Colloidal InAs nanocrystals have become a central Pb-free material platform for infrared harvesting, where their performance is ultimately dictated by the underlying chemistry that governs nucleation, growth, and electronic structure. This talk will explore how controlling precursor reactivity, surface coordination, and dopant incorporation enables predictable tuning of size, defects, and carrier polarity in InAs systems. I will introduce recent approaches that use post-synthetic dopants to modulate semiconductor polarity and energy levels, providing a chemical route to optimize band alignment and suppress dark current in solution-processed photodetectors. In parallel, I will discuss how machine-learning analysis of high-dimensional spectroscopic data reveals hidden reaction intermediates and growth pathways, offering mechanistic insight that is difficult to access experimentally. Together, these advances illustrate how data-driven discovery and molecular-level chemical design converge to establish a synthetic toolbox for achieving high-quality, infrared-responsive InAs nanocrystals. This chemistry-driven perspective points toward more efficient, stable, and scalable infrared photodetectors built entirely from solution.

Colloidal quantum dots (QDs) have become prominent classical and quantum light sources. Despite the rapid rise of novel QD materials, such as those made of perovskites, there is a vast potential to further progress in more conventional QD material, particularly metal pnictides. Despite successful commercialization, InP NCs still lack synthetic versatility and robustness, as seen, for instance, in the continued quest to replace a commonly used, pyrophoric, and expensive tris(trimethylsilyl)phosphine precursor. We have developed a solid-state, nonpyrophoric, and synthetically readily accessible acylphosphines as convenient phosphorus precursors for the synthesis of InP NCs [1]. The proposed acylpnictide route is anticipated to foster the development of other metal phosphide and metal arsenide NCs.

Colloidal III-V arsenide quantum dots (QDs) are promising low-toxicity, solution-processable materials for near-infrared optoelectronics, yet their development has been constrained by the scarcity of suitable precursors and proneness to oxidation. Existing routes either rely on highly reactive but toxic, pyrophoric group-14-substituted arsines, or on safer aminoarsines that require in situ reduction and cause staggered rather than a single burst nucleation. We introduce aluminum tris[bis(mesitoyl)arsenide] as a nonpyrophoric and air-stable precursor that, upon nucleophilic attack, directly delivers the formally As^3- species for producing InAs QDs [2].

The presentation will encompass the work of my interdisciplinary team and diverse international collaborators, whose names will be appropriately mentioned in the presentation and footnotes.

In this talk I will present recent developments on the synthesis and control of growth kinetics of InSb colloidal quantum dots. I will further dicuss their photophysical properties and finally present progress on devices, particularly infrared photodetectors. In the second part of the talk I will present about our efforts on InAs infrared CQDs, the synthetic approaches taken to cover the full SWIR range as well as the resultant optoelectronic devices i.e. LEDs and photodetectors.

In this talk, I will begin with recent developments focused on integrating infrared nanocrystal films for infrared imaging [1-2]. Although progress has been impressive, there is still room for improvement. Optical and electronic spectroscopy are often the bridge between materials and devices. Ultraviolet photoemission spectroscopy is widely used to access band alignment on an absolute energy scale, enabling rational choices of electrodes and charge transport layers to pair with a given optically active material.

Although powerful, this method relies on the assumption that the electronic structure of the pristine material remains largely unaffected during integration into a complex environment, despite changes in dielectric surroundings and the presence of applied electric fields. Consequently, there is a strong need for new tools capable of in situ and operando determination of the electronic structure [3].

In this talk, I will demonstrate how X-ray photoemission imaging can be employed to reveal the energy landscape of nanocrystal-based devices. I will present results applied to various geometries, showing how the method provides direct access to gate-induced energy shifts in field-effect transistors (FETs), enabling quantification of their arm lever [3], the in-plane vectorial distribution of the drain-source electric field [4], and the built-in potential of a diode [5]. Additionally, I will discuss how defects influence the operation of an FET and demonstrate that energy-induced modifications extend well beyond the geometric size of the defect.

