Indium phosphide-based quantum dots (QDs) are leading Cd- and Pb-free alternatives for photonic applications spanning 400-920 nm. However, their long-term photostability under prolonged illumination remains poorly understood. In this study, we systematically investigate the optical response of colloidal InP/ZnSe/ZnS core/shell/shell QDs exposed to white light under a dynamic inert atmosphere (glovebox filled with circulating N2 with O2 < 0.1 ppm, H2O < 1.0 ppm). Upon illumination, the QDs exhibit irreversible photodarkening, defined as a reduction in photoluminescence quantum yield with a nearly unchanged absorption spectrum. Photodarkening shows a linear dependence on absorbed photon dose, with photoexcitation deep into the conduction band inducing it more rapidly than resonant photoexcitation. Additionally, prolonged photoexposure leads to an emission redshift and an enhanced delayed-emission component, consistent with the selective photodarkening of individual QDs. Experiments in air and controlled humidity (10% and 90% relative humidity) indicate that photodarkening primarily arises from photooxidation by oxygen, whereas water promotes QD photoetching. This is further corroborated by control experiments in which the QDs are illuminated under dry oxygen (<3 ppm of H2O) and in a cuvette sealed by fusion under a N2 atmosphere with <0.1 ppm of O2 and <1 ppm of H2O. These experiments show that photodarkening does not occur in QDs contained in the fusion-sealed cuvette, while under dry oxygen the photodarkening rates of the QDs are even faster than in dry air. These findings advance understanding of InP-based QD photodegradation and provide a framework for quantifying their stability under light stress.

The impact of partial shading on the light distribution and associated efficiency reduction on side-mounted solar cell strips in square luminescent solar concentrators (LSCs) is investigated. Combining experimental testing and ray-trace model simulations the effects of partial shading on the LSC electrical performance were assessed at different locations of the LSC waveguide and proximity relative to the solar cell strip. It was found that electrical performance was affected in a non-linear manner: shading closer to the solar cell strip resulted in a significant reduction in performance with variations depending on the location, while shading further away led to a less severe decrease in conversion efficiency. For an LSC with four side-mounted solar cell strips, it is found that shading at the center of the LSC waveguide results in higher efficiency compared to shading at the edges or corners. This can be explained as central shading affects all solar cells strips uniformly, thus reducing the mismatch in photogenerated currents in the solar cell strips. Conversely, corner shading resulted in the lowest efficiency due to the direct disruption of photogenerated currents in multiple solar cell strips simultaneously. A photon distribution analysis from ray-tracing confirmed that shading near the edges of the LSC leads to local reductions in photon numbers, while central shading disrupts light distribution more uniformly across an LSC with four solar cell strips.

Copper indium sulfide (CIS) quantum dots are emerging as promising materials for solar cells, deep-tissue bioimaging, and light-emitting devices, due to their inherently lower toxicity and excellent photoluminescence properties. However, they typically exhibit a broad emission linewidth (-300 meV), making them lack of color and single-photon purity and thus less competitive with prototypical Cd-based nanocrystals. Herein, we report a strategy to narrow down the emission linewidth of CIS quantum dots from - 300 meV to - 120 meV via manipulation of Zn-alloying. The spectral narrowing was firstly observed in the epitaxial overgrowth of ZnS shell on the hexagonal wurtzite CIS quantum dots. Initially, the products exhibit two emission bands, a broad emission with linewidth of - 300 meV and a narrow emission with linewidth of - 120 meV. The broad emission is attributed to the recombination of a delocalized conduction band electron with a Cu-related localized hole, while the narrow emission originates from the band-edge exciton. Spectroscopic and structural analysis indicate that Cu+ for Zn2+ cation exchange prior to heteroepitaxial overgrowth of a ZnS shell is the key factor to promote the narrow emission, likely by suppression of hole localization on Cu+-sites. Precise manipulation of the Zn-alloying in CIS cores leads to a symmetric single band-edge emission with a photoluminescence quantum yield as high as - 35% at 670 nm and linewidth as narrow as 120 meV. These nanocrystals are integrated into light-emitting devices, which exhibit a high turn-on voltage of 4.5 V and maximum radiances reaching over 1000 cd/m2.

