by employing a seeded-growth synthesis, achieving tunable electroluminescence from 1007 to 1410 nm and peak EQEs up to 6.20%, representing the first efficient InAs QD-LEDs emitting beyond 1100 nm[2]. Most recently, we established a seedless synthetic route to large InAs nanocrystals with ZnSe shelling, yielding photoluminescence tunable from 1000 to 1500 nm and providing the material foundation for infrared-emitting devices[3]. Building on this progress, we used a novel LED configuration to reduce device losses and improve EQE in this spectral range.

The growing demand for quantum technologies in communication and computing necessitates the development of novel quantum light sources, driving a constant search for model systems satisfying the stringent requirements for a coherent single-photon source. Colloidal lead halide perovskite nanocrystals (LHP NCs) in the weak confinement regime have recently emerged as compelling candidates, demonstrating high single-photon purity, sub-100 ps radiative lifetimes, and photon indistinguishability of 56% – among the highest reported for any colloidal single-photon emitter. [1,2] To date, however, only CsPbBr₃ NCs in the 20-25 nm size range have been investigated, whereas NCs beyond this size regime remain largely unexplored, leaving open a fundamental question: can single-photon purity be retained in larger NCs while simultaneously pushing radiative lifetimes to their ultimate limits?

In this study, we demonstrate the synthesis of CsPbBr₃ NCs with dimensions exceeding 30 nm through the rational design of growth-mediating ligands that preserve NC colloidal stability during synthesis. By systematically leveraging the structure of ligand tail, we extend this approach to all cuboidal shapes – cubes, plates, rods – with exquisite control over all three morphological parameters. Post-synthetic ligand exchange with state-of-the-art phosphoethanolamine-based zwitterionic ligands enhances NC emissivity and imparts robust colloidal, environmental, and dilution stability – important prerequisites for optical characterization of individual NCs. Systematic single-particle spectroscopy reveals how NC dimensions govern key metrics of single-photon emission – radiative lifetime, photon antibunching, and polarized emission – thereby identifying the size regime of CsPbBr₃ NCs optimal for quantum emitter applications.

Chemical engineering of heterostructure colloidal QDs has given rise to an unprecedented class of emissive materials for optoelectronic applications like photovoltaics, display and solid-state lighting. Although InP-based QDs show excellent performance in the green and red regions, it is highly challenging to access the blue range of 440-460 nm. The latter is technologically of utmost importance, in particular for the production of blue QD light-emitting diodes (QLEDs), which are required to realise electroluminescent pixels for next generation display technologies showing enhanced performance and reduced power consumption.

Chalcopyrite-type I-III-VI₂ QDs emerged in the past 15 years as an alternative class of QD materials providing combined composition- and size-tuneable optical and electronic properties and opening up a novel space of compounds beyond well-established binary semiconductors. In particular CuInS₂ and AgInS₂ QDs have been studied most widely due to their efficient luminescence and possibility to synthesise them both in organic medium or in the aqueous phase. Changing the trivalent metal from In³⁺ to Ga³⁺ gives access to larger bandgap energies and hence allows for blue-shifting the emission peak. Although these QDs can show a decent PLQY, their broad PL line width due to an emission mechanism involving intra-bandgap trap states has been recognised as the major issue impeding their utilization in display applications, as these require narrowband emission to achieve a wide colour gamut. One way to reduce the line width is via the passivation of the surface with III₂-VI₃ shells such as Ga₂S₃ or In₂S₃ instead of ubiquitously used ZnS.

Here, we present the synthesis of AgGaS₂/Ga₂S₃ (AGS/GS) core-shell QDs exhibiting narrow band-edge emission in the blue range around 450 nm [1]. Unexpectedly, we found that Ga₂S₃ itself can act as an efficient deep-blue emitter when overcoated with appropriate shell materials [2]. Finally, we will present our latest results on high-entropy alloyed halide perovskite nanocrystals, which upon functionalisation with zwitterionic ligands yield narrow blue emission with close-to-unity quantum yield and excellent photostability.

Low-dimensional metal halide perovskites exhibit rich excitonic physics arising from strong carrier–phonon coupling, exciton localization, and self-trapping processes. These unique characteristics lead to excited-state dynamics that differ fundamentally from those of conventional free-exciton semiconductors, involving complex pathways of energy relaxation, recombination, and energy transfer. Understanding and controlling these excitonic processes is essential for the development of next-generation light-emitting materials and devices.

In this presentation, I will discuss our recent efforts to understand exciton dynamics in low-dimensional metal halides using ultrafast spectroscopic techniques. We reveal that localized excitons establish a rapid thermodynamic equilibrium with trap states in Mn²⁺-doped perovskite nanomaterials. Rather than acting solely as non-radiative loss channels, these trap states function as efficient intermediates for host-to-dopant energy transfer, accelerating Mn²⁺ excitation by more than an order of magnitude. More importantly, the trap states serve as exciton reservoirs that enable unusual emission behaviors, including persistent afterglow, anti-thermal quenching, and suppression of concentration quenching at high dopant concentrations.

Beyond understanding exciton dynamics, recent efforts have focused on actively manipulating excitonic processes on ultrafast timescales using advanced pump-push-probe spectroscopic approaches. Through selective perturbation of excited-state populations and energy-transfer pathways, exciton relaxation and emission processes can be dynamically regulated, providing new opportunities for controlling energy flow in low-dimensional perovskites. These studies highlight how a fundamental understanding of exciton dynamics can be translated into strategies for engineering and manipulating light-emission processes, opening new directions for advanced photonic and optoelectronic applications.

Copper(I) halide-based emitters have recently garnered significant attention for their potential in X-ray imaging applications owing to their efficient emission, facile synthesis and low toxicity.[1-3] While several strategies have been proposed to improve scintillation efficiency in these systems,[4-6] the critical role of Cu–I cores—particularly during ultrafast energy conversion and transport—has received limited attention. In this work, we introduce a unified ligand strategy to construct a series of zero-dimensional copper(I) iodide clusters, including a Cu1I1 monomer, Cu2I2 rhomboid dimer, and Cu4I4 cubane tetramer, all exhibiting near-unity photoluminescence quantum yield (𝜙PL). This approach enables a systematic investigation of how core architecture governs radioluminescence (RL) behavior and efficiency beyond 𝜙PL. Our results demonstrate that the core geometry has a strong influence on both thermal stability and exciton relaxation pathways. Notably, low-temperature PL–RL differences uncover a previously unrecognized exciton relaxation channel intrinsic to the Cu4I4 cubane cluster, allowing a fraction of excitons to directly populate the ³CC state. This process confines exciton generation, transport, and radiative recombination within the Cu–I cubane, thereby potentially increasing the exciton transfer efficiency and enhancing scintillation efficiency. These findings provide critical insights into the fundamental scintillation mechanisms and structure–property relationships of Cu–I clusters, establishing core geometry as a key design principle for the development of next-generation, high-performance scintillators.

The magnetic van der Waals (vdW) materials offers a platform to explore fundamental magnetism at the atomic limit. Transition metal phosphorus trisulfides (MPX₃) family have emerged as a keystone two-dimensional (2D) magnetic platform, possessing intrinsic ferromagnetic or antiferromagnetic properties, that persist down to a few- or a monolayer form. Within the MPX₃ family, FePS₃ and NiPS₃ are the dominant examples demonstrating variable types of magnetism. FePS₃ has an Ising-type antiferromagnetism (T_N ~ 118K) with out-of-plane anisotropy. NiPS₃ represents an XY-type (T_N ~ 155K) system, where spins are confined to the ab-plane. These layered systems can be isolated and reassembled into vertical heterostructures (HRs) combining members from the same family or with others (e.g., hBN, transition metal dichalcogenide). Such heterostructures provide a versatile platform for tailoring electronic, optical, and magnetic properties via proximity effects at their interfaces.