Self-powered near-infrared (NIR) detection technologies attract immense interest both from scientific and industrial perspectives due to their vital applications in environmental monitoring, night vision, and imaging in remote locations. Solution-processed colloidal semiconductor nanocrystals (NCs) have been a centre of interest among third-generation devices, offering band gap tunability, strong quantum confinement, and lower cost and large-scale fabrication. Unfortunately, the dominant NC families employed in infrared (IR) detectors are based on toxic heavy metals, such as Cd, Pb, and Hg, which restrict their use in consumer electronics and biomedical technologies under the European RoHS regulation (Restriction of the Use of Hazardous Substances). To address this limitation, silver chalcogenide (Ag₂E, where E = S, Se, or Te)-based NCs have emerged as a promising class for near IR and short-wave IR detection, offering favourable bandgaps in the IR region (Ag₂S ~0.9-1.3 eV, Ag₂Se ~0.15 eV, Ag₂Te ~0.3 eV), making them appealing from health and environmental safety perspectives. However, most Ag2E NC-based photodetectors still rely on solid-state ligand exchange protocols because solution-phase ligand exchange often fails due to poor colloidal stability and surface degradation of NCs during the process. A major disadvantage of this method is that it requires multiple layer-by-layer processing steps, which increase fabrication time, material consumption, and can lead to non-uniform or low-quality films. Most attempts at Ag₂E NC solution-phase ligand exchange fail because the weak Ag–chalcogen surface bonds, which can easily be disrupted by polar solvents or reactive short ligands, lead to aggregation and/or loss of optical and electronic properties.

In this study, we report a versatile Ag₂S NC ink based on a solution-phase ligand exchange strategy that yields fully passivated, highly dispersible and stabile NCs compatible with direct deposition of functional device layers. We investigated the impact of this ligand engineering on the performance of Ag₂S NCs-based photodetectors fabricated on flexible textile substrates with asymmetric electrode by following our previous protocol.^1,2 Importantly, we prepared highly conductive films on flexible textile substrates by directly depositing Ag₂S NC ink without further chemical treatment. The devices fabricated demonstrate strong self-powered responsivity across the 400–1200 nm band with excellent mechanical flexibility (devices demonstrated excellent mechanical flexibility, maintaining high performance even after 500 bending cycles), enabling applications in continuous health monitoring, smart clothing, and night-vision technologies under the European RoHS regulations.

Perovskite based solar cells, using three-dimensional (3D) hybrid halide perovskites as the active layer reach high power conversion efficiencies (PCE), getting closer to the PCEs of the silicon technology. However, a key challenge to overcome is still the intrinsic and extrinsic instabilities of the 3D perovskites when exposed to temperature, moisture, oxygen and UV light. Thanks to properties like surface passivation, leading to a reduction of nonradiative recombination, or inhibition of ionic migration, remarkable achievements have been made on PCE and stability, using new cations and innovative architectures.

In this work, the absorbant material is the all-inorganic 3D perovskite CsPb(I,Br)₃, deposited by spin-coating or by slot-die coating. Due to the small size of the Cs⁺ cation, iodine Cs-based perovksites show phase unstabilities, so that chemical engineering is first performed to stabilize the black photoactive phase at room temperature. Then several strategies, involving low-dimensional materials, such as two-dimensional (2D) perovskites or perovskite nanoparticles, are explored to protect and passivate the CsPb(I,Br)₃ layers.

The deposition of the low dimensional perovskite layer, and its effect as a protective layer of the 3D perovskite, is characterized by using morphological (Scanning Electron Microscopy), structural (X-ray diffraction) and optical (photoluminescence, confocal microscopy) experiments. Both strategies demonstrated improvement of the material stability under high humidity.

Solar cells have been fabricated, using the architecture NIP, with and without the protective layers. Device efficiencies have been measured and show the beneficial effect of passivation at the interface perovskite / HTL. By indoor light cycling test, long-term durability under operational conditions has been evaluated and revealed promising long-term stability of the passivated devices, providing perspectives for the development of reliable and industrially viable technologies.

Metal halide perovskite nanocrystals (PNCs) have emerged as a versatile class of materials owing to their outstanding optoelectronic properties and facile solution processability. Achieving high crystallinity and long-term stability is essential for advancing their integration into high-performance optoelectronic devices. In our recent work, we have established a series of synthesis strategies to obtain phase-stable, low-defect PNCs across diverse compositions, including Pb-based, Sn–Pb alloyed, Sn-based, and lead-free double perovskite systems[1-12]. Comprehensive photophysical investigations—spanning steady-state and ultrafast spectroscopies—have enabled us to elucidate photoexcited carrier dynamics such as hot-carrier relaxation, carrier extraction, and recombination pathways, thereby clarifying the structure–property–device relationships in these materials[5,7,11].

A major focus has been the identification and engineering of defects that critically limit the performance of Sn–Pb alloyed and Sn-based PNCs[8-10]. Temperature-dependent static and transient absorption spectroscopy allows us to disentangle static disorder (defects and impurities) from dynamic disorder arising from carrier–phonon coupling. We find that static disorder primarily introduces band-tail defect states, whereas dynamic disorder governs bandgap renormalization; together, they dictate fast carrier trapping and slower band-to-band recombination dynamics. Atomic-resolution STEM imaging and first-principles calculations further reveal that antisite defects generate deep-level trap states, serving as dominant nonradiative pathways. In parallel, we elucidated oxygen-driven and solvent-driven oxidation mechanisms of Sn, which severely impede the development of Sn–Pb and Sn-based PNCs.