This study focuses on the development of environmentally friendly Au-Cu2-xS/CuInS2 heteronanotrimers. The chosen strategy relies on the laser photodeposition of a single gold nanodot (ND) onto Janus Cu2-xS/CuInS2 heteronanocrystals (HNCs). This method offers precise control over the number, location, and size (5 to 8 nm) of the Au NDs by adjusting laser power for the career production, concentration of hole scavenger for charge equilibration in redox reactions, and gold precursor concentration, and exposure time for the final ND size. The photoreduction of gold ions onto HNCs starts systematically at the Cu2-xS tip. The Au deposition then depends on the CuInS2 segment length. For short HNCs, stable Au-Cu2-xS/CuInS2 heteronanotrimers form, while long HNCs undergo a secondary photo-induced step: the initial Au ND is progressively oxidized, with concomitant deposition of a second gold ND on the CuInS2 side, to yield Au2S-Cu2-xS/CuInS2-Au heteronanotrimers. Results are rationalized by quantitative comparison with a model that describes the growth kinetics of NDs and Au-Cu2-xS transformation and emphasizes the importance of charge separation in predicting selective deposition in heteronanotrimer production. The key parameter controlling Au-Cu2-xS/CuInS2 HNCs is the photoinduced electric field gradient generated by charge separation, which is tailored by controlling the CuInS2 segment size.

Quantum dot (QD)-based luminescent solar concentrators (LSCs) promise to revolutionize solar energy technology by replacing building materials with energy-harvesting devices. However, QDs degrade under air, limiting the long-term performance of QD-LSCs. This study introduces an innovative approach to prevent QDs degradation by utilizing a photoactive polymer matrix (maleic anhydride-grafted poly(styrene-b-ethylene-co-butylene-b-styrene, SEBS-g-MA). This strategy has been tested outdoors over a 2-year period on five LSCs, followed by characterization of the weathered devices. The tested LSCs consist of three QD-LSCs (CuInS2/ZnS, InP/ZnSe/ZnS, CdSe/CdS/ZnS core/shell QDs), alongside a Lumogen dye-based LSC and a luminophore-free LSC. The study yields several findings: 1) SEBS-g-MA undergoes photochemistry outdoors, 2) SEBS-g-MA accelerates the photodegradation of Lumogen, 3) the power conversion efficiency of CdSe-based QD-LSC drops by 80% due to reduction of the photoluminescence quantum yield, and 4) under illumination SEBS-g-MA protects CuInS2 and InP-based QDs from degradation, ensuring a stable performance during the entire study. This work thus demonstrates for the first time that the interaction between the luminophores and the matrix is a critical determinant of the long-term success of LSCs. Leveraging on the fact that this is the longest outdoor study to date, we propose design rules for highly efficient and stable QD-LSCs.

The essential feature of nanomaterials is that their physical and chemical properties are size dependent, making it possible to engineer the material properties not only by defining its chemical composition, but also by tailoring the size and shape of the nanostructures, and the way in which individual building blocks are assembled. This chapter addresses the origin of the size dependence of the properties of nanomaterials, which can be traced to two fundamental nanoscale effects: (a) the increase in the surface/volume ratio with decreasing size, and (b) spatial confinement effects. Furthermore, the definition and classification of nanomaterials is introduced, and the techniques used to fabricate and study them are briefly discussed, with emphasis on nanoparticles of inorganic materials.