This lecture will demonstrate two most recent investigations (yet unpublished). The first example comprises NiPS₃/WSe₂ composition, prepared via dry exfoliation and stacking methodologies (including hBN capping), explored by low-temperature micro-photoluminescence (μ-PL) and magneto-PL spectroscopy. The heterostructures exhibit multiple sharp excitonic peaks emerging from localized intralayer WSe₂ excitons confined by interface-induced moiré patterns local strain. Notably, these excitons exhibit spontaneous circular polarization even in the absence of an external magnetic field, as well as nonlinear Zeeman split, signifying a magnetic proximity effect imparted by the antiferromagnetic NiPS₃ layer. Density functional theory (DFT) calculations confirmed that the PL exposed interfacial hybridization and spin texture modifications emanate from a proximity effect.

The second example describes a combination between CuCrPS₃ Fello-electric/magnetic compounds or the MnPS₃ ferrootroids with WSe₂ emitter. The ferroic layers bestow magneto-electric coupling, hence permitting manipulation of the magnetism both by magnetic and electric fields. Further on, the optical emission of the adjacent WSe₂, indirectly is tunned by the changes occurring upon a proximity effect.  Hence a single photon source manipulation upon demand can be feasible.  The lecture will include the motivation and preliminary results.

Metal halide perovskites are highly promising emitters owing to their narrow and compositionally tunable photoluminescence, high absorption coefficients and defect-tolerant optoelectronic behaviour. However, achieving controlled crystallization together with long-term environmental stability remains a major challenge. Here, we report a vapour-assisted strategy for the in-situ formation of highly emissive metal halide perovskite nanocrystals embedded within hydrated metal-acetate matrices.

The nanocomposite films are fabricated from solution and activated through exposure to controlled water vapour or carboxylic-acid vapours. These vapours act as chemical triggers that regulate ion mobility, precursor dissolution–reprecipitation processes and local matrix coordination. This enables the conversion of low-dimensional, weakly emissive perovskite-related phases into confined three-dimensional perovskite nanocrystals with intense and spectrally narrow photoluminescence.

The acetate matrix plays a multifunctional role as a physical confining medium, ionic reservoir and chemical regulator of the crystallization process. By varying the perovskite composition, metal-acetate host and vapour chemistry, the emission can be tuned throughout the visible region. In particular, Ni(OAc)₂-based matrices enable the formation of strongly emissive CsPbBr₃, MAPbBr₃ and FAPbBr₃ nanocomposites. Longer-chain carboxylic-acid vapours further modify the local coordination environment and reduce water uptake, offering an effective route to improve the environmental robustness of the films.

This vapour-activated nanocomposite approach provides a low-temperature and scalable route to produce stable perovskite emitters without conventional ligand-engineering steps. The resulting materials are promising for down-conversion coatings, light-emitting diodes, displays, photonic devices and other emerging light-emitting technologies.

Silver sulfide (Ag₂S) nanocrystals are promising candidates as fluorescence markers, because they show emission at 1200 nm, and the emission intensity strongly changes with temperature. Hence, the fluorescence of these particles could be used to probe the temperature inside biological cells. To explore the fluorescence mechanisms, we combined synthetic studies with optical investigations on ensembles and performed single particle fluorescence spectroscopy.

The fluorescence properties of these emerging light emitting materials reveal many novel phenomena such as a decrease of the fluorescence intensity by 90 % if the temperature is increased from 10 to 50 °C.  Additionally, the fluorescence intensity is partially quenched upon illumination and reversibly recovers within seconds. Two distinct fluorescence lifetime components in the 1 ns and 100 ns range hint to different recombination channels, and first measurements if single particle spectroscopy show pronounced fluorescence intermittency.

Here we show how the fluorescence properties are depending on different surface modifications such as molecular and ionic surface treatments. Finally, we suggest a model for the fluorescence mechanism in silver sulfide nanocrystals.

Metal-halide perovskites have recently emerged as a promising platform for ultrafast scintillators owing to their high light yield and short emission lifetimes [1]. Our recent advances in in the field have demonstrated that coupling perovskite scintillators with plasmonic nanoantennas enables Purcell-enhanced radiative recombination, leading to brighter and faster scintillation, while subsequent studies extended these concepts toward exciton–plasmon strong coupling in bulk nanoplasmonic scintillators [2-4]. Building upon these developments, we investigate whether the geometry of plasmonic nanostructures can itself serve as a design parameter governing the transition from enhanced spontaneous emission to coherent light–matter interactions in different classes of perovskite scintillators.

To address this question, two representative perovskite emitters exhibiting distinct electronic structures, CsPbBr₃ and CsCu₂I₃, were co-dispersed with shape-controlled gold nanoparticles within a polymer matrix to form a composite slab. Gold octahedra and rhombic dodecahedra with sizes ranging from 40 to 90 nm were synthesized and further characterized spectroscopically and structurally. Their localized surface plasmon resonances were continuously tuned between 450 and 650 nm, enabling systematic control over the spectral overlap between plasmonic and excitonic transitions. The optical response was investigated using steady-state photoluminescence (PL), time-resolved PL (TRPL) allowing direct correlation between plasmonic resonance conditions and scintillation dynamics.

For CsPbBr₃ composites, rhombic dodecahedral Au nanoparticles with plasmon resonance centred at 545 nm induced the strongest impact on emission dynamics. At room temperature, nearly ninefold acceleration of the PL decay demonstrates highly efficient plasmon-assisted radiative rate engineering. Upon cooling below 180 K, where excitonic dephasing is significantly reduced, the system evolves into the strong-coupling regime, giving rise to pronounced Rabi splitting accompanied by a 2.5-fold enhancement of the PL intensity [3-4]. Simultaneously, the emission lifetime increases by approximately six times relative to room temperature, reflecting modified exciton relaxation dynamics associated with the formation of hybrid exciton–plasmon states.

In contrast, CsCu₂I₃ exhibits a distinctly different coupling behaviour despite being investigated within the same plasmonic platform. Strong exciton–plasmon coupling is observed exclusively for octahedral Au nanoparticles when their localized surface plasmon resonance spectrally coincides with the broadband emission centred near 600 nm. Under these resonance conditions, a pronounced Rabi splitting is accompanied by an approximately 2.5-fold enhancement of the PL intensity. Rhombic dodecahedra of comparable dimensions do not exhibit splitting despite similar spectral tuning, demonstrating that spectral overlap alone is insufficient to induce coherent coupling. We attribute this behaviour to the geometry-dependent electromagnetic near-field distribution, where the sharp edges of octahedral nanoparticles generate highly localized plasmonic hot spots, substantially strengthening the local optical field and exciton–plasmon interaction [5].

We demonstrate that the evolution from Purcell-enhanced emission to coherent exciton–plasmon coupling is governed not only by spectral resonance but also by the geometry of plasmonic nanostructures and the intrinsic properties of the emitting material. Our findings establish shape-selective plasmonic engineering as a new design principle for perovskite scintillators for future of ultrafast, high-light-yield detectors.

Low-dimensional (LD) organic metal halide hybrids (OMHHs) have emerged as a highly versatile class of solution-processable light-emitting materials with exceptional structural and optical tunability. Through rational selection of organic cations and metal halide building blocks, their dimensionality can be precisely controlled at the molecular level to form zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) structures, providing a powerful platform for tailoring electronic structures, exciton dynamics, and light-emission properties. Unlike conventional metal halide perovskites, the rich organic-inorganic chemistry of LD OMHHs enables emissions to originate from either the organic cations or the metal halide components, depending on their relative energy alignment. Consequently, emission colors can be continuously tuned across the entire visible spectrum, exhibiting either narrow-band or broadband luminescence with photoluminescence quantum efficiencies approaching unity. Furthermore, the radiative decay lifetimes can be engineered over an exceptionally broad range, from nanoseconds for organic-cation-centered fluorescence to microseconds and milliseconds for metal-halide-centered phosphorescence and self-trapped exciton emission. In this talk, I will present our recent advances in the molecular design, synthetic control, and photophysical understanding of luminescent LD OMHHs. By engineering organic-inorganic interactions, crystal packing, and excited-state processes, we achieve precise control over emission color, bandwidth, lifetime, and efficiency while establishing fundamental structure-property relationships. I will also discuss recent developments in chiral LD OMHHs exhibiting circularly polarized luminescence, as well as strategies for integrating these materials into high-performance optoelectronic devices, such as light-emitting diodes and radiation scintillators.

