Halide perovskites and their structural analogs, perovskitoids, are increasingly recognized for their outstanding photoluminescence properties in addition to their semiconductor performance. While three-dimensional (3D) and two-dimensional (2D) halide perovskites have been extensively studied for photovoltaic applications, their potential in light-emitting devices is equally compelling, driven by their long carrier lifetimes, efficient radiative recombination, and compositional tunability. Perovskitoids, with their diverse structural motifs, enable further control over dimensionality, exciton confinement, and emission bandwidth. By rationally selecting organic spacer cations, we can fine-tune crystal packing and stabilize architectures that favor enhanced photoluminescence and suppressed nonradiative pathways. Notably, heterostructures composed of perovskitoid-perovskite layers exhibit reduced ion migration and improved exciton confinement, leading to more stable and efficient emissive behavior. A prime example is the 2D perovskitoid (organic cation)₈Pb₇I₂₂, which demonstrates high-quality film formation and effective surface passivation, crucial for light-emitting device fabrication. In parallel, the rhenium chalcohalide Rb₆Re₆S₈I₈ exemplifies a new class of photoluminescent cluster-based materials. It exhibits broad emission from 1.01 to 2.12 eV with a quantum yield of 42.7% and a long PL lifetime of 77 μs at room temperature. The solubility of Rb₆Re₆S₈I₈ in polar solvents allows for solution processing into thin films, enabling the fabrication of prototype LEDs and highlighting its promise for future optoelectronic applications.

InP-based quantum dots (QDs) represent the major commercial success of colloidal semiconductor nanocrystals (NCs). A combination of the robust, mostly covalent, structure and nontoxic nature of the constituent elements makes them a QD material of choice for display and LED technologies.^1,2 Despite successful commercial realization, InP NCs still lack synthetic versatility and robustness, seen, for instance, as a continued quest to substitute a commonly used pyrophoric and expensive tris(trimethylsilyl)phosphine precursor.^3-5 Herein, we propose solid-state, nonpyrophoric, and synthetically readily accessible acylphosphines as convenient phosphorus precursors for the synthesis of InP NCs. When combined with suitable anionic nucleophiles, such as arylthiolates, both tris(acyl)phosphines and indium complexes of bis(acyl)phosphines act as efficient sources of the P^3– anion, as corroborated by NMR spectroscopy and powder X-ray diffraction studies. This type of reactivity is utilized in colloidal synthesis of uniform InP QDs with well-defined excitonic features in their optical absorption spectra, spanning 460–600 nm. The conversion kinetics and therefore the final NC size are controlled by the nature of acyl substituents and by the use of either indium or zinc long-chain carboxylates as ligands. The proposed acylpnictide route is anticipated to foster the development of other metal phosphide and metal arsenide NCs.

Dilute magnetic doping of wide bandgap semiconductors has attracted significant interest due to its potential for tailored optical and spin-photonic properties. Over the past decades, the solution processability and high defect tolerance of halide perovskites have driven explosive advancements in the field. In contrast, vapor-phase growth techniques offer enhanced control over chemical composition, crystallography, and morphology, owing to their highly kinetic, non-equilibrium nature. Metal halide perovskites synthesized via vapor methods often exhibit unique properties unattainable through solution-based approaches.

In this presentation, I will discuss the remarkable crystal distortion observed in Mn2+-doped BA2PbBr4 single crystals grown by chemical vapor deposition. These micron-scale single crystals exhibit well-defined monocrystalline habits with no apparent grain boundaries, providing an ideal platform to investigate the effects of Mn2+ incorporation on crystal structure and optical properties. Structural analysis reveals substantial distortion, including a continuous morphological transition from square nanoplatelets to parallelograms, characterized by an in-plane shear of up to ~6° and an out-of-plane contraction of 9.7% at the highest Mn2+ concentrations. This degree of deformation surpasses typical values observed in doped semiconductors by an order of magnitude. Density functional theory calculations indicate that the dopant-induced structural distortion is driven by a thermodynamic energy gain. Static and time-resolved photoluminescence spectroscopy confirms successful Mn2+ incorporation, evidenced by characteristic emission at 600 nm and an approximate radiative lifetime of 0.3 ms. Uniform dopant incorporation is further supported by the hyperfine structure observed in the electron paramagnetic resonance spectrum and a paramagnetic response detected via superconducting quantum interference device measurements. These findings provide key insights into dopant-induced structural modifications and establish a foundation for the rational design of dilute magnetic semiconductors for spin-based information technologies.

Colloidal quantum dots (QDs) are widely used as a printable semiconductor with opto-electronic properties tunable by size. Applications in display, projection or lighting rely on QDs emitting visible light, whereas QDs sensitive for infrared light are used in imaging systems. Here, we will discuss ongoing work at Ghent University on InP-based QDs, a key material for QD technology at visible wavelengths.

After outlining the requirements for luminescent color conversion, the different aspects that enable InP/ZnSe/ZnS QDs to be formed with a photoluminescence quantum yield of 95-100% will be discussed as a first step. Particular attention will be paid to the QD geometry, including the composition of the core/shell interface and the shell outer surface. Next, we will discuss the opto-electronic properties of InP/ZnSe QDs, with a specific focus on the core/shell band alignment and the occurrence of stimulated emission under high-power optical pumping. Finally, we will address the prospects of InP/ZnSe QDs for on-chip color conversion, where we will move from successful proof-of-concept demonstrators to an analysis of stability-limiting factors.

To conclude the presentation, we will give a future outlook on science and technology based on III-V QDs.

All-inorganic halide perovskites, such as CsPbBr₃, are leading candidates for next-generation photonic and display technologies due to their high color purity and quantum efficiency [1]. However, their practical implementation is limited by poor moisture stability due to their inherently ionic nature. Embedding CsPbBr₃ within a Cs₄PbBr₆ host is a widely used strategy for improving stability due to their structural compatibility [2]. However, the resulting composites often suffer from low emission intensity as large non-emissive Cs₄PbBr₆ domains (>100 nm) dominate over the smaller luminescent CsPbBr₃ nanocrystals (<5 nm). Additionally, they exhibit poor solution dispersibility, and rapid degradation upon water exposure.

In this study, we introduce a novel Phosphate Matrix Assisted Re-Precipitation (PARP) strategy by incorporating exfoliated zirconium phosphate (Exf-ZrP) nanosheets as an inorganic matrix to guide perovskite crystallization. Utilizing a modified ligand-assisted reprecipitation method, we integrated less than 1 wt% Exf-ZrP during the nucleation of perovskite. Despite this minimal loading, this matrix-assisted route significantly enhances the perovskite dispersion and promotes defect passivation. Further, this PARP process enhances the growth of CsPbBr₃ domains (up to 45 nm) and suppresses the formation of large, non-emissive Cs₄PbBr₆ domain. As a result, the photoluminescence quantum yield (PLQY) is boosted to 75%, representing a 2.4× improvement over unassisted synthesis.

Importantly, we demonstrate for the first time that the phosphate matrix enables a solid-state, water-assisted phase transformation of Cs₄PbBr₆ into CsPbBr₃ without structural collapse. Unlike conventional liquid–liquid methods [3] that require biphasic systems (e.g., water–toluene mixtures) and large solvent volumes, our approach achieves the transformation simply by exposing the solid composite to water, eliminating the need for toxic organic solvents. This controlled, matrix-guided conversion enhances fluorescence by 1.2× and redshifts the emission to 530 nm, moving closer to the pure green required for display technologies.

Our results underscore the multifunctional role of the inorganic phosphate matrix: (i) it promotes the growth of high-quality CsPbBr₃ crystals, enhancing optical performance; (ii) it stabilizes the composite by passivating surface defects; and (iii) it mediates a controlled, water-triggered solid-state phase transformation. The proposed strategy offers a versatile framework for integrating metal phosphate matrices with halide perovskite systems, and solvent-free pathway to engineer light emitting perovskites for high-performance.

For nearly two decades, CdSe nanoplatelets (NPLs) have captured the spotlight as promising materials for optoelectronic applications, from LEDs to displays, thanks to their exceptional optical properties. Yet, lacks in understanding their formation often lead to low yields, unwanted side products, and unclear surface chemistry – limiting their use in devices. We demonstrate that the preparation method of the cadmium carboxylate precursors plays a critical role in the quality and optical properties of the formed NPLs. We focused our study on cadmium oleate and myristate, the most commonly used precursors in CdSe NPLs synthesis. Using a combination of thermal analysis (TGA), FT-IR and SAXS, we reveal clear differences in the structure and crystallinity of these precursors. In situ SAXS studies show that these structural variations affect the precursor’s dissolution kinetics during synthesis, ultimately affecting NPLs thickness and uniformity. These findings are supported by UV-Vis spectroscopy and TEM, highlighting the strong link between precursor structure and NPLs properties.