The realization of a net-zero energy built environment is challenging, especially in dense city centers with highrise buildings. While in suburban residential areas, roof space in combination with efficient solar photovoltaics (PV) can lead to energy self-sufficiency, for high-rise buildings this is only potentially possible if all fa¸cades are also harvesting solar energy. For aesthetic and occupational health reasons, PV fa¸cades should be (partly) transparent and color-neutral. Solar energy harvesting windows based on luminescent solar concentrators are one class of transparent PV that combines transparent waveguides concentrating light on their sides where solar cells are mounted. A compromise between color-neutral transparency and harvesting efficiency must be found, leading to average visible transparency values of >70%, color rendering index >80, and efficiencies of 2-3%. A range of luminescent species embedded in the waveguide has been investigated, from organic dyes to nanoparticles based on chalcogenides and perovskites, while combinations of those are investigated as tandem structures. This contribution will review recent experimental and simulation results, and will derive promising strategies to approach a theoretical limit of 20% color-neutral transparent efficient luminescent solar concentrators, which is based on full utilization of the UV/blue and the red/IR part of the solar spectrum, with limited utilization of the visible part.

Three quantum dot luminescent solar concentrators (QDLSCs) are constructed to assess their performance in an outdoor environment over an entire year. The QDLSCs have a PMMA‐Kraton‐PMMA sandwich structure with either InP/ZnSe/ZnS, , or CdSe/CdS/ZnS core/shell quantum dots incorporated in the Kraton interlayer. Furthermore, two reference LSCs are included: one using Lumogen F Red 305 as the luminophore and one without a luminophore in the Kraton layer. The power conversion efficiency is assessed for a cloudy and a sunny day, showing the influence of diffuse and direct irradiance. Moreover, the influence of mounting orientation and direct irradiance is analyzed for individual solar strips attached to the sides. Long‐term results show an efficiency increase of and InP/ZnSe/ZnS QDLSC while the CdSe/CdS/ZnS QDLSCs and the Lumogen LSC show a pronounced drop in efficiency in the first 3 months. Photodegradation studies under continuous white light exposure for 420 h are performed on smaller pieces cut from the QDLSCs before their assembly outdoors and show similar trends to those observed in the 1 year outdoor study. Future research will focus on the postmortem analysis of the QDLSCs and increasing the efficiencies.

Incorporating magnetic ions into semiconductor nanocrystals has emerged as a prominent research field for manipulating spin-related properties. The magnetic ions within the host semiconductor experience spin-exchange interactions with photogenerated carriers and are often involved in the recombination routes, stimulating special magneto-optical effects. The current account presents a comparative study, emphasizing the impact of engineering nanostructures and selecting magnetic ions in shaping carrier-magnetic ion interactions. Various host materials, including the II-VI group, halide perovskites, and I-III-VI2 in diverse structural configurations such as core/shell quantum dots, seeded nanorods, and nanoplatelets, incorporated with magnetic ions such as Mn2+, Ni2+, and Cu1+/2+ are highlighted. These materials have recently been investigated by us using state-of-the-art steady-state and transient optically detected magnetic resonance (ODMR) spectroscopy to explore individual spin-dynamics between the photogenerated carriers and magnetic ions and their dependence on morphology, location, crystal composition, and type of the magnetic ion. The information extracted from the analyses of the ODMR spectra in those studies exposes fundamental physical parameters, such as g-factors, exchange coupling constants, and hyperfine interactions, together providing insights into the nature of the carrier (electron, hole, dopant), its local surroundings (isotropic/anisotropic), and spin dynamics. The findings illuminate the importance of ODMR spectroscopy in advancing our understanding of the role of magnetic ions in semiconductor nanocrystals and offer valuable knowledge for designing magnetic materials intended for various spin-related technologies.