Near-infrared (NIR) spectral detector have emerged as key components of next-generation wearable healthcare systems, enabling continuous, non-invasive monitoring of vital physiological signals.[1] Cd- and Pb-based chalcogenide quantum dots (QDs) exhibit excellent tunable optical properties in this spectral region, but their commercialisation is restricted by toxicity and environmental regulations. Among RoHS (Restriction of Hazardous Substances) certified safer alternatives, especially InP, a III-V QD system stands tall in this spectral region.[2] Conventional hot-injection synthesis typically produces zinc-blende InP QDs, which often suffer from poor size control and result in a broader spectrum in the NIR region.[3] In contrast, wurtzite InP (w-InP) QDs prepared by cationic exchange of Cu_3-xP QDs, followed by extraction of copper impurities, show much better control over particle size and enable a tunable optical response upto NIR spectral region (~810 nm) by changing the size of the QDs.[4] Moreover, due to spin-orbit and crystal-field splitting, w-InP QDs show multiple absorption peaks, which can be utilised for multi-purpose bioelectronic applications.[5] Conventional photodetectors require an external energy source for better sensitivity but are less portable and suffer from power dissipation. Therefore, in this work, we introduced large-sized w-InP QDs (average diameter ~12 nm) for the first time in a self-powered photodetector, enabling multispectral detection around the NIR spectral region. This designed self-powered detector can be portable and well compatible with cutting-edge optoelectronic devices, and it can also address the energy crisis with the highest priority by operating without any external bias.[6] The electron transporting layer (ETL, ZnO) and w-InP QDs were spin-coated subsequently on a conductive indium tin oxide (ITO)-coated glass substrate, followed by evaporation of the hole transporting layer (HTL, MoO₃) and metal electrode (Au) to form a layer-by-layer structured self-powered detector. The fabricated devices exhibited multispectral photodetection with spectral detectivity peaks around the NIR spectral region, at ~820 nm, ~790 nm and ~725 nm, measured at zero external bias. Then we systematically investigated the influence of different ultrathin (a few nm) metal interlayers evaporated between QDs and the HTL layer on the overall optoelectronic characteristics of the self-powered device. Systematic comparison of different metal interlayers reveals that the interfacial electronic structure can be effectively tailored to enhance the charge transfer process. Among the investigated metals, Ti demonstrated the most significant improvement in device performance by promoting efficient carrier extraction without compromising the self-powered characteristics. Notably, after introducing Ti-metal as an interlayer (w-InP/Ti), nearly a threefold (~3-fold) increase in external quantum efficiency (EQE) was observed under NIR light, whereas specific detectivity lies in the range of ~3–8 × 10¹¹ Jones in NIR to visible-red light region. Furthermore, the w-InP/Ti device detected very weak 800 nm NIR light (~4.16 μW cm^-2) while operating at 0 V bias, highlighting its capability for highly sensitive light detection, which can be suitable for sophisticated health monitoring devices. In addition, the Ti interface passivated the surface defects, which enabled faster charge extraction and sped up the detector response by nearly two (~2) times. Therefore, it can be concluded that by combining interface engineering with metals and w-InP QDs, we demonstrated a high-performance, self powered photodetector capable of sensitive multispectral detection around NIR region. This approach offers a scalable pathway for III-V QDs utilisation towards next-generation, energy efficient and environmentally friendly optoelectronic devices.

Lead-free halide double perovskites have attracted considerable attention as environmentally benign alternatives to conventional lead-based perovskite semiconductors for photonic and optoelectronic applications. Their enhanced chemical stability, structural versatility, and compositional flexibility make them promising candidates for light-emitting devices, photodetectors, and integrated photonic components [1]. In particular, layered double perovskites exhibit strong quantum confinement and enhanced excitonic effects arising from their quasi-two-dimensional crystal structure, providing an attractive platform for tailoring light–matter interactions. However, effective strategies for engineering their electronic structure and optical properties remain relatively unexplored.

Here, we investigate heterovalent cation alloying as an approach to bandgap engineering in lead-free layered double perovskites. Sn-alloyed Ag–Bi-based layered double perovskite microcrystals were synthesized over a broad range of alloy compositions by partially substituting Bi³⁺ with Sn²⁺. Structural, optical, and vibrational characterization was performed to elucidate the influence of heterovalent alloying on the crystal lattice and electronic structure. Particular attention was paid to the evolution of the optical absorption edge and the corresponding bandgap as a function of Sn content.

The alloyed materials exhibit a pronounced composition-dependent evolution of their optical properties. Optical absorption measurements reveal a systematic red shift of the absorption edge with increasing Sn incorporation at intermediate alloying levels, corresponding to a significant narrowing of the optical bandgap. This behavior indicates that heterovalent substitution induces substantial modification of the electronic states rather than a simple interpolation between the parent compounds. In addition to bandgap tuning, incorporation of Sn²⁺ is expected to influence lattice distortions and vibrational properties, further affecting carrier relaxation and energy transfer processes within the material.

These results demonstrate that heterovalent cation alloying provides an effective route for continuously tuning the electronic structure of layered double perovskites. The observed composition-dependent bandgap modulation highlights the potential of this material platform for designing lead-free perovskites with tailored optical responses and controllable light–matter interactions. Such tunability makes Sn-alloyed layered double perovskites promising candidates for next-generation photonic and optoelectronic technologies [2–4].

The presentation will the concept of lattice-matching well-known for the epitaxy of bulk semiconductors and how it was adapted to halide perovskites adding in the mechanical free energy expansion a linear-quadratic coupling between strain and octahedra rotations (Kepenekian, Nano letters 2018). The usefulness of this approach will be demonstrated through a few experimental examples related to the lattice parameter variations in 2D multilayered perovskites, the 2D/3D matched or mismatched thick bilayer heterostructures, the nano-inclusions of 2D perovskites in 3D matrices or buried quantum dots of 3D perovskites in a 3D matrix.  The presentation will review additional theoretical results considering the influence of polymorphism on the electronic structure, the electron-phonon coupling or the surface in halide perovskites.  The presentation will show of tuning transferable atomistic parameters in DFTB codes, based on an approximation to density functional theory, provide a pathway to atomistic calculations of the optoelectronic properties of halide perovskites including low dimensional structures and heterostructures.    

After the seminal work of Pringsheim¹ on a fluorescent gas (Na vapor) in 1929, substantial progress has also been made in laser cooling of bulk solid-state matter via phonon-mediated photoluminescence upconversion, chiefly in rare-earth-doped crystals and semiconductors^{2, 3, 4, 5, 6, 7}. However, extending laser cooling to individual solid-state quantum emitters, key building blocks for diverse quantum photonics applications, has remained elusive due to the twin challenge of preserving near-unity photoluminescence quantum yield at the single-particle level and effectively suppressing thermal backflow from the environment. Here, we experimentally demonstrate individual QDs with near-unity quantum yield cool reversibly and rapidly (< 1 s) upon sub-bandgap laser excitation, as inferred from redshifted, spectrally narrowed photoluminescence and accelerated radiative decay. Atomistic and continuum heat-transport simulations identify the organic ligand shell as an efficient thermal barrier, allowing the QD core to be cooled to several tens of K below its environment. This work establishes laser cooling at the single-emitter level and promises a scalable pathway to cryogen-free, narrowband, and coherent solid-state quantum-light sources.

Colloidal III–V semiconductor nanocrystals have emerged as promising materials for infrared optoelectronics owing to their size-tunable electronic structures and solution-processability. Despite significant progress in recent years, establishing a clear relationship between synthetic chemistry and the resulting electronic properties remains a central challenge because of the highly covalent nature of III–V bonding and the complexity of their reaction pathways and surface structures.