Precise synthetic control over the doping polarity of colloidal nanocrystals offers a versatile platform to engineer their optoelectronic properties for efficient infrared (IR) photon harvesting. In this work, we present a synthesis-driven approach that enables switchable polarity by leveraging redox-active pnictogen precursors and carefully tuning surface reaction pathways. By controlling precursor oxidation states, ligand chemistry, and reaction kinetics, we achieve selective formation of stable n-type and p-type nanocrystals with tunable carrier densities and band alignments. This intrinsic polarity control is accomplished during synthesis without the need for additional post-treatments, providing a scalable and reproducible strategy for material fabrication. Building on this polarity modulation, we design advanced device architectures, including homojunction and barrier-type structures, that are specifically optimized to enhance charge separation, minimize recombination losses, and suppress dark current in IR photodetectors. The integration of synthetic polarity control with rational device structure engineering provides new opportunities to develop high-performance, solution-processed IR optoelectronic devices and contributes valuable design principles for next-generation nanocrystal-based technologies.

The assembly of nanoparticle building blocks is a compelling platform for designer, complex  materials. Monodisperse nanocrystals (NCs) functionalized with capping ligands readily form long-range ordered superlattices (SLs) [1], in which novel collective properties can be adjusted by varying composition, shape, and size of the NCs. Lead halide perovskite NC SLs have been much thought after in this research area due to collective phenomena such as superfluorescence, which was first observed in 3D single-component CsPbBr₃ NC SLs [2]. Co-assembly of CsPbBr₃ NCs with a variety of other building blocks has enabled the exploration of structure-properties relationships of superfluorescence and the design of diverse novel SLs.[3]

This study focuses on assembling CsPbBr₃ nanocubes and Au nanospheres into binary SLs, which have the potential to exhibit novel collective properties arising from exciton-plasmon interactions. Six different types of SLs were obtained, namely NaZn₁₃, MgZn₂, CaCu₅, AlB₂, AB₂ and NaCl, and similar superstructures were extended using building blocks of different sizes (from 5 to 46 nm). We demonstrate how the superlattice structure and NCs size affect the collective optical properties.

Colloidal semiconductor Quantum Dots (QDs), often considered as artificial atoms, have reached an exquisite level of control, alongside gaining fundamental understanding of their size, composition and surface-controlled properties, as recognized by the Nobel prize in Chemistry 2023. Their tuned characteristics and scalable bottom-up synthesis accompanied by the applicability of solution based manipulation, have led to their wide implementation in displays, lasers, light emitting diodes, single photon sources, photodetectors and more.

For the next step towards enhancing functionalities of quantum dots, inspired by molecular chemistry, we introduce the controlled linking and fusion of two core/shell quantum dots creating an artificial molecule manifesting two coupled emitting centers.¹ Accordingly, the coupled colloidal quantum dot molecules (CQDMs) present novel behaviors differing than their quantum dot building blocks. Utilizing single particle spectroscopy, especially a version of heralded spectroscopy, we distinguish between localized versus segregated multiexciton states. ^{2, 3}  Furthermore, this also affects the multiexciton dynamics in CQDMs compared with the monomer QDs. Moreover, such CQDMs open the path to a novel electric field induced instantaneous color switching effect, allowing color tuning without intensity loss, that is not possible in single quantum dots.⁴ All in all, such quantum dot molecules, manifesting two coupled emission centers, may be tailored to emit distinct colors, opening the path for sensitive field sensing and color switchable devices such as a novel pixel design for displays or an electric field color tunable single photon source.

Colloidal quantum dots (QDs) with infrared (IR) absorption and emission are promising candidates for next-generation optoelectronic applications, such as solar concentrators, light-emitting diodes, optical communication systems, biological imaging, and night or fog vision devices.¹ To date, the best-performing IR QDs have been based on Pb- and Hg-chalcogenides, whose synthesis protocols are now well established.² However, the inherent toxicity and environmental concerns associated with these materials limit their suitability for consumer and biomedical technologies, prompting a shift toward less toxic alternatives.³ Indium arsenide (InAs) QDs present a viable alternative due to their RoHS compliance and size-tunable bandgap, which spans a broad spectral range from 700 to more than 1700 nm.⁴ Despite their potential, early InAs QD syntheses relied on the use of pyrophoric, expensive, and commercially limited arsenic precursors. This challenge was mitigated with the introduction of tris(dimethylamino)arsine (amino-As), a non-pyrophoric, cost-effective As precursor.⁵ The key characteristic of amino-As is that it requires the use of a reducing agent to convert As³⁺ to As^3-, which is necessary for the formation of InAs.

Despite the advances made with amino-As synthesis routes, achieving InAs QDs with high photoluminescence (PL) quantum yield (QY) beyond 1000 nm remains challenging.⁶ Moreover, syntheses using amino-As typically rely on reducing agents that are either low-boiling or dissolved in volatile solvents, leading to reaction instability, including temperature fluctuations, and hazardous boiling bursts.

To address these limitations, we synthesized a novel high-boiling reducing agent, which enabled the development of stable and scalable reaction pathways for amino-As-based InAs QDs. In detail, we could produce InAs QDs with excitonic absorption peaks tunable down to 935nm, which, after ZnSe shelling, exhibited impressive PLQys of 75% (at 905 nm) and 60% (at 1000 nm). Larger InAs QDs, with excitonic absorption and emission extending into the short-wave infrared (SWIR) region, were also synthesized by developing a seeded growth approach to increase the QD size. Remarkably, the thermal stability of our reducing agent enables continuous precursor injection without triggering boiling-related issues. Upon ZnSe shelling QDs with record PLQYs of 46% at 1160 nm, 38% at 1250 nm, 32% at 1335 nm, and 23% at 1430 nm were achieved. 

These advancements collectively establish a robust, scalable, cost-effective, and safer synthetic route for producing highly luminescent InAs QDs with tunable emission spanning the near-IR to SWIR. This work significantly advances the practical viability of InAs-based nanocrystals for integration into next-generation IR optoelectronic applications, including biomedical diagnostics, environmental sensing, and telecommunications.

Tin-based metal halide perovskites are emerging as a compelling class of materials in the pursuit of efficient and eco-friendly photovoltaics. Although lead triiodide perovskites have recently achieved exceptional performance in optoelectronic applications, concerns about their wide bandgap (1.5–1.6 eV), lead toxicity, and environmental impact continue to fuel the search for safer alternatives.

Tin perovskites have gained attention as a less hazardous option, but their development has been hindered by chemical instability and defect formation. Conventional approaches relying on solvent and additive engineering often suffer from chemical instability—primarily due to electron donating solvents that accelerate the oxidation of Sn²⁺ to Sn⁴⁺ [1], leaving behind detrimental by-products and high background hole concentration. [2] To overcome these limitations, solvent-free deposition strategies, which have demonstrated to be advantageous in lead-based systems, are being explored for tin perovskites. Techniques such as thermal evaporation offer precise control over stoichiometry, uniformity over large areas, and compatibility with scalable manufacturing—all under inert, vacuum conditions ideal for handling oxidation-sensitive tin compounds.

Despite these advantages, the fabrication of high-quality tin halide perovskite films via vacuum methods remains in its infancy, with only a few successful demonstrations and limited understanding of the resulting materials’ intrinsic properties. [3] [4] [5]

In this study, we first report the fabrication of additive-free formamidinium tin triiodide (FASnI₃) thin films via co-evaporation under vacuum. The resulting films display a substantial suppression of Sn⁴⁺ species, indicating reduced oxidation and intrinsic semiconducting characteristics with supressed tendency toward self-doping effects. The measured optical bandgap (~1.31 eV) closely aligns with theoretical predictions, affirming the structural integrity of the material. These findings position co-evaporation as a viable and scalable pathway for advancing lead-free perovskite technologies in next-generation optoelectronic applications.