To overcome these limitations, we devised a synergistic antioxidation strategy combining tri-n-octylphosphine (TOP) with micron-sized Sn powder. This approach effectively suppresses Sn(IV) formation, reduces defect trapping, and alleviates lattice distortion, enabling high-symmetry α-phase CsSnI₃ nanocrystals with ultralong carrier lifetimes (>200 ns). When applied to Sn–Pb alloyed PNCs, this strategy increased the photoluminescence quantum yield to 35% and extended carrier lifetimes by nearly two orders of magnitude[8].

These insights provide critical design principles for developing highly luminescent, low-toxicity Sn-based perovskite nanocrystals, and they open promising pathways toward their practical implementation in LEDs, solar cells, and other next-generation optoelectronic technologies.

Lead halide perovskite nanocrystals (NCs), such as CsPbBr₃, are promising candidates for next-generation scintillators due to their ultrafast radiative kinetics and high emission efficiency [1]. However, their integration in composite scintillators is limited by poor compatibility with high-Z sensitizers, reabsorption losses at high loading, and low radiation stopping power due to their nanoscale dimensions [2].

Here, a robust strategy is demonstrated to hybridize CsPbBr₃ NCs with hafnium oxide (HfO₂) nanoparticles (NPs) as transparent, high-Z electromagnetic sensitizers. Surface oxygen dangling bonds on HfO₂ NPs are identified as the main source of perovskite degradation, and it is shown that a PbBr₂ pre-treatment effectively passivates these sites. This enables stable NC-NP hybrids, preserving optical quality and scintillation properties. Co-synthesis in the presence of treated HfO₂ NPs suppresses NC degradation and enhances both photoluminescence efficiency and thermal robustness. The hybrids can be embedded in polymer nanocomposites via thermal radical polymerization, a process typically detrimental to perovskites.

Under X-ray excitation, HfO₂ NPs significantly enhance radioluminescence intensity without compromising the ultrafast response of CsPbBr₃ NCs, confirming efficient electromagnetic sensitization via electron cascade.

This work offers a viable pathway for designing hybrid nanoscintillators with enhanced stopping power and stable optical performance for practical radiation detection technologies.

Auger recombination plays a pivotal role in the photophysics of colloidal quantum dots (QDs), limiting light-emission efficiency while also providing a pathway to generate and manipulate hot, unrelaxed carriers. When the Auger process is  sufficiently fast, it can enable efficient electron photoemission—a phenomenon attracting considerable interest for its potential application in technologies ranging from photomultipliers and night-vision devices to redox photochemistry, high-resolution electron microscopy, and free-electron lasers.

Since the electron affinity (E_a) in QDs is usually larger than the bandgap energy (E_g), promotion of an electron above the QD vacuum level requires at least two consecutive Auger steps, with the second step involving re-excitation of the hot carrier generated by the first Auger-recombination event. In conventional (undoped) QDs, however, this multi-step Auger photoemission process is strongly suppressed by competing energy losses through phonon emission, which causes rapid electron cooling before the second Auger  step can occur.

In 2019, we reported that ultrafast spin-exchange (SE) interactions in Mn-doped colloidal CdSe QDs lead to a dramatic enhancement of the Auger recombination rate, making it faster carrier cooling via phonons¹. This discovery enabled us to demonstrate highly efficient visible-light driven generation of solvated electrons using Mn-doped CdSe QDs dispersed in water², achieving quantum efficiency of up to ~3%.

While demonstrating its considerable potential for generating and manipulating hot carriers, SE Auger recombination remains poorly understood from a mechanistic standpoint. To address this gap, we recently carried out a detailed investigation of SE Auger recombination in a series of Mn-doped QDs with bandgaps tuned from below to above the energy of the Mn spin-flip transition³.

From these studies, we conclude that observation of ultrafast Auger recombination requires the formation of a hybrid multiexciton state composed of intrinsic QD excitons and Mn-based excitations. In this regime, Auger recombination proceeds via a cross-relaxation process mediated by strong Coulomb-exchange interactions involving two correlated spin transfers between the QD and an excited Mn ion. We find that the Auger rate depends solely on QD exciton occupancy, rather than on the number of excited Mn ions, and exhibits no size dependence —features unusual for conventional Auger recombination but fully consistent with an SE-driven process.