In this presentation, I will discuss our recent efforts to understand how reaction chemistry influences the structural and electronic characteristics of colloidal III–V semiconductor nanocrystals. I will first introduce mechanistic studies on precursor conversion and reaction pathways that provide new insights into the formation of III–V nanocrystals. I will then present recent observations on shape-defined InAs quantum dots, highlighting how synthetic control over crystal morphology offers opportunities to investigate electronic structures beyond conventional quantum-confinement considerations. Finally, I will briefly discuss how these advances contribute to infrared optoelectronic functionalities in III–V nanocrystal solids.

Rather than providing a comprehensive picture, this presentation aims to highlight several emerging questions regarding the interplay among reaction chemistry, crystal structure, surface characteristics, and electronic structure, and to discuss possible directions toward a more fundamental understanding of colloidal III–V semiconductor nanocrystals.

Solution-processed metal–halide perovskites are promising gain media for compact, wavelength-tunable, and low-cost coherent light sources due to their high absorption coefficients, strong photoluminescence, defect tolerance, and large optical gain. However, translating their intrinsic gain into stable, spectrally controlled, low-threshold lasing requires simultaneous optimization of the perovskite material quality and the optical cavity architecture. Here, we present a material–cavity co-design strategy for realizing low-threshold amplified spontaneous emission and cavity-mediated lasing from MDACl₂-passivated mixed-cation perovskite thin films integrated with lithographically defined glass nanopillar photonic crystal substrates.

The perovskite gain medium, based on Cs/FA lead iodide–bromide compositions with controlled MDACl₂ incorporation, was first optimized through steady-state absorption, photoluminescence, time-resolved photoluminescence, and femtosecond transient absorption spectroscopy. Moderate MDACl₂ passivation improves the optical quality of the films by reducing non-radiative recombination pathways and extending the carrier lifetime. The optimized 3% MDACl₂-doped film exhibits the most favorable gain behavior, with an amplified spontaneous emission threshold of approximately 2.4 µJ cm⁻², significantly lower than that of the undoped film. Femtosecond transient absorption measurements reveal the formation of broadband optical gain in the near-infrared spectral region, with the gain window emerging near the band edge and broadening with increasing excitation fluence. These ultrafast measurements directly link defect passivation, carrier relaxation, and gain formation, confirming the suitability of the optimized perovskite film as an efficient light-emitting gain medium.

To further reduce the lasing threshold and achieve spectral control, the optimized perovskite film was deposited onto periodically patterned SiO₂ nanopillar photonic crystal cavities fabricated by electron-beam lithography and dry etching. The nanopillar geometry was designed to provide strong spatial overlap between the optical cavity modes and the perovskite gain region. By tuning the lattice periodicity of the nanopillar arrays, the cavity resonance was systematically aligned with the perovskite gain spectrum. Room-temperature micro-photoluminescence measurements demonstrate narrowband, cavity-mediated stimulated emission with wavelength tunability across the near-infrared region. The nanopillar cavities reduce the emission threshold to approximately 0.7 µJ cm⁻², more than three times lower than that of the unpatterned optimized film, while narrowing the emission linewidth to approximately 3.3 nm. The emission wavelength shifts systematically with the nanopillar lattice period, confirming deterministic cavity control over the lasing mode.

These results demonstrate that defect-passivated perovskite thin films integrated with glass nanopillar photonic crystal cavities provide an effective platform for low-threshold, spectrally tunable, and solution-processable coherent light emission. The combination of ultrafast gain spectroscopy, compositional passivation, and scalable nanophotonic cavity engineering offers a promising pathway toward integrated perovskite lasers for on-chip photonics, optical communication, sensing, and emerging light-emitting technologies.

Metal halide perovskite nanocrystals (PNCs) are promising materials for next-generation optoelectronic applications owing to their high photoluminescence efficiency, tunable bandgaps, defect tolerance, and solution processability. However, several critical challenges remain, including the toxicity of lead, the oxidation instability of Sn²⁺, surface defect formation, insulating long-chain ligands, and intrinsic limitations in lead-free double perovskites.

This talk focuses on defect engineering and photophysical control in low-toxicity and lead-free perovskite nanocrystals, including Sn-based, Sn–Pb alloyed, and halide double-perovskite quantum dots. Through controlled doping, surface reconstruction, antioxidation strategies, and short-chain ligand engineering, we elucidate the key relationships among crystal structure, defect states, excited-state dynamics, and device performance[1-10].

In Sb³⁺/Mn²⁺ co-doped Cs₂NaInCl₆ QD inks, dual-ion doping combined with ligand shortening enables near-unity photoluminescence quantum yield, improved charge transport, suppressed nonradiative recombination, and enhanced LED performance[9]. For Sn-based and Sn–Pb alloyed PNCs, temperature-dependent spectroscopy, ultrafast measurements, STEM imaging, and theoretical calculations reveal the roles of static disorder, carrier–phonon coupling, antisite defects, and Sn oxidation in carrier trapping and recombination[6-8,10]. Furthermore, a synergistic antioxidation strategy using trioctylphosphine (TOP) and Sn powder effectively suppresses Sn(IV) formation, reduces defect-mediated trapping, and produces highly luminescent, phase-stable CsSnI₃ and Sn–Pb alloyed nanocrystals with prolonged carrier lifetimes[6].

Together, these results establish a versatile defect-engineering framework for low-toxicity and lead-free perovskite nanocrystals, providing important design principles for sustainable optoelectronic technologies, including LEDs, fluorescence thermometry, solar cells, and other advanced photonic devices.

Short-wave infrared (SWIR, 1000–2000 nm) light-emitting devices (LED) are of strong interest for applications in optical communications, biological imaging, and sensing [1]. Colloidal InAs-based quantum dots (CQDs) have emerged as a promising RoHS-compliant material system for SWIR optoelectronics, offering tunable emission and recent progress in both synthesis and device integration [2]. However, achieving simultaneously high efficiency, high radiance, and long-wavelength emission remains challenging due to non-radiative losses and suboptimal charge balance in device architectures. Previous InAs quantum dot light-emitting diodes have demonstrated SWIR emission [3], but efficiency and radiance at telecom wavelengths have remained limited.

Here, we report heavy-metal-free SWIR CQD-LEDs based on InAs/ZnSe core-shell CQDs integrated into optimized device architectures. An InAs CQD electron transport interlayer is used to suppress interfacial quenching and improve charge balance, while hole transport layer optimization via BCF-doped PTAA enhances charge injection and recombination rate. As a result, the devices achieve an external quantum efficiency up to 4.2%, a maximum radiance exceeding 10 W sr^-1 m^-2, and stable emission at 1525 nm. In addition, a long operational lifetime is obtained under ambient, non-encapsulated conditions.

Overall, this work demonstrates that combined emitter and device interface engineering enables efficient and bright heavy-metal-free SWIR CQD-LEDs operating in the telecom-relevant spectral range.

Field of Quantum dots has (QDs) been dominated by heavy metal based materials such CdSe, CdS, PbSe etc. However, they are toxic and should be replaced with more environment friendly materials. InP a III-V semiconductor which has a direct band gap, very low surface recombination velocity and excellent optical quality, is a strong contender for their replacement. Further, confining the material to 2D and 1D will be highly beneficial in its applications. However, the development of InP QDs has been impeded by several inherent challenges, including a high degree of covalency and the need for highly reactive precursors during synthesis. Synthesising two-dimensional (2D) III–V colloidal nanosheets remains a significant challenge due to the difficulties in controlling anisotropic growth and surface chemistry. Here we demonstrate colloidal synthesis of 2D and 1D InP nanostructures. Tuning the reaction temperature switches the growth from lateral 2D nanosheets to axial 1D nanowires, highlighting the thermodynamic and kinetic control over nanocrystal morphology. The resulting atomically flat nanosheets—measuring 2–5 monolayers thick with lateral dimensions of 20–80 nm—exhibit sharp, thickness-dependent excitonic absorption features with narrow linewidths below 80 meV. Post-synthetic surface passivation successfully eliminates oxide-related trap states, increasing the photoluminescence quantum yield from <5% to 25% while maintaining rapid radiative lifetimes.These results provide a deeper understanding of shape-controlled synthesis in covalent III–V materials, positioning InP nanostructures as a sustainable, cadmium-free platform for next-generation photonic applications.