Lead-halide perovskite nanocrystals (LHP NCs) have attracted substantial interest due to their potential in a wide range of optoelectronic and photonic applications. These materials provide notable advantages, including solution-processable, low-temperature, and tunable synthesis methods, high photoluminescence quantum yields (PLQY) owing to their inherent defect tolerance, fast luminescence lifetimes, and ease of integration into devices. However, a major challenge in device integration is their generally small Stokes shift, just a few tens of meV, which causes significant spectral overlap between excitonic absorption and emission [1]. This overlap leads to significant self-absorption, especially problematic for applications involving light transmission through devices, such as luminescent solar concentrators, waveguides, photonic fibers, and radiation-detection scintillators [2]. Increasing the Stokes shift of LHP NCs without compromising their sharp, fast excitonic emission remains difficult because high halide mobility dissolves the compositional gradients needed for core/shell architectures, which are among the most effective strategies for creating Stokes-shifted emission. In this account, an important phase can be CsPb(Cl_xI_1-x)₃, provided the emission originates from the CsPbI₃ phase and the absorption from the CsPbCl₃ phase, resulting in a large Stokes shift. Unfortunately, efforts to stabilize this phase have not been successful till now, leading to complete substitution of Cl- ions with I- ions [3]. In this presentation, I will describe a key strategy involving a surface passivation step before halide exchange that offers a straightforward solution: treating CsPbCl₃ NCs with CdCl₂ eliminates halide-vacancy traps, enhances emission yield, and critically prevents inward diffusion of I⁻ during a subsequent Cl^- to I^- exchange. As a result, the reaction is halted after a few monolayers, producing CsPbCl₃/CsPbI₃ core/shell NCs that absorb at 3.14 eV and emit at 1.91 eV, with an apparent Stokes shift exceeding 1 eV. This reduces reabsorption losses, as confirmed through waveguiding experiments. Density functional theory calculations confirm the formation of an inverted type-I heterojunction, while transient absorption and fluence-dependent PL measurements reveal sub-60 ps energy transfer from the core to the shell. The entire process is solution-processed and adjustable via PbI₂ dosage, providing a practical pathway for reabsorption-free LHP emitters in photon management applications.

Colloidal quantum dots (QDs) exhibit complex electronic, optical, and structural properties, making them essential in optoelectronics, photovoltaics, and nanomedicine. Despite advances in understanding QD surface chemistry and trap state formation, key questions remain, particularly regarding surface effects on electronic properties. Addressing these challenges requires accurate theoretical modeling.
In our group, extensive density functional theory (DFT) studies have explored QDs up to ∼4.5 nm, revealing that increasing system size leads to band gap collapse and facet-specific localization of frontier orbitals. We also found that introducing surface vacancies induces reconstructions that widen the band gap and delocalize charge carriers, emphasizing the critical role of surface geometry in defining QD properties. However, DFT-based approaches are computationally expensive, limiting their application to larger, more realistic systems and longer timescales.
To overcome these limitations, we are preparing to employ machine learning force fields (MLFFs) trained on DFT datasets. A key aspect of this approach is the inclusion of long-range electrostatic interactions during the training process to ensure the structural stability of QDs, which is crucial for accurately capturing their surface and bulk properties. These MLFFs aim to provide DFT-level accuracy at significantly reduced computational costs, enabling the study of larger QD systems and their dynamic behavior over extended timescales.
We anticipate applying ML-based models to various QD compositions, including CdSe, InP, PbSe, and CsPbBr₃, facilitating more efficient investigations into QD growth and optoelectronic integration. This transition highlights the transformative potential of machine learning in advancing the computational toolkit for nanomaterial design.

Indium antimonide (InSb) quantum dots (QDs) are of growing interest for infrared optoelectronic applications due to their narrow bandgap, strong quantum confinement, and tunable absorption in the short-wave to mid-wave infrared (SWIR–MWIR) range. Realizing high-quality, monodisperse InSb QDs with controlled surface chemistry remains challenging, particularly for solution-processed technologies.

We will discuss the critical synthetic parameters influencing the evolution of these intermediary species into well-defined QDs, including precursor chemistry, stoichiometry, and temperature-dependent processing steps. Particular attention will be given to the mechanistic aspects of nanoparticle formation and growth, and how these relate to size distribution and optical behavior.

We demonstrate the formation of intermediary nanoparticles (2–4 nm) at room temperature, which serve as precursors to high-quality InSb QDs. Through a comparison of hot-injection and heating-up methods, we identify the heating-up approach as more effective in producing materials with well-defined excitonic features. Using this method, we achieve precise size control and extend the absorption up to 2200 nm while maintaining high optical quality.

In addition, we will address the role of surface chemistry in ensuring colloidal stability and enabling integration into solution-processed device architectures. Strategies for ligand exchange and ink formulation will be presented, with a focus on their impact on electronic properties and film quality. Together, these insights contribute to a more controlled and reproducible approach for the synthesis and processing of infrared-active InSb QDs.

ABX₃-type lead halide perovskites have emerged as outstanding semiconductor materials for photovoltaic and light-emitting applications, owing to their remarkable optical and electronic properties and facile fabrication via low-temperature chemical solution processes. Their ionic and soft crystal structures give rise to pronounced electron-phonon and phonon-phonon interactions, which critically influence their optoelectronic and thermal properties [1,2]. Strong electron-phonon coupling in halide perovskites has been linked to a variety of unique phenomena, including enhanced carrier masses [3], efficient anti-Stokes luminescence [4], phonon bottleneck effects in hot carriers [5], phonon-assisted luminescence [6], and laser cooling [7,8]. Electron-phonon interactions in semiconductors are discussed in terms of short-range and long-range interactions [1]. In conventional inorganic semiconductors, a strong correlation exists between these two types of coupling constants [1]. However, halide perovskites exhibit an unusual suppression of short-range interactions, preventing the formation of strongly localized polarons [9]. This distinctive behavior positions halide perovskites as unique materials from the perspective of electron-phonon interactions. This talk discusses the electron-phonon interactions in halide perovskites, summarizing our group’s research on the photophysical properties of hybrid halide perovskites.

While single-photon emission continues to drive a broad range of photonic quantum technology, an important next goal in quantum-light generation is the preparation of correlated N-photon bundles, e.g., photon pairs. These higher-order quantum-light resources may act as enabling ingredients for various quantum technologies, including quantum teleportation¹ and quantum metrology.² A prototypical approach to generating entangled photon pairs has been the exploitation of the radiative biexciton cascade (├ |XX⟩ to ├ |X⟩ to ├ |0⟩) in individual epitaxially grown semiconductor quantum dots (QDs)^{3, 4}. In an effort to search for scalable and solution-processable alternative photon-pair sources, we here investigate and engineer the radiative biexciton cascade in individual colloidal CsPbBr₃ QDs. By matching their size-dependent biexciton binding energies^5-9 to their size-independent phonon energies,^{8, 10, 11} we demonstrate the generation of temporally correlated and energy-degenerate photon pairs in large (> 15 nm) CsPbBr₃ QDs. Under pulsed excitation and at cryogenic temperature, we observe a pronounced photon bunching, with g⁽²⁾(0) up to 7 in Hanbury Brown and Twiss measurements. The excitation-dependent bunching is quantitatively reproduced by multi-color numerical calculations,¹² revealing the cooperative biexciton and phonon-mediated exciton emission as the origin of the pronounced bunching. Our findings provide new insights into the energy-degenerate photon-pair generation in this scalable and highly engineerable quantum-light emitting platform, marking an important step towards their application in quantum-information technologies.

REFERENCES

(1) Bouwmeester, D.; Pan, J.-W.; Mattle, K.; Eibl, M.; Weinfurter, H.; Zeilinger, A. Nature 1997, 390 (6660), 575-579.

(2) Giovannetti, V.; Lloyd, S.; Maccone, L. Physical review letters 2006, 96 (1), 010401.

(3) Huber, D.; Reindl, M.; Huo, Y.; Huang, H.; Wildmann, J. S.; Schmidt, O. G.; Rastelli, A.; Trotta, R. Nature communications 2017, 8 (1), 15506.

(4) Heindel, T.; Thoma, A.; von Helversen, M.; Schmidt, M.; Schlehahn, A.; Gschrey, M.; Schnauber, P.; Schulze, J.-H.; Strittmatter, A.; Beyer, J. Nature communications 2017, 8 (1), 14870.

(5) Zhu, C.; Nguyen, T.; Boehme, S. C.; Moskalenko, A.; Dirin, D. N.; Bodnarchuk, M. I.; Katan, C.; Even, J.; Rainò, G.; Kovalenko, M. V. Advanced Materials 2022, 2208354.

(6) Tamarat, P.; Prin, E.; Berezovska, Y.; Moskalenko, A.; Nguyen, T. P. T.; Xia, C.; Hou, L.; Trebbia, J.-B.; Zacharias, M.; Pedesseau, L. U. Nature Communications 2023, 14 (1), 229.

(7) Nguyen, T.; Blundell, S.; Guet, C. Physical Review B 2020, 101 (12), 125424.