These findings resolve the long-standing puzzle of Mn-induced Auger decay acceleration and provide design principles for tailoring QD properties through energetic alignment and controlled magnetic doping.

Nonreciprocal optical behavior, the ability of a material to absorb or emit light differently depending on the direction of propagation, has traditionally required magneto-optical fields, complex metamaterials, or delicate nanophotonic architectures. Here we show that readily synthesized, solution-processed colloidal nanomaterials can intrinsically support nonreciprocal light–matter interactions when their chiral and linear anisotropies are engineered to interferometrically couple. Using the Stokes–Mueller formalism, we derive a compact analytical expression that identifies the conditions to produce nonreciprocal absorption and emission of orthogonal linear polarizations. We experimentally validate these predictions in thin films of CdS, CdSe, and CdTe magic-size clusters [1-4] whose comparable circular and linear dichroism provide an ideal platform for testing this theory. By tuning cluster organization and anisotropy, we direct the sign and magnitude of the nonreciprocal response and establish design rules for achieving directional polarization selectivity without external fields or structural asymmetry. These results broaden the fundamental photophysics of confined semiconductor nanocrystals, revealing that nonreciprocity can emerge in macroscopically isotropic, low-dimensional materials through purely optical interference. The ability to achieve direction-dependent polarization control in scalable quantum-confined films opens new avenues for device concepts spanning optical routing, polarization-multiplexed information processing, and compact logic elements, helping bridge fundamental nanomaterial physics with next-generation optoelectronic technologies

Colloidal quantum dots (QDs) have found commercial success in light-downshifting applications on the back of incredible advances in synthesis, shelling, and engineering. However, highly insulating shells are unsuitable for many optoelectronic applications, which resurfaces the challenge of ‘trap’-state emission—observed since the dawn of the field—and associated with diminished emissivity, anomalously large Stokes’ shifts, and worsened photochemical stability. The structural and chemical identity(ies) of these trap states remain unclear, in part due to the obscuring effect of ensemble-level studies. Here, we report the kinetics and dynamics of trap emission from individual, CdSe-based QDs. We find that individual QDs can intermittently display both band-edge and trap-state photoluminescence over time, while maintaining single-photon purity. The excited-state configuration(s) that is associated with trap emission appears to be distinct from an OFF-configuration (familiar from studies of blinking), demanding an expansion of existing models for the macroscopically time-dependent photophysical behaviours of QDs. We observe that the decay kinetics of trap emission are persistently slower relative to the band-edge—phenomenologically consistent with an excited-state reservoir, rather than a quenching center. Moreover, in periods where trap emission is observed, the band-edge photoluminescence slows, consistent with delayed emission following recycling. Ultimately, we can quantitatively capture the time-averaged and macro-time-dependent photophysics of each QD with a simple kinetic model based on reversible equilibration between band-edge and trap states and a macro-time-varying energetic offset. This supports the key conclusion that the state that gives rise to this trap emission lies shallow within the gap and is energetically dynamic on individual QDs over macroscopic timescales that are consistent with photoinduced structural changes. We discuss implications with regards to trap-state identity(ies).

Colloidal quantum dots (QDs) are often exploited in an ensemble (e.g., as films) making use of their high photoluminescence efficiency and color tunability. Nonetheless, QDs present desirable properties at the nanoscale too, for example: a QD acts as a single-photon emitter, or it can be used for other localized phenomena. Despite this, single QDs present challenges in terms of manipulation. In addition, much like large size optoelectronic devices (> 1 mm), at the nanoscale, light out-coupling and control is of paramount importance. In fact, a vast literature discusses single QDs coupled with on-substrate photonic nanostructures such as antennas, micro-cavities, and waveguides, to impart either directionality, wave polarization or enhance the rate of photon emission. In this talk, I will discuss how large oxide shells (e.g, SiO₂, TiO₂, etc…) grown around single QDs can be employed to enhance their manipulation at the nanoscale and modify their emission properties. Through a combination of synthetic methods developed via a design-of-experiment approach,¹ large SiO₂ (diameter > 300nm) nanoparticles embedding a single QD are grown and then used for fabricating single photon emitter arrays² or monolayers through capillary assembly. The large oxides shells also enable control over the emission of single QDs, modifying the emission wavelength and rate. Finally, the large shells can be employed as a scaffold to grow additional nanostructures, enabling a further degree of functionalization of the embedded QD.

The fluorescence spectra of individual semiconductor nanocrystals (NCs) can inform on key physical properties such as the emission pathway and dephasing mechanisms [1,2]. However, structural variations between individual particles broaden the ensemble fluorescence spectrum. This broadening obscures the single-NC lineshape and complicates efforts to understand key photo-physics [3]. Practically, understanding the degree of optical heterogeneity within a sample also benefits efforts to use NC materials in light-emitting diodes (LEDs) [4] and lasing [5].