Short-wave infrared (SWIR) light sources are key components of a wide range of optoelectronic sensing technologies, including machine vision and light detection and ranging (LiDAR). Conventional SWIR light-emitting diodes (LEDs) are typically based on single-crystal III–V semiconductors, most commonly In₁₋ₓGaₓAs grown on InP. However, the complex multi-step epitaxial growth and device-processing requirements associated with these materials have limited their broader integration into consumer electronics.

Colloidal quantum dots (QDs) offer a promising alternative platform for SWIR light emission.¹ These solution-processable nanomaterials can be synthesized at low cost, while their optical properties can be tuned through control of their size, shape, and composition. Their compatibility with established and inexpensive complementary metal–oxide–semiconductor (CMOS) technologies further makes them attractive for scalable optoelectronic applications.

Although red-, green-, and blue-emitting QDs have already achieved commercial success in display technologies, SWIR-emitting QDs have yet to enter the consumer market. A major challenge is achieving high-efficiency emission beyond 1100 nm while remaining compliant with the European Restriction of Hazardous Substances (RoHS) Directive. To date, state-of-the-art SWIR QD-LEDs have largely relied on toxic Pb- and Hg-based chalcogenide QDs, owing to their mature and well-established synthetic chemistry. By contrast, progress with indium arsenide (InAs) QDs has been constrained by the limited availability of suitable precursors, which has contributed to low photoluminescence quantum yields, broad size distributions, and electroluminescence typically restricted to wavelengths below 1100 nm.

In this talk, I will present our recent advances in the synthesis of InAs QDs using an amino-As precursor^2,3,4,5 and their integration into SWIR light-emitting diodes.^6,7,8 Particular emphasis will be placed on InAs/ZnSe core/shell QDs and the corresponding LED devices enabling electroluminescence beyond 1100 nm.

Metal halide perovskites have emerged as promising emitters for light-emitting diodes (LEDs) due to their easily tunable bandgap, narrow emission linewidth, and good charge carrier mobility.^[1] Perovskite LEDs with emission peaks in the visible and short-wavelength near-infrared regions (<920 nm) have recently achieved rapid increase in external quantum efficiency (EQE).^[2,3] In contrast, long-wavelength near-infrared perovskite LEDs, which offer distinct advantages in various applications such as night vision, biological tissue analysis, biomedical imaging, sensing and optical communications, are largely underdeveloped.

Environmentally friendly tin iodide perovskites, particularly cesium or cesium-rich tin iodide perovskites, have demonstrated intrinsic long-wavelength near-infrared emission (>920 nm).^[4] However, realizing high-efficiency LEDs based on these materials is highly challenging due to easy oxidation of Sn²⁺ and fast crystallization.^[5]

Here, we demonstrate a facile strategy that combines a low-temperature preheating step with an organic additive to precisely regulate grain and pinhole formation in cesium-rich tin iodide perovskite films. This approach not only suppresses Sn²⁺ oxidation but also enables fine-tunable optical structures within LED stacks, leading to enhancement of both photoluminescent quantum efficiency and light outcoupling efficiency. The resulting 960 nm-emitting LEDs achieve a high EQE of 9.5%, which is among the highest reported values in the long-wavelength near-infrared region (>920 nm). Our work not only offers a practical approach for enhancing the performance of tin iodide perovskites but also deepens the understanding of the relationship between film properties and LED performance.

Perovskite nanocrystals (PNCs) have recently attracted significant attention due to their excellent optoelectronic properties and potential applications in photovoltaics and advanced display technologies. However, increasing stability and mastering self-assembly are persistent challenges. Here, we explore a liquid crystal like ligands for PNCs as means to combat both issues: achieve assemblies with non trivial symmetry, and achieve necessary stability . These so called promesogenic ligands are organic compunds, designed and synthesized in our laboratory, comprising aromatic and alkyl parts.

First, I show covering PNCs with these ligands substantially improves their thermal stability. Namely, after coating PNCs can survive 120°C instead of 80°C. Then, going one step further I will present that temperature-induced changes in ligand conformation modulate interparticle distances and ordering within thin films. Inspired by our previous work on metallic nanoparticle- liquid crystal systems[1][2], where external stimuli enabled control over particle ordering and optical absorption, we extend this approach to perovskite nanocrystals. In contrast to plasmonic systems, where absorption dominates, here we aim to investigate how controlled ordering may influence emission properties.

In particular, such structural reorganization may create conditions conducive to collective emission phenomena, including superfluorescence, characterized by synchronized, intense emission bursts. The ability to control nanocrystal organization may also open pathways toward their integration into liquid crystalline matrices exhibiting helical ordering, which could serve as a platform for generating circularly polarized luminescence (CPL).

CsPbBr₃ nanocrystals functionalized with novel organic ligands were synthesized accordingly to established protocols[3], and characterized using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), UV–Vis spectroscopy, and fluorescence spectroscopy. These techniques allow us to correlate structural ordering with optical behavior and to confirm thermal stability.

This work aims to establish a foundation for designing stimuli-responsive perovskite nanocrystal assemblies, where controlled ordering serves as a tool to access and potentially tune emergent optical phenomena.

Indium phosphide (InP) quantum dots (QDs) are the premier heavy-metal-free alternatives to cadmium-based materials for optoelectronic application ranging from displays to quantum photonic technologies. While traditional hot-injection synthesis methods yield the isotropic zinc-blende phase, we developed a framework for wurtzite-phase InP (w-InP) to unlock structural anisotropy and superior near-infrared (NIR) performance. Our approach utilizes cation exchange from monodisperse hexagonal Cu_3-xP nanocrystal templates. A critical post-synthetic nitrosyl tetrafluoroborate treatment is employed to extract residual copper impurities and surface oxides. This transforms non-emissive cores into optoelectronic-grade material with resolved polarized excitonic features and tunable emission spanning 600–820 nm. We further advanced these systems through heteroepitaxial shell engineering using ZnSe/ZnS architectures achieving high photoluminescence quantum yields (PL QY). Moreover, advancements in shell and morphology control over III-V core/II-VI shell QDs and its effect on controlling the emission properties will be discussed.

Finally, we demonstrate the utility of w-InP QDs in photocatalytic hydrogen generation exploiting the deep red spectral region. To resolve the trade-off between catalytic overpotential and spectral harvesting, we introduce a "rainbow" compartment approach. By stacking different QD sizes to sequentially utilize high-energy then low-energy red photons, we maximize solar spectrum utilization and enhance conversion efficiency.

Collectively, this work establishes wurtzite InP as a high-performance platform for sustainable optoelectronics and energy technologies.

Lead halide perovskite nanocrystals (NCs) are promising materials for optically-pumped lasers operating in the visible range, owing to their exceptional optical gain properties and reduced non-radiative recombination losses arising from their defect-tolerant nature. In previous work of the group, it was shown that nanosecond-excited amplified spontaneous emission (ASE) can be optimized using the transparent biopolymer cellulose acetate (CA) as spacer layer to produce polymer–CsPbX₃ NC multilayer architectures. Additionally, experiments showed that such multilayers can be deposited in thin, free-standing membranes that exhibit improved ASE figures of merit due to more efficient optical confinement and waveguiding properties compared to multilayers deposited in conventional quartz substrates [1].

Herein, the methodology is extended towards thicker perovskite nanocrystal–polymer multilayers comprising up to 20-layer pairs on both rigid and flexible substrates. Photoluminescence (PL) and amplified spontaneous emission (ASE) are reproducibly optimized for different multilayer thicknesses namely thick 6–8 pairs and thin 2–3 pairs, respectively, reflecting the competing effects of optical confinement and photon recycling for PL, and increased reabsorption, scattering, Auger recombination for ASE. Free-standing CA membrane architectures further enhance optical confinement and reduce ASE thresholds compared to glass-supported structures across all multilayer thicknesses. Finally, preliminary "origami" architectures are realized by folding multilayer membranes to increase the optical interaction length without additional deposition, as a scalable approach towards devices such as luminescent solar concentrators and radiation scintillators.