(8) Amara, M.-R.; Said, Z.; Huo, C.; Pierret, A.; Voisin, C.; Gao, W.; Xiong, Q.; Diederichs, C. Nano Letters 2023, 23 (8), 3607-3613.

(9) Cho, K.; Sato, T.; Yamada, T.; Sato, R.; Saruyama, M.; Teranishi, T.; Suzuura, H.; Kanemitsu, Y. ACS nano 2024, 18 (7), 5723-5729.

(10) Zhu, C.; Feld, L. G.; Svyrydenko, M.; Cherniukh, I.; Dirin, D. N.; Bodnarchuk, M. I.; Wood, V.; Yazdani, N.; Boehme, S. C.; Kovalenko, M. V. Adv. Opt. Mater. 2024, 2301534.

(11) Cho, K.; Tahara, H.; Yamada, T.; Suzuura, H.; Tadano, T.; Sato, R.; Saruyama, M.; Hirori, H.; Teranishi, T.; Kanemitsu, Y. Nano Lett. 2022.

(12) Nair, G.; Zhao, J.; Bawendi, M. G. Nano letters 2011, 11 (3), 1136-1140.

We investigate single CsPbBr₃ quantum dots (QDs) as quantum light sources operating at cryogenic temperatures. The 25 nm large QDs are placed into a tunable, open Fabry-Pérot microcavity with a wavelength-scale Gaussian deformation to enhance their radiative decay rate and brightness via the Purcell effect. The acceleration of the emission is quantified by the Purcell factor, F_P, which is proportional to the ratio between the quality factor, Q, and the effective modal volume, V, of the cavity, and is maximized when the QD is spectrally and spatially in resonance with a cavity mode. This cylindrically symmetric cavity configuration supports Laguerre-Gaussian (LG) modes that are associated with non-zero orbital angular momentum (OAM), which is of interest for quantum communication and sensing applications. Coupling the QD emission to these modes enables the direct generation of single photons in well-defined LG states selected by tuning of the cavity length.

We realize Purcell-enhanced emission with F_P = 4.2 at 6 K, where however the measured cavity-accelerated decay is limited by the instrumental time resolution. At 50 K, where the radiative decay time of perovskite QDs is longer, we find up to F_P = 18.1, closer to the theoretical maximum of F_P = 38 for our cavity. The lifetime reduction is accompanied by enhanced brightness and purity due to funnelling of the emitted photons into one specific mode and suppression of parasitic emission like biexcitons, as evidenced by improved photon anti-bunching.

Furthermore, by in-situ tuning of the cavity, we can bring different LG modes into resonance with the QD emission. We show that the emitted single-photon streams have LG spatial profiles of different radial and azimuthal orders, selected by tuning of the cavity resonance.

Our work demonstrates effective generation of single photons from colloidal perovskite QDs in controllable LG modes, which are promising for quantum photonic applications that use OAM states.

The term ‘molecular polaritonics’ is used to describe the strong coupling of molecular materials to confined optical fields, and the formation of new hybrid states, termed polaritons, that are a linear superposition between excitons and photons. In the past few years, polaritons have become a readily accessible platform to study fundamental and intriguing phenomenology at room-temperature, with a few realisations among many include Bose-Einstein condensation, access to topological physics and ultralong-range energy transfer. Additionally, it has been recently shown that the excited-state reactivity of molecular materials could be altered in polaritonic systems [1]. One of the most fundamental photophysical reactions in molecular materials is photobleaching; an irreversible event that cause permanent photo-degradation of the organic molecules.  This is particularly important in organic optoelectronic devices because it can cause permanent damage on the devices and limit their operational performance and stability. In recent studies, it was shown that the photobleaching could be suppressed in dye-coated plasmonic nano-structures [2] as well as microcavities filled with P3HT molecules [3] when compared with control films.

Here, we introduce a new microcavity design that allowed the observation and quantification of the photobleaching effect. A shown in Figure 1, we have used the Transfer Matrix Method (TMM) to design and fabricate a series of multilayered optical microcavities containing as an active material the J-aggregated dye TDBC that has been sandwiched between two SiO₂ spacer layers. Following careful design of the thicknesses of the microcavities’ various layers, we have been able to realize structures that operate in either the weak or strong coupling regime while maintaining similar design characteristics. Most importantly, the thickness of the active molecular layer used was between 20 and 30 nm allowing the entire number of molecules to either reside at the node or anti-node of the confined electric field, rather than being distributed along the total volume of the microcavity. Using this approach, we could maximise or fully suppress the cavity effects depending on the selected design.

Optical microcavities have been studied using a k-space imaging technique measuring white-light reflectivity and photoluminescence, with the data being fitted with a standard coupled oscillator model to allow light-matter interaction parameters to be extracted. Next, we have studied the photostability of weakly and strongly coupled microcavities as well as non-cavity control films, through photoluminescence measurements. Following extended laser exposure of the samples, we observed a suppression of the photobleaching rate in strongly coupled microcavities as compared to weakly coupled structures and non-cavity control films.

II-VI and III-V core-only colloidal quantum dots (QDs) often suffer from surface defects that create deep trap states, severely limiting photoluminescence efficiency and device performance. These traps typically originate from undercoordinated anions at anion-rich facets, promoting non-radiative recombination. While surface passivation strategies can help, achieving complete and stable passivation remains challenging and highly material-dependent. Core@shell architectures provide an alternative by isolating the optically active core, but can introduce new complications at the core-shell interface. In particular, core@shell systems combining materials from different families, such as III-V@II-VI heterostructures commonly used to shell III-V QDs, face charge imbalances due to bonding differences and lattice mismatch, which can in turn create interfacial traps.
To address these challenges, we present a computational framework based on density functional theory and Bader charge analysis to investigate how covalency and ionicity together influence the energetic positions of molecular orbitals (MOs) at the valence and conduction band edges. Using InAs as a reference core QD model, we compare combinations of zinc-blende materials used as shells from both III-V and II-VI families. We examine the impact of different facets on the electronic structure, focusing on the emergence of facet-specific, localized trap states at these interfaces. Our analysis breaks down the contributions of covalency and ionicity to MO stability, providing guidance for the design of more robust and efficient QD heterostructures.

Colloidal perovskite quantum dots (PQDs) are an exciting platform for on-demand quantum, and classical optoelectronic and photonic devices. However, their potential success is limited by the extreme sensitivity and low stability arising from their weak intrinsic lattice bond energy and complex surface chemistry. Here we report a novel platform of buried perovskite quantum dots (b-PQDs) in a three-dimensional perovskite thin-film, which overcomes surface related instabilities in colloidal perovskite dots. The b-PQDs demonstrate ultrabright and stable single-dot emission, with resolution-limited linewidths below 130 μeV, photon-antibunching (g²(0)=0.1), no blinking, suppressed spectral diffusion, and high photon count rates of 10⁴/s, consistent with unity quantum yield. The ultrasharp linewidth resolves exciton fine-structures (dark and triplet excitons) and their dynamics under a magnetic field. Additionally, b-PQDs can be electrically driven to emit single photons with 1 meV linewidth and photon-antibunching (g²(0)=0.4). These results pave the way for on-chip, low-cost single-photon sources for next generation quantum optical communication and sensing.

Copper halides are non-toxic, optically active semiconductors that can form various structural dimensionalities and dimensions. In this research, we focus on 0D (Cs₃Cu₂I₅), and 1D (CsCu₂I₃) compounds based on copper-iodide complexes that show efficient broad emission in the visible range. We study these compounds both as bulk and as colloidal nanocrystals. It is known from the bulk that these compounds can change their dimensionality (0D↔1D), based on stoichiometry. We found that for colloidal nanocrystals, a reversible phase transition can occur simply by introducing a polar or non-polar dispersion medium. This phase transition is accompanied by a significant modification of the morphology from round nanocrystals for the 0D phase to micron-sized rods for the 1D phase. We explore this phase transition's reversibility and kinetics using different optical probes. In addition, we present a study of the excited-state processes associated with the broad emission in these compounds. Specifically, we studied the structural modifications associated with excited-state dynamics by synchrotron transient XRD. In these experiments, we optically pump a sample of colloidal nanocrystals with an ultra-fast laser and probe them with a pulsed X-ray beam at different delays. This method can record the transient powder X-ray pattern at a temporal resolution of ~100 ps.