Today, the standard technique for the determination of single-NC emission properties and optical heterogeneity is single-NC spectroscopy [1]. While powerful, this approach can suffer from user selection bias and low statistical significance. In addition, single-NC measurements typically require very photostable samples. To address these deficiencies, we introduce a novel photon-correlation technique that extracts single-NC emission spectra from a solution ensemble with high statistical rigor. Unlike other ensemble-level photon-correlation [6] or nonlinear techniques [7], our method is able to accurately resolve asymmetric spectra and identify sub-populations of emitters.

In this work, we first derive the theoretical connection between the measured intensity fluctuations and the single-NC spectrum. Next, we computationally model the experiment as a proof of concept. Then we construct the experimental optical setup and apply the measurement to a solution ensemble of red-emitting InP/ZnSe/ZnS NCs. Our measurement reveals a high degree of optical heterogeneity in the sample. Comparison of these results with other single-NC measurements provides experimental verification of our new technique. Finally, we use the new method to analyze a sample of lightly doped ZnSe_1-xTe_x /ZnSe/ZnS NCs, a candidate material for blue quantum dot LEDs. We observe the presence of multiple spectral populations within the ZnSe_1-xTe_x ensemble, which we attribute to separate distributions of excitonic and trapped emitters. Our results will inform future synthetic efforts to optimize ZnSe_1-xTe_x NCs for commercial displays. More broadly, our results highlight the ability of the new technique to efficiently and accurately characterize samples of nanoscale emitters.

Copper sulfide (CuS) semiconductor nanoparticles exhibit localized surface plasmon resonances in the near-infrared (NIR) range via vacancy-induced charge carriers [1], enabling plasmon-assisted enhancement of photoluminescence of quantum dots (QDs) [2]. Periodic plasmonic structures can simultaneously raise excitation fields [3], increase radiative decay rates (via Purcell effect) [4], and decouple emission into well-defined angles via hybrid plasmonic modes. Periodic metal plasmonic nanostructures [4-6] as well as lithography-processed Si-based metasurfaces [7] are reported to enhance and direct the spontaneous emission of NIR QDs. An alternative approach for metasurfaces preparation is laser interference lithography [8], which allows scalable and reproducible grating fabrication for controllable directional light extraction from nanoparticle arrays.

In this work, we designed a mask‑compatible CuS semiconductor stripe grating that can enhance and redirect NIR (800–1300 nm) QD emission. CuS hexagonal nanoplatelets were densely packed into stripes with a period of 600−900 nm, thickness of 40 nm, and width of 90 nm on a glass substrate. The particles were first drop-cast from their concentrated colloidal solution and then were shaped into regular stripes on top of a 10 nm thick CuS nanoparticle layer with the use of a soft polydimethylsiloxane mask. The grating morphology was investigated with atomic force microscopy. For simulations we used Ansys Lumerical FDTD software with periodic Bloch boundary conditions for in‑plane symmetry and perfectly matched layers above and below the structure. Plane‑wave excitation was used with polarization oriented across the stripes and monitors were placed before and after the structure to collect its reflection and transmission power, respectively. Field maps around stripes demonstrate the enhancement of electromagnetic field distribution around the structure. Simulations predict lattice–assisted plasmon resonance hybridization with 2–5-fold radiative‑rate enhancement and more than 3-fold local field enhancement due to efficient coupling.

Photoexcitation of low-dimensional semiconductors can lead to the formation of strongly confined but losely bound electron-hole pairs, or weakly confined but strongly bound excitons. Reference systems for both limits are 0D CdSe quantum dots and 2D CdSe nanoplatelets. In this presentation, we discuss examples of low dimensional systems characterized by strongly bound excitons. After a survey of exciton properties using CdSe nanoplatelets as an example, we first present the photophysics of excitons and bi-excitons in CsPbBr3 nanoplatelets. In these materials, strong electron-phonon coupling results in significantly different properties as compared to CdSe nanoplatelets, with major impact on the prospects of such materials for optical amplification and lasing. Next, we move the spherical ZnSe nanocrystals. We provide evidence that these materials are best understood as excitonic rather than strongly confined. However, opposite from CdSe nanoplatelets, a sizeable Stokes shift reduces spectral overlap between exciton absorption and emission, which leads to net optical gain from exciton recombination. We demonstrate that this characteristic leads to lasing under nanosecond optical pumping, with a record-low threshold and high optical efficiency. Based on these different examples, future directions in exciton-based low-dimensional materials are discussed.