For next-generation QD-based displays relying no longer on colour conversion (photoluminescence) but on electrically driven active pixels (electroluminescence), nanocrystals emitting in the three primary colours R,G,B are required. InP-based core/shell quantum dots represent a highly promising environmentally-benign alternative to Cd-based QDs for the green and red range.

However, achieving narrow emission in the blue range (460-480 nm) is highly challenging with this material because the InP QDs are in the strong quantum confinement regime, where small changes in diameter induce significant fluctuations in the bandgap. Here, we explore a novel synthetic scheme, giving access to ultrasmall (around 1.3 nm) InP core QDs and their overgrowth with a thick ZnS shell (8 monolayers) in a single step, leading to highly luminescent InP/ZnS QDs emitting around 470 nm, albeit with a comparably broad linewidth of 60 nm (FWHM). With the goal to reduce the latter, interfacial treatment with different zinc halides is performed, which results in a slight size increase from around 7 to 8 nm, lower size distribution and higher circularity of the particles.

In the case of ZnF2, a strongly enhanced excitonic peak at 434 nm with a peak-to-valley ratio rising from 1.2 to 1.8 is achieved, despite the fact that XPS analysis still reveals significant oxidation of the InP core, induced through side reactions of the zinc carboxylate precursor during the shell growth. Based on temperature-dependent PL studies in a 75-400 K range, we show that the influence of exciton-phonon coupling on the ensemble PL linewidth is negligible as compared to the broadening induced by the core QD size distribution. Finally, the potential of the obtained QDs for incorporation into QLED structures will be discussed.

In recent years, perovskites have emerged as promising candidates for next-generation scintillators [1] owing to their structural versatility, tunable electronic properties, and efficient radiative processes [2, 3]. While Pb-based systems have been extensively investigated [4], the optical and scintillation properties of Pb-free Ni-based layered perovskites remain largely underexplored. In this work, we present a comprehensive experimental and theoretical study of the Ni-based perovskite family (A)₂NiCl₄, where A = phenylmethylammonium (PMA), phenylethylammonium (PEA), and phenylpropylammonium (PPA).

High-quality single crystals were synthesized and structurally characterized by X-ray diffraction, confirming their layered crystal structure and excellent crystallinity. Their optical properties were investigated using photoacoustic spectroscopy, photoluminescence, and radioluminescence measurements, while density functional theory calculations were employed to elucidate the electronic structure. Two characteristic optical features were identified across the series: a high-energy emission centered at approximately 300 nm, attributed to ligand-surface-related states, and a broad band near 500 nm originating from Ni-derived d-states that define the electronic bandgap of these materials. The combined experimental and theoretical results demonstrate that both the inorganic [NiCl₄]^2- layers and the organic spacer cations govern the electronic structure and radiative recombination pathways.

Radioluminescence measurements reveal that (PPA)₂NiCl₄ exhibits the most promising scintillation performance, achieving a light yield of approximately 23,000 photons/MeV at 80 K [5]. The observed dependence of the optical response on the organic cation highlights the effectiveness of A-site engineering for tailoring the scintillation properties of layered hybrid perovskites. These findings establish Pb-free Ni-based perovskites as a promising platform for environmentally friendly low-temperature scintillators and provide new insights into the relationship between crystal structure, electronic states, and luminescence mechanisms in hybrid perovskite materials.

Metal halide perovskites, either in 2D, 3D or nanocrystal form, have emerged as leading materials for next-generation light-emitting technologies owing to their exceptional optoelectronic properties. However, their performance is strongly influenced by local structural disorder and finite-temperature effects, which are often overlooked in conventional crystalline descriptions [1]. In this contribution, we present a first-principles framework that explicitly incorporates anharmonic thermal fluctuations, electron-phonon coupling, and local symmetry breaking to investigate the electronic and optical properties of halide perovskites [2,3]. Our framework relies on the special displacement method that provides an efficient platform for unified anharmonic electron-phonon calculations in complex systems, without relying on molecular dynamics [4,5]. We demonstrate how intrinsic disorder and thermal effects modify band structures, carrier dynamics, and light-emission characteristics, providing a microscopic understanding of experimentally observed optical phenomena [2,3,5]. Extensions of this approach to emerging antiperovskite and superionic materials reveal a similarly important role of local disorder in determining their optoelectronic and transport response [6]. Our results highlight local disorder as a fundamental design parameter for the development of next-generation light-emitting materials.

For wearable and implantable health monitoring, near-infrared (NIR) light is attractive
because its low absorption in biological tissue allows deep penetration. Such
applications require flexible, efficient, and stable light sources. Colloidal
semiconductor nanocrystals (NCs) are well suited for this purpose because they
combine solution processability with efficient NIR emission. Among them,
CuInS₂/ZnS core/shell NCs are a promising RoHS-compliant alternative to
conventional heavy-metal-based quantum dots. CuInS₂/ZnS NCs emit via defectmediated
recombination involving confined hole states [1], but the role of hole
injection and transport in populating these states remains unclear.
In this work, we study the effect of the hole transport layers (HTL) on the efficiency
and stability of NIR CuInS₂/ZnS LEDs. We compare several HTL materials (TFB,
Poly-TPD, TAPC and CBP) as well as double HTL stacks with different energy levels
and hole mobilities. We find that a double HTL consisting of 10 nm CBP and 30 nm
TAPC gives the best performance in both maximum efficiency and operational
stability, achieving an EQE of 2.5%, close to the theoretical limit expected from the
10% PLQY in solution, while retaining 60% of its initial luminance after 10 h of
operation at 50 mA cm^-2. To understand the improved performance of the double
HTL, we studied how it affects charge injection, transport, and accumulation in the
device. We used hole-only devices to isolate hole transport and injection behavior.
Capacitance–voltage and capacitance–frequency measurements were performed to
probe charge accumulation and interface effects. In addition, electroluminescence
and transient electroluminescence measurements were used to analyze
recombination dynamics and device operation under bias. Correlations observed
within the datasets provide valuable insights into charge injection, transport, and
recombination dynamics, offering a deeper understanding of the mechanisms driving
device performance and stability.
This work highlights the importance of HTL engineering for CuInS₂/ZnS LEDs,
increasing the EQE from 1.3% for the best single HTL to 2.5% using an optimized
double-HTL architecture. We expect that our results can be applied also to other
RoHS-compliant quantum dots. These advances support the development of reliable
NIR light sources for future biomedical sensing applications.

The demand for high-speed X-ray imaging is rapidly increasing, which creates an urgent need for scintillators with high light yield and fast response. Halide perovskite nanocrystals (PNCs) have emerged as promising candidates due to their superior optical properties and the simplicity of their solution-based processing. However, the production of thick X-ray films—three orders of magnitude thicker than typical optoelectronic devices—causes significant material waste and a major reduction in light yield. This loss in efficiency is mainly due to strong spectral overlap, which leads to severe self-absorption. Moreover, conventional synthesis methods for PNCs often result in low reaction yields and unpredictable exciton pathways. In response, we have developed a low-temperature polar-solvent synthesis method that achieves a record reaction yield of 162 mg mL^-1 and optimized exciton routing for improved energy transfer. Notably, our method increases the Stokes shift and reduces the radioluminescence decay time to 7.19 ns, among the fastest values reported for CsPbBr₃ nanostructures. Consequently, we achieve high-speed X-ray imaging at 7,680 frames per second, along with a spatial resolution of 27.6 line-pairs per millimeter. This advancement supports the sustainable commercialization of PNC scintillators for fast, dynamic X-ray imaging.