In the quest for quantum dots (QDs) with “green” formulations, Cu-based ternary materials are emerging as promising alternatives to the well-known Cd- and Pb-based binary semiconductors, due to their promising photophysical properties - as the tunability of the absorption/photoluminescence spectra by tuning their size - combined with low toxicity.[1]

CuInS₂ QDs with selected size and morphology have been synthesized via high-temperature heat-up colloidal pathways.[2] A purification protocol was specially designed to enable the size selection of the QDs by exploiting their dispersibility in different solvents by fractional separation and centrifugation.[3] The process was closely monitored by a combination of laboratory X-ray diffraction and absorption/emission spectroscopies.

CuInS₂ is a I−III−VI₂ semiconductor with a direct band gap of 1.5 eV. It has tunable emission peaks ranging from 650 to 780 nm but has a low photoluminescence quantum yield. This can be improved using a core-shell CuInS₂/ZnS structure. CuInS₂ QDs have a broad absorption spectrum covering almost the entire visible light range and extending into the near-infrared region, making them suitable for many applications in energy harvesting, such as solar concentrators.

The first part of my work focused on studying the influence of the synthesis parameters (e.g. reaction temperature, growth time) on the optical properties. In the second part, I focused on characterising the structure and microstructure of samples of different sizes.

CuInS₂ bulk material crystallizes in the thermodynamically stable tetragonal chalcopyrite phase, in which Cu⁺ and In³⁺ atoms are arranged in ordered sites within the cation sublattice. The wurtzite phase, in which the two cations are randomly distributed within the cation sublattice, is stable at high temperature (> 1318K). At the nanoscale, chalcopyrite and wurtzite are the most identified phases [4-6] and few reports claim the identification of a zincblende-like structure.[7] However, an in-depth X-ray-based characterization of the phase stability, crystal structure and defectiveness of colloidal CuInS₂ QDs is presently missing.

In this contribution, we focus on these aspects by applying advanced, synchrotron-based high-resolution wide-angle X-ray Total scattering (WAXTS) techniques. X-ray data of CuInS₂ QDs in the size range 2-10 nm were collected at the Material Science beamline of the Swiss Light Source of the Paul Scherrer Institute, at the ID22 beamline of the European Synchrotron Radiation Facility, and at the Cristal beamline of the French national synchrotron facility. A thorough data reduction was performed to subtract the scattered intensity of extra-sample components (empty capillary, air, capillary filled with the solvent) and to account for absorption effects, according to a well-established protocol.

The structural and microstructural characterization of QDs was carried out by reciprocal space total scattering methods, combining WAXTS with small-angle X-ray scattering (SAXS) techniques, based on the Debye Scattering Equation (DSE).[8]

The development of detailed atomistic models to account for QDs preferential growth directions indicating anisotropic morphologies and the presence of stacking faults is presently ongoing. The results of these studies will be presented.

The presentation will review some recent results on the effect of carrier-lattice coupling, exciton complexes and strong lattice anharmonicity on the optoelectronic properties of halide perovskites and their nanostructures. The early theoretical prediction and experimental demonstration of screening of electron-hole interactions by charge carrier-lattice coupling in 3D perovskites, was crucial to explain why photocarrier collection is possible at RT and how solar cell architectures could evolve toward much thicker active layers. The evaluation of carrier-lattice or exciton-lattices coupling remain challenging due to the complexity of the lattice fluctuations, including both deterministic and stochastic motions, covering a wide range of frequency. The interplay of these fluctuations with the electronic degrees of freedom is further complicated by the presence of Rashba effects, quantum and dielectric confinement. A fully predictive and accurate description of all the optoelectronic properties of halide perovskites is highly involved, because it underpins the physics of exciton complexes, hot carriers, polarons and excitonic polarons.

Expanding fluorescence bioimaging into the second near-infrared spectrum (NIR-II, 1000-1700 nm) unlocks advanced possibilities for diagnostics and therapeutics, offering superior tissue penetration and resolution. Two-dimensional copper tetrasilicate (CTS) pigments (MCuSi₄O₁₀, M = Ca, Sr, Ba) are known for their brightness and stability, yet synthetic challenges have curbed their integration into bioimaging. Here, we introduce flame-spray-pyrolysis (FSP) as a versatile and scalable synthesis approach to produce ultra-bright, metastable CTS nanosheets (NS) by annealing multi-element metal oxide nanoparticles into 2D crystals through calcination or laser irradiation. Group-II ion incorporation shifts emission into the NIR-II range, with Ba_0.33Sr_0.33Ca_0.33CuSi₄O₁₀ peaking at 1007 nm, while minor Mg-doping induces a hypsochromic shift and extends fluorescence lifetimes. The engineered CTS achieve quantum yields up to 34%, supporting NS high-frame-rate imaging (>200 fps). These unique properties enable CTS-NS to serve as powerful contrast agents for super-resolution NIR bioimaging, demonstrated in vivo through transcranial microcirculation mapping and macrophage tracking in mice using diffuse optical localization imaging (DOLI). This pioneering synthesis strategy unlocks wavelength-tunable NS for advanced NIR-II bioimaging applications.

iNSyT Technologies is a spin-off from LMU Munich developing advanced optical microscopy tools for real-time, single-particle analysis. The talk will be given by the company’s CEO, Dr. Mohsen Beladi, and will introduce for the first time iNSyT’s dual-mode platform. Designed for operando studies, the system captures nanoscale dynamics in quantum dots (QDs) and nanomaterials at unprecedented resolution and speed. The presentation will highlight how this technology enables new insights into heterogeneity, surface interactions, and fast transformations at the single-particle level, paving the way for deeper understanding in energy, catalysis, and nanoscience.

By capturing dynamic behaviors in real-time without disrupting the material or the process, iNSyT provides transformative insights into processes like catalytic water splitting, battery charging cycles, semiconductor corrosion, and light conversion in solar cells. With this level of precision, iNSyT enables scientists and industries to unlock the full potential of materials, accelerating breakthroughs and pushing the boundaries of what’s possible.

Photon echo spectroscopy overcomes the significant inhomogeneous broadening of approximately 16 meV in bulk mixed-halide perovskite FA_0.9Cs_0.1PbI_2.8Br_0.2 [1], revealing a much narrower homogeneous linewidth of about 16 μeV. This enables direct measurement of the fine structure splitting of excitonic states, arising from the Zeeman effect in an external magnetic field and electron-hole exchange interactions. These splittings manifest as oscillations in the time-resolved photon echo signal, caused by quantum beats between coherently excited exciton states. In Voigt geometry, the applied magnetic field induces mixing between bright and dark exciton eigenstates, allowing us to address and measure the splittings between all four excitonic states. By systematically varying the magnetic field strength and orientation, and combining this with polarization-sensitive excitation and detection, we extract electron and hole g-factors of g_e=3.4 and g_h=−1.0, respectively, and determine a zero-field splitting of 0.5 meV between the bright (J=1) and dark (J=0) exciton states.

The movement of excitons – bound electron-hole pairs – and free charge carriers in semiconductors is central to the operation of optoelectronic devices. Over the past several years, time-resolved optical microscopy has emerged as a powerful experimental technique for studying the spatiotemporal dynamics of charges and excitons in emerging semiconductor materials under a variety of experimental conditions. In this talk, I will present recent progress using time-resolved photoluminescence microscopy to understand charge and exciton transport in halide perovskite materials. I will introduce the technique and its history, review successes and failures, and efforts to benchmark time-resolved microscopy data against other techniques (e.g. Hall effect, FET mobility). Finally, I will present our findings in halide perovskites, including 1) temperature-dependent transition between free carrier and exciton-dominated transport in bulk halide perovskite crystals, 2) effect of A-site cation and grain boundaries, 3) anomalous exciton transport phenomena at cryogenic temperature, and 4) exciton transport in perovskite nanocrystal solids and nanocrystal superlattices.

Two-dimensional (2D) lead halide perovskites have emerged as promising materials for optoelectronic applications, particularly in achieving tuneable photoluminescence across the visible spectrum. Recent advances in precise dimensionality tuning have shown that controlled monolayer configurations of these materials can be engineered to achieve specific blue spectral emission, thereby expanding their utility in next-generation light-emitting devices. Understanding the excitonic features of these 2D materials is here crucial for optimizing their performance, and a theoretical framework using many-body perturbation theory provides a way to describe the interactions in these systems. Here, a Bethe-Salpeter equation approach provide the absolute energies of the electron and the hole, together with their mutual interactions. We employ a model Bethe-Salpeter equation (mBSE) with dielectric-dependent hybrid functionals to accurately model the excitonic properties of 2D lead halide perovskites and compare with optical response in 2D perovskites experimentally prepared in our laboratory. This approach incorporates a Coulomb kernel within the Fock exchange term, allowing us to capture the many-body effects inherent in the exciton dynamics. By leveraging a model dielectric function, we refine our results and achieve enhanced predictive capability regarding the theoretical optical properties of these materials with respect to the experimental values. Our findings confirm that manipulating dimensionality not only influences band structure in these low dimensional systems but also significantly alters the excitonic behaviour, underscoring the importance of using the appropriate level of theory to capture the experimental response when engineering efficient blue light-emitting devices based on 2D perovskites. This work paves the way for further exploration of 2D perovskites in various optoelectronic applications, positioning them as promising materials in the quest for high-performance, tuneable light sources.

Broadband near-infrared (NIR) emitting phosphors have attracted considerable attention in food, bioimaging, night vision, and plant lighting. However, NIR phosphors targeting the absorption of far-red/phytochrome (PFR) have rarely been reported. We note that gallium garnets are more suitable for satisfying the photomorphogenesis needs of plants. Accordingly, we have designed a Cr3+-doped Gd2.4Lu0.6Ga4AlO12 NIR phosphor from original Gd3Ga5O12:Cr3+ by substituting the large Gd3+ and Ga3+ ions with small Lu3+ and Al3+ ions to regulate relative energies and sequence of the two lowest excited states 2Eg and 4T2g. The optimal Gd2.4Lu0.6Ga3.87AlO12:0.13Cr3+ sample exhibits greater spectral overlap with the absorption of PFR, originated from the raised peak emissions and the blue-shift of emission band. Meanwhile, the luminescence is greatly enhanced by 2 times when the flux of H3BO3 was added during the synthesis. Thanks to the excellent EQE and low thermal quenching behavior, a NIR pc-LED was fabricated by integrating the Gd2.4Lu0.6Ga3.87AlO12:0.13Cr3+,3 wt%H3BO3 on a blue chip-on-board chip, which has a high output power of 505.99 mW and photoelectric efficiency of 11.24% at 300 mA. To further evaluate the potential of this device for plant growth, pea seedlings (Pisum sativum L.) as the model was investigated. The difference is achieved the 79.84% and 67.72% in dry and fresh weight under different treatments. This study provides a reference to regulate the spectral profile of Cr3+-doped NIR phosphors and sheds light on the practical application of Cr3+-doped NIR phosphors in the field of plant lighting.

Manganese (Mn) doping in metal-halide perovskites presents a promising strategy for tuning their optoelectronic properties. The incorporation of Mn²⁺ ions introduces a well-defined optically active energy level within the bandgap of violet- and blue-emitting perovskites, resulting in dual emission: one originating from the perovskite band edge and the other from the Mn²⁺ dopant states (⁴T₁ → ⁶A₁ transition). This unique emission behavior enhances the photoluminescence quantum yield (PLQY), facilitates rapid exciton diffusion, and improves the material's stability.

In this presentation, I will discuss the optoelectronic properties of highly luminescent Mn²⁺-doped two-dimensional (2D) Ruddlesden–Popper (RP) lead bromide hybrid perovskites. In particular, I will focus on how variations in organic spacer ligands (L) and layer thickness (n) influence the light-emitting characteristics of these materials. In addition, I will also examine the charge transport properties, specifically exciton diffusion, of these perovskites by correlating them with crystal rigidity and electron–phonon coupling strength. Finally, I will demonstrate the potential of these doped perovskites for white light-emitting diode (WLED) applications.Thus, this talk aims to provide deeper insight into the structure–optical property relationships in Mn-doped 2D perovskites, offering a foundation for the rational design of next-generation luminescent materials.

Pending

Most of current metal halide materials, including all inorganic and organic-inorganic hybrids, are crystalline materials with poor workability and plasticity that limit their application scope. Here, we develop a novel class of materials termed polymeric metal halides (PMHs) through introducing polycations into antimony-based metal halide materials as A-site cations. A series of PMHs with orange-yellow broadband emission and large Stokes shift originating from inorganic self-trapped excitons are successfully prepared, which meanwhile exhibit the excellent processability and formability of polymers. The versatility of these PMHs is manifested as the broad choices of polycations, the ready extension to manganese- and copper-based halides, and the tolerance to molar ratios between polycations and metal halides in the formation of PMHs. Additionally, we leverage the “structural tolerance” of PMHs to integrate two distinct coordination units of a single metal into a material, thereby achieving highly tunable optical properties in single-phase metal halides. The merger of polymer chemistry and inorganic chemistry thus provides a novel generic platform for the development of metal halide functional materials.

While solution-processed methods have driven much of the progress in halide perovskite research, their integration with silicon-based semiconductor platforms remains challenging due to issues of compatibility and process scalability. In contrast, vapor-phase growth offers a scalable, solvent-free approach that is inherently more compatible with semiconductor industry standards, while also providing precise control over interfacial structure, strain, and crystallographic orientation. In vapor-grown systems, the interface between the perovskite and the substrate is critical in determining phase formation, growth direction, and optical properties. In this work, we demonstrate that by carefully tuning vapor-phase growth parameters, we can control the geometry and orientation of CsPbBr₃ microwires, including the formation of angled out-of-plane wires.

By tuning substrate and growth conditions, we obtain two distinct microwire geometries: in-plane wires, which grow flat and aligned with the substrate, and out-of-plane wires, which emerge at a fixed angle relative to the surface. The in-plane wires exhibit well-faceted, rectangular prism morphologies, while the out-of-plane wires consistently grow at an angle of 57° ± 3°, as determined by angle-resolved cathodoluminescence. This angle corresponds to growth along the [100] direction with the {111} CsPbBr₃ facet at the substrate interface. Additionally, we report room-temperature lasing from the wires under nanosecond pulsed excitation. These wires show high emission efficiency and intense linear polarization, approaching 100% degree of polarization.

Additionally, we analyze and explore the role of competing Cs₄PbBr₆ phases, which act as nucleation seeds for CsPbBr₃ growth. We spatially resolve emission and lifetime properties across the interfaces using cathodoluminescence microscopy, revealing how the seed influences the emission characteristics. Our results resonate and support previous observations of similar heterostructures that were grown under very different growing conditions, indicating the generality of the observed effect and robustness of the measurement technique. 

 Together, these results offer new insights into the microscopic origins of light emission in halide perovskites and establish design rules for tailoring optical behavior through growth-controlled morphology and interface engineering.

Semiconductor nanocrystals, offering a market volume exceeding 5 billion Euros annually, have attracted great interest in quality lighting and displays. Such colloidal semiconductors enable enriched color conversion essential to superior lighting and displays. These colloids span different types and heterostructures of semiconductors from colloidal quantum dots to wells. In this talk, we will focus on atomically flat, tightly confined, quasi-2-dimensional wells, also popularly nick-named ‘nanoplatelets’, particularly for use in lighting and displays [1-14]. Also, we will present a powerful, large-area, orientation-controlled self-assembly technique for orienting these quantum wells either all face down or all edge up and demonstrate three-dimensional constructs of their oriented self-assemblies with monolayer precision [8,9]. Among their extraordinary features important to applications in lighting and displays, we will show record high efficiency from their colloidal LEDs [10,11] and record high gain coefficients and record low lasing thresholds from their colloidal laser media [1,12,13] using their heterostructures [2-6,10] and/or oriented assemblies [8,9,11].  We will finally discuss the use of colloidal quantum wells intimately integrated into metasurfaces to make a new class of colloidal meta-devices [14]. Given their current accelerating progress, these solution-processed nanocrystals hold great promise to challenge their epitaxial thin-film counterparts in semiconductor optoelectronics.

Luminescent metal halides are attracting growing attention as scintillators for X-ray imaging in scientific research, safety inspection, medical diagnosis, etc.; however, their decay time is too long due to B-site cations confining to ns², d^5, and d¹⁰ metals. Here we design a family of lead-free Eu(II)-based hybrid perovskitoids with spin-allowed 5d-4f bandgap transition emission toward simplified carrier transport during scintillation process. The experimental and theoretical analyses verify that the electron-phonon coupling therein is suppressed via symmetrical structural parameters as confirmed by the low Huang–Rhys factor, and thus diminishes the homogeneous broadening of the emission bandwidths. Moreover, the 1D/0D structures with edge/face-sharing [EuBr₆]^4- octahedra further contribute to lowing bandgaps and enhancing quantum confinement effect, enabling efficient scintillation performance. We demonstrate the X-ray imaging applications potentially in medical diagnosis, industrial inspection, and security. Our results pave the way for developing low-dimensional rare-earth-based halides for optoelectronic applications.