We investigated the unusually weak electric-field effect on the trajectories of hot electrons photogenerated in Mn-doped quantum dots via Mn-mediated Auger upconversion process. This effect is equivalent to increasing the “spur radius” of the resulting solvated electrons after thermalization and solvation in liquid mediua. The short-lived (<1 ps) quasi-free electrons in the conduction band of liquid water, formed immediately after the ejection of energetic hot electrons from the QDs, undergo electric field-assisted drift, resulting in a larger travel distance before localization as solvated electrons. Because quasi-free electrons have very high mobility and experience much weaker high-frequency dielectric screening (e.g., a dielectric constant of ~2 at ~10¹³ Hz), even a modest external field with an amplitude of 1 kV/mm can alter the quasi-free-electron trajectory sufficiently to suppress geminate recombination. This process is highly beneficial for electron transfer mediated by solvated electrons by shutting off the geminate recombination channel.    

Indistinguishable single photons are a fundamental resource for photonic quantum technologies, but their generation from scalable colloidal quantum emitters remains hindered by decoherence, spectral diffusion and slow radiative dynamics. Here we demonstrate near-transform-limited single-photon emission from individual lead-halide perovskite nanorods exhibiting strongly linearly polarized single-line emission and exceptionally short radiative lifetimes. The elongated nanorod geometry simultaneously enables coherent exciton delocalization in the weak confinement regime and suppresses dielectric depolarization for the longitudinal transition, concentrating the oscillator strength into a single bright dipole. Together, these effects give rise to giant oscillator strength and single-exciton superradiance, producing exceptionally short radiative lifetimes that reduce the relative impact of dephasing processes and enable optical coherence approaching the transform limit, as confirmed by Fourier correlation spectroscopy. Two-photon quantum interference measurements based on the Hong–Ou–Mandel effect reveal highly indistinguishable photon emission from individual nanorods. Statistical analysis performed over 26 individual nanorods yields average raw and corrected visibilities of ~40% and ~50%, respectively. For nanorods on which the emission spectrum, lifetime, optical coherent time, photon statistics and Hong–Ou–Mandel interference could be simultaneously monitored throughout the measurement, corrected photon indistinguishability visibilities reach up to 80%. Ultrafast streak-camera measurements identify hot-carrier cooling occurring on a few-picosecond timescale as a residual source of temporal jitter introduced by non-resonant excitation and limiting two-photon interference. Taking this contribution into account indicates that resonantly excited nanorods could approach near-unity photon indistinguishability.

Lead halide perovskites are widely reported as promising optical gain media for optoelectronic applications in the short-pulse regime.^[1] However, their operation under continuous-wave excitation remains severely limited by thermal accumulation and gain instability. Here, we present a systematic study of amplified spontaneous emission under long-pulse and continuous-wave excitation in thermally evaporated CsPbBr₃ thin films, providing direct insight into the limits of sustained optical gain in perovskite materials. By correlating excitation pulse duration, substrate thermal conductivity, temperature-dependent emission properties, and time-resolved carrier dynamics, we establish a physical framework linking thermal dissipation to gain stability. We identify excitation-time thresholds and define optimal operating regimes, demonstrating sustained amplified spontaneous emission for pulse widths up to 30 µs in films without encapsulation or additional post-processing. Our results reveal that light-induced thermal accumulation is the dominant mechanism limiting amplified spontaneous emission under extended excitation and highlight thermal management as a critical design parameter for steady-state optical gain. These findings provide practical design rules for perovskite gain media and represent a key step toward optically pumped and, in the future, electrically pumped, continuous-wave-performing perovskite superluminescent and laser diodes.

In the first part of this talk, I will review the state of the art in first-principles modelling of key properties in these systems, including electron-phonon-limited carrier mobilities and excitonic behaviour, and examine how well hybrid functionals reproduce them.[1–3] The second part turns to materials exploration through ab initio calculations. Perovskite-inspired materials are emerging as promising candidates for both outdoor and indoor photovoltaics, due to their favourable optoelectronic properties and lower toxicity.[4] Taking the synthesized double salt AgBiI4 as a structural prototype, we investigate indium substitution as a route to lead-free compounds: replacing Bi³⁺ with In³⁺ gives the hypothetical compound AgInI₄, whose properties we assess from first principles. AgInI4 is predicted to be chemically and dynamically stable, with a direct band gap of 1.72 eV close to that of its bismuth analogue. Its photovoltaic performance, however, is markedly lower under both solar and LED illumination, as measured by the spectroscopic limited maximum efficiency metric. This limitation arises from symmetry-forbidden optical transitions and the absence of Bi-derived 6s² lone-pair states at the valence band maximum—features responsible for the strong absorption seen in AgBiI₄. A high-throughput screening of the Ag–In–I ternary phase space further reveals several stable and metastable compounds in tetrahedrally and octahedrally coordinated families, with band gaps of roughly 3.0 and 2.0 eV, respectively.[5] I will close by extending the discussion to our latest results across the Cu-In-I, Cu-Sb-I, Cu-Bi-I, and Ag-Sb-I phase spaces, providing a broader view of stability and optoelectronic trends among copper- and silver-based halides.

Organic-inorganic metal halide glasses (OIMHGs) are promising materials for high-resolution X-ray imaging due to their transparency and tunable properties. However, their practical applications are severely limited by a transition from the glassy state to a polycrystalline phase under ambient conditions, leading to significant optical and performance degradation. Herein, we systematically investigated the underlying mechanism of the rapid glass-to-crystal transition in methyltriphenylphosphonium-based hybrid materials (MTP)₂​MnBr₄ through X-ray absorption fine structure (XAFS) measurements, X-ray scattering analysis, and ab initio molecular dynamics simulations​. For the first time, we demonstrated that this transition is driven by the water molecules, which significantly influence the spatial arrangement of the organic (MTP⁺) and inorganic ([MnBr_4​]²⁻) components within the materials framework. To address the severe instability of this X-ray imaging glass in air, we developed a novel composite encapsulation strategy that integrates quartz glass layers with a waterproof parylene polymer coating. Consequently, the glass-to-crystal transition was substantially suppressed, enhancing the stability of the synthesized glass by over 100 times. This improvement enabled the material to maintain a spatial resolution of 26.3 lp mm^-1 for more than twelve months. These findings underscore the critical role of environmental stability strategies in enhancing OIMHG-based scintillators for next-generation X-ray imaging applications.

Exciton-polaritons in two-dimensional (2D) lead-halide perovskites have emerged as a promising platform for room-temperature polaritonics owing to their large exciton binding energies and high oscillator strength.[1,2] Despite rapid progress in the field, room-temperature polariton condensation in solution-processed pure-phase n=1 2D perovskites remains elusive, primarily because the microscopic mechanisms governing polariton relaxation and population build-up are still poorly understood.[3,4]

Here, we report the first demonstration of strong exciton-photon coupling in pure-phase n=1 butylammonium lead iodide (BA₂​PbI₄​) microcavities and employ femtosecond transient absorption spectroscopy to directly probe exciton-reservoir-to-polariton relaxation dynamics. By combining angle-resolved optical spectroscopy, transfer matrix method (TMM) modelling and femtosecond transient absorption measurements, we identify and asign three distinct dynamical regimes governing the nonequilibrium response of the system. An ultrafast component (<1 ps) is dominated by many-body excitonic effects, including phase-space filling, Coulomb screening, and biexciton formation, leading to transient reshaping of the cavity resonances. An intermediate timescale (5–15 ps) reveals delayed exciton-to-polariton scattering and exciton-exciton annihilation, manifested by a transient spectral response associated with the lower polariton branch. Finally, long-lived dynamics (>50 ps) are governed by dark-state and trap-mediated relaxation processes.

Our measurements reveal that efficient population accumulation at the bottom of the lower polariton branch is strongly inhibited by ultrashort polariton lifetimes, incomplete reservoir feeding, and non-radiative trapping channels. These findings provide direct ultrafast spectroscopic insight into the relaxation pathways and kinetic bottlenecks that limit polariton population build-up in solution-processed 2D perovskite microcavities, and offer important design guidelines for achieving room-temperature polariton condensation and nonlinear polaritonic phenomena in pure-phase n=1 perovskite systems

For nearly a century, alloy design has been governed by emperical rules (the Hume Rothery), which ascribe strict miscibility limits based on ionic radii and lattice strain. Halide perovskites appeared to conform rigidly to these principles, where chloride iodide alloys were found to be fundamentally unstable, limiting the accessible composition space and stable band-gap engineering.