Despite the excellent performance of hybrid organic-inorganic halide perovskites-based red and green light-emitting diodes (LEDs) with external quantum efficiencies (EQEs) ~ 25% and luminescence (L) ~ 10⁴-10⁵ cd/m²,^{[1, 2]} desired pure blue-emitters and corresponding LEDs (455-465 nm) still suffer from low efficiencies and show inferior stability. In fact, most of the efficient blue-emitting perovskite LEDs reported so far exhibit emission in the sky-blue region (470-490 nm) with a maximum EQE of up to 20%^[3]; however, such emissions are inappropriate for desired high-quality display and white lighting applications. Moreover, spectral instability in mixed-halide perovskite blue LEDs remains a significant challenge that needs to be addressed to enable the development of fully perovskite-based lighting and display technologies. In this work, we present a set of innovative material design strategies aimed at enhancing both the photoluminescence quantum yields (PLQY) and stability of pure blue-emitting (~460 nm) perovskites through compositional and ligand engineering strategies. At first, we demonstrate the design of cesium lead halide (CsPb(Cl/Br)₃) nanocrystals (NCs) via the growth-on-substrate technique using molecularly engineered phenyl-based ligands and passivating additives, and they exhibit improved PLQYs with enhanced stability over 110 days. The resulting on-substrate grown pure blue-emitting NCs exhibit PL maxima ~ 460 nm with CIE chromaticity coordinates (0.14, 0.045), closely aligning with the desired blue emitters (0.131, 0.046) as defined by Recommendation 2100. Additionally, advanced PL microscopy measurements reveal that these compositionally-engineered NCs exhibit pronounced photo-enhancement and photostability with improved optical properties, attributed to reduced crystal defects and non-radiative traps owing to the high binding affinity of the molecularly engineered ligands. Furthermore, we demonstrate the design of pure blue LEDs utilizing these pure blue-emitting perovskites composed of various molecularly engineered cations, accompanied by device engineering strategies. We also conduct the spectral stability analysis of blue LEDs, examining both emission intensity and spectral shifts under varying operational conditions (vs Voltage and Time). Based on the composition and design/processing conditions, the pure blue-emitting materials and corresponding LEDs exhibit different spectral response, behavior/performance, and stability. Overall, our work presented here demonstrates effective design strategies for pure blue emitters, provides a detailed analysis of spectral stability and shifts in compositionally engineered blue-emitting halide perovskites and their corresponding LEDs, and offers a promising pathway towards the realization of stable pure blue emitters and high-performance pure blue LEDs.

Lead-halide perovskite nanocrystals are emerging as valuable platform for next-generation scintillators, capable of combining high light yield with sub-nanosecond timing while giving access to collective quantum-optical regimes. This presentation will outline a coherent research trajectory that begins with rational materials engineering and culminates in the observation of cooperative emission under ionising radiation. Recent work shows that integrating CsPbBr₃ nanocrystals into appropriately chosen high-Z or mesoporous hosts can suppress defect-mediated degradation, enhance charge-collection efficiency and preserve ultrafast radiative kinetics, thus overcoming the intrinsic limitations of colloidal emitters. Building on this foundation, weak quantum confinement gives rise to a giant oscillator strength that reconciles brightness and speed, historically conflicting figures of merit in radiation detection, while ordered superlattices enable scintillation superfluorescence, in which incoherent ionisation cascades converge into deterministic, picosecond bursts of light. Together, these advances demonstrate how interfacial chemistry, mesoscale ordering and many-body exciton dynamics can be orchestrated to convert stochastic electron tracks into coherent optical signals free from reabsorption and non-radiative losses. The resulting nanoscintillators deliver promising light yields with temporal resolutions approaching a few tens of picoseconds, setting the stage for time-of-flight imaging, high-energy physics instrumentation and precision dosimetry. The talk will distil the unifying principles that link materials design to emergent photophysics and discuss the remaining challenges for scalable device integration.

The short-wave infrared (SWIR) spectral region (900–1700 nm) plays a critical role in emerging applications such as remote sensing, active imaging, and NIR spectroscopy. These applications require high-power, spectrally tailored light sources that can operate efficiently and stably over long durations. However, conventional SWIR-emitting technologies — particularly InGaAs-based LEDs and lanthanide phosphors — are expensive, difficult to scale up, and offer limited flexibility in emission wavelength, hindering their deployment in compact or cost-sensitive systems. This demands high-power, cost-effective SWIR emitters.

Colloidal quantum dots (QDs), especially lead chalcogenide systems like PbS, offer a transformative alternative owing to their solution processability, spectral tunability, and compatibility with low-temperature fabrication. In this work, we present efficient and stable PbS QD-based downconverters designed for high-performance broadband SWIR emission. Using a cost-effective, room-temperature, all-solution process, we achieve downconverter films with precise control over quantum dot size and surface chemistry, enabling tailored emission across the SWIR spectrum.

The resulting downconverters exhibit photoluminescence quantum yields (PLQY) exceeding 30% and emission powers reaching up to 80 mW (~300 mW/cm²) under continuous optical excitation. We further demonstrate optical power conversion efficiencies of up to 12%, and exceptional spectral tunability. We also demonstrate a broadband downconverter with emission ranging from 1000 to 1600 nm and full width at half maximum (FWHM) exceeding 400 nm. This allows the creation of both narrowband and broadband SWIR emitters from a single platform.

Operational stability testing under constant illumination reveals robust device performance, with a T80 lifetime of approximately 200 hours at peak emitted power. These figures highlight the viability of PbS QD downconverters not only for fundamental studies of emerging emitter materials but also for practical deployment in low-cost SWIR sources.

This work underscores the potential of colloidal PbS quantum dots as scalable, wavelength-tunable alternatives to traditional SWIR emitters, offering a promising route toward affordable, efficient, and stable SWIR light sources for next-generation photonic applications.

The application of self-assembled molecules (SAMs) as selective contacts in optoelectronic devices has rocketed during the last four years due to the impressive enhancement in efficiency and the stability achieved in the devices containing SAMs. These SAMs are molecules of low molecular weight made of an anchoring group that form a covalent bond with the substrate, a linker that influences the molecular packing and ensures conductivity through the molecule and the terminal group. This terminal group is in direct contact with the emissive layer determining its packing and crystallization, also affecting the properties at the interface. Therefore, the composition of SAMs deeply influences the interfacial charge dynamics on the device under operational conditions which reflects in the performance and stability Moreover, SAMs form ultrathin layers. This means that the transmittance of the substrate does not vary significantly upon the addition of a SAM and that the amount of required material is low. In combination with the fact that SAMs can be deposited by dip coating or spin coating, the potential cost of the production of the devices can be lowered. For these reasons, SAMs are an excellent alternative to the traditional hole transport materials such as PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) or PTAA (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine), whose instability under operational conditions or its inherent acidity compromises the device stability.

SAMs have become well known as efficient hole selective contacts in perovskite solar cells and, to a less extent, in light emitting diodes (LEDs) prepared with perovskite nanocrystals. In all these cases, they contribute to the charge transport of holes between the electrodes and the photoactive layer. However, publications about their application as electron selective contacts in LEDs are infrequent. In this work, examples on the use of selected SAMs either hole or electron selective contacts in LEDs based on perovskite or CdSe/ZnS nanocrystals will be presented. In all cases, the molecular structure of the SAMs will be correlated with the morphologic and photophysical effects arisen at the interface with the emissive layer which translates to the performance of LEDs.

Chemically synthesized metal halide perovskite thin films and nanocrystals have emerged as a new class of efficient light emitting materials which are particularly interesting for development of light-emitting diodes (LEDs). Stability of perovskite-based LEDs is still an issue, which can be mitigated by choosing proper light-emitting layer, electron transport layer (ETL), and the interface design [1], as we demonstrated recently for FAPbBr₃ perovskite films with ultralow trap density in combination with ZnO ETL [2]. This design led to green perovskite light-emitting diodes with a brightness of ~312,000 cd m⁻², a half-lifetime of 350 h at 1,000 cd m⁻², and a power conversion efficiency of 15.6% at a current density of 300 mA cm⁻². As for many other nanocrystals, proper surface passivation is a key to ensure high colloidal stability and processability of perovskites, which can be achieved by choosing bidentate Lewis base ligands [3]. To avoid the use of toxic lead, CsSnI₃ perovskites can be implemented for efficient and rather stable near-infrared LEDs. The use of multifunctional hesperetin additive alongside the perovskite precursors allowed us to modulate the crystallization kinetics and inhibit the oxidation process of tin-based perovskite films. We demonstrated near-infrared CsSnI₃ perovskite LEDs with a peak at 948 nm, an external quantum efficiency of 4.7%, and a half-time of operation of over 11 h.

A major challenge in synthesizing infrared QDs has been the reliance on hazardous and heavy metal-containing materials like PbS and HgTe. InAs QDs are one of the most promising infrared emitting QDs as an alternative to heavy metal containing QDs. This study presents an improved synthesis method of InAs using tris(dimethylamino)-arsine (amino-As) along with Alane N,N-dimethylethylamine as a reducing agent and ZnCl₂ as an additive. The resulting InAs/ZnSe core/shell QDs, with a tunable shell thickness, exhibited photoluminescence around 900 nm and a photoluminescence quantum yield of up to 70%. Using these QDs, an LED was developed with an external quantum efficiency of 13.3% and a radiance of 12 Wsr⁻¹cm⁻² [1]. Long term stability of QD-LEDs under operation and also tunability of InAs QDs for longer wavelengths are two major challenges in recent years. This study presents our recent achievements on the improvement of the operation stability of QD-LEDs based on InAs and our optimization strategy for fast switching of LEDs for optical data transfer applications.

Colloidal semiconductor nanocrystals (NCs) have recently emerged as ideal triplet sensitizers owing to their diverse material composition and spectral tunability. However, the NCs that can efficiently sensitize near-infrared-to-visible photon upconversion remain largely limited to toxic lead-based NCs. Here, we present a new lead-free, near-infrared, indirect-bandgap sensitizer based on AgBiS2 NCs, enabling near-infrared-to-yellow upconversion with a quantum yield reaching 10.5% (normalized to 100%). The key to success is the precise stoichiometry control of AgBiS2 NCs, which provides the essential surface states for both radiative recombination and triplet energy transfer. Ultrafast transient absorption spectroscopy verifies the efficient triplet energy transfer mechanism mediated by surface states. Our work presents a new eco-friendly material system for efficient triplet fusion near-infrared photon upconversion. Furthermore, by leveraging the phonon coupling effect of AgBiS2, we were able to upconvert photons from the near infrared II region (980 nm) with an an effieciency of 6% (normalized to 100%).

Despite their relatively emerging degree of development, metal halide perovskite light-emitting diodes (PeLEDs) have reached outstanding brightness and radiative efficiency levels that roughly graze the maximum theoretical limits. Unfortunately, the complete understanding of their working principles and the photo-electrochemical mechanisms involved in the charge carrier injection/recombination dynamics are still a conundrum. Additionally, the strong ionic character of perovskites enables the migration of ions and the gradual formation of crystalline defects upon exposure to light and/or to an external electric field, which aggravates the complexity of these systems. In fact, these ionic processes are apparently coupled with those electrical involved in the generation of light and seem to be also connected with the widely reported limited long-term stability of the devices. Here, I will discuss the exploitation of a new methodology based on the combination of three frequency-domain modulated techniques, i.e. impedance spectroscopy (IS), voltage-modulated electroluminescence spectroscopy (VMELS) and current-modulated electroluminescence spectroscopy (CMELS), aimed at extracting values of characteristic thermodynamic constants and at reaching a full understanding of the PeLEDs technology. We propose a new theoretical model and an equivalent circuit that unifies these three techniques, which consider both the non-radiative and radiative contributions, as a powerful tool for the advanced characterization of any light-emitting device, being especially useful for the study of perovskite-based optoelectronic devices due to their inherent complexity. Particularly important is the deconvolution of the electrical, optical and ionic processes that are involved in the current-to-photon conversion, heat generation and/or degradation of the light-emitting material/device, as well as the elucidation of how all these phenomena mutually interact.

Today, quantum dots (QDs) are in high demand for display and LED applications. Many groups worldwide are advancing on‑chip QLEDs, electroluminescent QLEDs, and photoluminescent color‑filter organic LEDs (QOLEDs). Electroluminescent quantum‑dot LEDs combine high brightness, fast response, low operating voltages, exceptional color purity, and cost‑effective integration, and are poised to transform the display industry. As an alternative to pseudo-spherical 0-D QDs, 1-D quantum rods (QRs) have recently emerged as efficient, robust emitters in both photoluminescent (PL) and electroluminescent (EL) devices. Their dipolar emission—especially when transition‑dipole moments lie horizontally—enhances light out‑coupling, potentially boosting external quantum efficiency (EQE) by ~48%[¹]. Moreover, unidirectionally aligned QR films emit polarized light, improving display optical efficiency and ambient contrast.

We have synthesized low‑Cd QRs via one-pot soft‑metal–catalyzed Cd²⁺→Zn²⁺ exchange, achieving narrow‑band emission tunable across the visible spectrum, near‑100% PL quantum yield, and excellent thermal stability. In down‑conversion white LEDs, it delivers >120 000 nits brightness and cover 92% of the BT2020 gamut, with a record luminous efficacy of 149 lm/W[²]. Our QRLED display prototypes use cal. ~300× less material than conventional QD color‑conversion films. Furthermore, using optimized liquid‑crystal‑like ligands and combination of photo‑alignment/lithography process, for the first time, we engineered red and green luminescent color filters that emit polarized light (DOP ≈ 0.65), enhancing LCD contrast under ambient lighting[³].

For EL devices, we tailored a gradient QR shell with minimal thickness and reduced Zn content, paired with short organic ligands to lower injection barriers. A proposed bilayer hole‑transport layer increases hole injection while suppressing electron leakage, achieving optimal charge balance. These optimizations yielded record EQEs of >24% at ultrahigh brightness. We showed the first green-emitting QRLEDs that exceed 500 000 cd/m² brightness and maintain T₅₀ lifetimes over 16 000 h at 100 cd/m², making them highly attractive for next-generation high–color-gamut displays and lighting applications[⁴].

Highly transparent and large-area scintillator screen is highly desirable for next-generation X-ray imaging and detection, which is essential in the fields of medical diagnostics, industrial non-destructive testing, and security screening equipment, etc... Traditional scintillators, e.g., CsI-based single-crystal materials or garnet-type Y3Al5O12:Ce transparent ceramics, etc., are expensive and complex to prepare. Thus, low-cost synthesis technologies for large-area scintillator screen is highly appreciated. In this presentation, we will summarize our recent advances in the design, fabrication and applications of large-area scintillator screen by using the highly efficient hybrid metal halides luminescent materials. Our innovative researches included, but are not limited to, 1) we adopted the seed crystal induced cold sintering techiniques to prepare metal halide transparent ceramic scintillators; 2) we invented the preparation method of zero-dimensional (0D) luminescent metal halide hybrids glass and glass-ceramics as large-area X-ray scintillators. 3) we prepared the hybrid Cu(I)-based glassy cluster gel scintillator film by in-situ UV photopolymerization, and further presented a universal scheme to rapidly synthesize luminescent ionogels through the in-situ formation of 0D hybrid metal halides during the polymerization of monomer. Our innovative work in hybrid metal halides will be important for new type of scintillators with high transparency and excellent scintillation properties to meet the demanding requirements of high-resolution, large-area X-ray imaging.

Photon interconversion is a promising approach to increase the power conversion efficiency of photovoltaic devices. Downconversion of high energy photons can alleviate thermalization losses, while upconversion converts sub-bandgap photons to photons with a usable energy.

Here, we will focus on the upconversion process. To comply with energy conservation laws, the energy of two low energy photons is combined to form a single higher energy photon. For upconversion to be relevant for solar energy conversion, it must be efficient at low incident powers. In triplet-triplet annihilation the energy is stored in long-lived spin-triplet states, which enables efficient upconversion at solar-relevant powers. Since the direct optical generation of triplet states is forbidden per selection rules, sensitizers are required to generate triplet states with high yields. Currently, triplet sensitizers span a broad range of material classes including metal-organic complexes, semiconductor nanomaterials, and bulk perovskite films.

I will present the current understanding of triplet generation at the bulk lead halide perovskite/organic interface and discuss the role of molecular aggregation and intermolecular coupling on the energy landscape underlying the upconversion process. To date, the ‘gold standard’ for solid-state NIR-to-visible upconversion (UC) is rubrene, which is in large part due to intermolecular interactions influencing the optical properties of the organic molecule – the triplet annihilator. Unfortunately, the triplet energy (T₁ = 1.14 eV) of rubrene is energetically not well matched with the 1.55 eV bandgap of the typically utilized formamidinium-rich perovskites, leading to a large inherent energy loss during triplet generation. To increase the achievable apparent anti-Stokes shift obtained during the upconversion process, annihilators with a higher triplet energy are desired. [1],[2]