Here, we demonstrate that these empirical miscibility rules collapse for colloidal quantum dots, where surface energy can counter destabilizing volumetric terms.

Our work flow consists of an automated high-throughput colloidal synthesis enbale us to measure the optical properties and thus map solid solution stability across 3,000 halide perovskite anion exchanged alloyed reactions. We show that nanocrystal size and thus the surface energy is crtical in reshaping perovskite miscibility boundaries. Smaller nanocrystals suppress halide segregation and the associated interfacial defect formation, producing homogeneous ternary alloys that are strictly forbidden in the bulk and are bright.

This approch portrays miscibility as a tunable design parameter and establishes nanoscale miscibility engineering as a synthetic strategy for stabilizing metastable compositions. We have integrated this high-throughput workflow into a fully operational self-driving laboratory governed by the Bayesian optimization algorithm. This autonomous platform bridges the gap between our digital predictions and physical reality, accelerating the discovery and precise synthesis of new, complex perovskite nanocrystal architectures.

The local energy landscape in semiconductors is essential for controlling charge-carrier and exciton transport in optoelectronic devices.[1] In two-dimensional metal halide perovskites (2DLPs), semiconducting metal-halide layers are separated by bulky organic spacer cations that largely suppress out-of-plane transport, making vertical heterostructures less effective for engineering charge and energy flow.[2] In contrast, lateral heterojunctions enable in-plane control of composition while preserving efficient transport within the inorganic framework, thereby providing an attractive platform for band-gap engineering. However, general synthetic strategies for the deterministic fabrication of such heterostructures remain elusive.

Here, we introduce a versatile one-pot sequential recrystallization strategy for fabricating lateral 2DLP heterostructures.[3] The method exploits differences in solubility and crystallization kinetics, while the sequence, timing, and composition of precursor injections determine the resulting heterostructure architecture. This approach enables the formation of heterojunctions between materials with different halides and metal cations and can be extended to multiple heterojunctions incorporating up to three different halides. Furthermore, we identify two distinct heterostructure morphologies, core-frame and triptych-shaped, that arise from different crystallographic orientations of the core crystal, leading to facet-selective growth of the surrounding phase. The resulting heterostructures exhibit crystalline junctions, tunable multicolour emission, and optical and electronic coupling across the interfaces. Beyond demonstrating a broad range of heterostructure architectures in 2DLPs, this sequential recrystallization strategy has the potential to provide a general route for band-gap engineering in solution-processable low-dimensional semiconductors.

Advances in the colloidal synthesis and surface chemistry of tin-halide perovskite nanomaterials resulted in improvements of their chemical stability and luminescence efficiency. The photophysics of these nanomaterials remains though incompletely understood, with various studies reporting multiple near band-edge emission channels at cryogenic temperatures, attributed to free, bound and self-trapped excitons, defects, and different crystal configurations or nanostructure dimensionalities.^1-5

Herein, we report on the variable-temperature photoluminescence (PL) of nanostructures of CsSnI₃ and FASnI₃ films^6,7. Both types of films exhibit regions with dual near band-edge emission at cryogenic temperatures however the spectral and temporal characteristics of the doublet emission differ significantly between the inorganic and hybrid perovskite structures. In CsSnI₃, the two bands exhibit small energetic separation of 25–30 meV, with the low-energy (LE) peak progressively quenching and thermally repopulating the higher-energy (HE) transition, which remains the dominant emissive species at elevated temperatures. Furthermore, the LE emission exhibits a superlinear excitation PL dependence compared to the purely linear behaviour of the HE band. Based on such observations, HE and LE bands were tentatively assigned to free (HE) and surface or defect-bound (LE) excitons, respectively¹.

In contrast, the dual near-band-edge emission in FASnI₃ exhibits a substantially larger energy separation of 90–100 meV, while increasing temperature can lead to the dominance of either the LE or the HE band. Furthermore the integrated area of both  features exhibit linear dependence with fluence and distinct excitation PL (PLE) bands. The data raise the possibility that the dual emission in FASnI₃ may originate on exciton recombination in alternative local crystal configurations or band-edge minima. The results provide preliminary insight into the microscopic origin of low-temperature luminescence and highlight potential differences in exciton localization and structural characteristics of Cs- and FA-based tin-halide perovskite nanostructures.

InAs QDs are highly promising materials for advanced IR optoelectronics. However, their performance is often hindered by the presence of dense trap states at the valence band (VB). A common remediation strategy involves post-treating the InAs surface with Zn. While Zn effectively passivates the surface, a critical synthetic limitation persists: Zn cannot be directly alloyed into the internal InAs core, restricting further structural and electronic tuning.

To overcome this bottleneck, we propose an inverted alloying strategy: rather than forcing Zn into InAs, we introduce In into a surrounding Zn-based matrix. Selecting ZnTe as the ideal host due to its highly favorable lattice match with InAs, we investigate the electronic properties of an InAs@Zn_1-xIn_xTe core-shell architecture. Our models demonstrate that In readily alloys into the ZnTe shell, systematically altering its electronic structure. Critically, by modulating the In concentration within the ZnTe shell, we can actively tune the band alignment from an initial reverse type-II – where holes are delocalized across the structure while electrons remain core-confined – to a type-I system.

Despite this successful band engineering, implementing this strategy via standard chloride-based precursors introduces a secondary challenge: the accumulation of Cl molecular orbitals near the VB, which would severely degrade the PLQY. Instead, we demonstrate that utilizing F-based precursors (e.g., InF₃) effectively pushes these halide trap states much deeper in energy, yielding a trap-free valence band. Ultimately, the synergistic combination of In shell-alloying and surface fluorination can potentially provide a robust type-I architecture with clean bandgaps, offering a direct pathway to highly efficient InAs IR emitters.

Metal-halide perovskites (MHP) emerged as highly interesting materials for photovoltaics and light emission with highly competitive efficiencies.[1] Low-dimensional MHP, where semiconductor octahedra are sandwiched in between organic molecules, feature several highly attractive properties: (i) strong quantum and dielectric confinement, and therefore strongly bound excitons; (ii) a huge parameter space to design their composition, providing an extensive toolbox to tailor their structural, mechanical, and optoelectronic properties.[2] While 2D-MHP thin films have been successfully implemented in LEDs and solar cells, developing high quality single crystals for photonics is another very promising direction. Single crystals allow for a distinct correlation of their optical properties to their structural properties, thereby providing deep insight into their exciton level structure, electron-phonon coupling, and relaxation dynamics. [3-6]

We have developed a microcrystal growth process based on dissolution and recrystallization that allows to fabricate 2D-MHP microcrystals with rectangular shape and highly homogeneous thickness in the few 100 or sub-100 nm range (Fig.1). [7] We demonstrate microcrystal fabrication with different halides, metal cations and organic cations comprising aliphatic chains and aromatic phenyl rings, and on a variety of substrates. The tunable band gap and high refractive index renders such microcrystals extremely promising for photonics and polaritonics.

Recently, we extended the microcrystal fabrication to heterostructures, [7, 8] either by solution-based anion exchange, or by sequential growth of different phases (for example with different halides) in a single microcrystal, in core-shell or core frame geometries. With this approach we also managed to fabricate triple halide microcrystals, for example with decreasing band gap from the core to the outer regions. Optical emission coupling to the lower band gap regions reduces reabsorption, which is advantageous for next-generation light-management and radiation-detection materials.

References:

H. Dong, et al., eLight, 3,3,(2023).

L. Mao, et al., J. Am. Chem. Soc., 141, 1171 (2019).

R. Krahne, et al., Nano Lett., 24, 11124 (2024).

R. Krahne, et al., Acc. Chem. Res., 57, 2476 (2024).

S. Kutkan, et al., Nanoscale, 15,12880 (2023).

B. Dhanabalan, et al., Adv. Mater., 33, 2008004 (2021).

A. Schleusener, et al., Adv. Mater., 36, 2402924 (2024).

A. Griesi, et al., Nanotechn., 35, 105204 (2024).