Copper-doped II-VI and copper-based I-III-VI2 colloidal quantum dots (CQDs) have been at the forefront of interest in nanocrystals over the past decade, attributable to their optically activated copper states. However, the related recombination mechanisms are still unclear. The current work elaborates on recombination processes in such materials by following the spin properties of copper-doped CdSe/CdS (Cu@CdSe/CdS) and of CuInS2 and CuInS2/(CdS, ZnS) core/shell CQDs using continuous-wave and time-resolved optically detected magnetic resonance (ODMR) spectroscopy. The Cu@CdSe/CdS ODMR showed two distinct resonances with different g factors and spin relaxation times. The best fit by a spin Hamiltonian simulation suggests that emission comes from recombination of a delocalized electron at the conduction band edge with a hole trapped in a Cu2+ site with a weak exchange coupling between the two spins. The ODMR spectra of CuInS2 CQDs (with and without shells) differ significantly from those of the copper-doped II-VI CQDs. They are comprised of a primary resonance accompanied by another resonance at half-field, with a strong correlation between the two, indicating the involvement of a triplet exciton and hence stronger electron-hole exchange coupling than in the doped core/shell CQDs. The spin Hamiltonian simulation shows that the hole is again associated with a photogenerated Cu2+ site. The electron resides near this Cu2+ site, and its ODMR spectrum shows contributions from superhyperfine coupling to neighboring indium atoms. These observations are consistent with the occurrence of a self-trapped exciton associated with the copper site. The results presented here support models under debate for over a decade and help define the magneto-optical properties of these important materials.

The quest for atomically precise synthesis of colloidal semiconductor nanostructures has attracted increasing attention in recent years and remains a formidable challenge. Nevertheless, atomically precise clusters of semiconductors, known as magic-size clusters (MSCs), are readily accessible. Ultrathin one-dimensional nanowires and two-dimensional nanoplatelets and nanosheets can also be categorized as magic-size nanocrystals (MSNCs). Further, the magic-size growth regime has been recently extended into the size range of colloidal QDs (up to 3.5 nm). Nevertheless, the underlying reasons for the enhanced stability of magic-size nanostructures and their formation mechanisms remain obscure. In this Perspective, we address these intriguing questions by critically analyzing the currently available knowledge on the formation and stability of both MSCs and MSNCs (0D, 1D, and 2D). We conclude that research on magic-size colloidal nanostructures is still in its infancy, and many fundamental questions remain unanswered. Nonetheless, we identify several correlations between the formation of MSCs and 0D, 1D and 2D MSNSs. From our analysis, it appears that the "magic" originates from the complexity of a dynamic and multivariate system running under reaction control. Under conditions that impose a prohibitively high energy barrier for classical nucleation and growth, the reaction proceeds through a complex and dynamic potential landscape, searching for the pathway with the lowest energy barrier, thereby sequentially forming metastable products as it jumps from one local minimum to the next until it eventually becomes trapped into a minimum that is too deep with respect to the available thermal energy. The intricacies of this complex interplay between several synergistic and antagonistic processes are, however, not yet understood and should be further investigated by carefully designed experiments combining multiple complementary in situ characterization techniques.

The formation mechanisms of colloidal magic-size semiconductor nanostructures have remained obscure. Herein, we report the room temperature synthesis of three species of ultrathin CdTe magic-size nanowires (MSNWs) with diameters of 0.7 ± 0.1 nm, 0.9 ± 0.2 nm, and 1.1 ± 0.2 nm, and lowest energy exciton transitions at 373, 418, and 450 nm, respectively. The MSNWs are obtained from Cd(oleate)2 and TOP-Te, provided diphenylphosphine and a primary alkylamine (RNH2) are present at sufficiently high concentrations, and exhibit sequential, discontinuous growth. The population of each MSNW species is entirely determined by the RNH2 concentration [RNH2] so that single species are only obtained at specific concentrations, while mixtures are obtained at concentrations intermediate between the specific ones. Moreover, the MSNWs remain responsive to [RNH2], interconverting from thinner to thicker upon [RNH2] decrease and from thicker to thinner upon [RNH2] increase. Our results allow us to propose a mechanism for the formation and interconversion of CdTe MSNWs and demonstrate that primary alkylamines play crucial roles in all four elementary kinetic steps (viz., monomer formation, nucleation, growth in length, and interconversion between species), thus being the decisive element in the creation of a reaction pathway that leads exclusively to CdTe MSNWs. The insights provided by our work thus contribute toward unravelling the mechanisms behind the formation of shape-controlled and atomically precise magic-size semiconductor nanostructures.

Impurity doping of low-dimensional semiconductors is an interesting route towards achieving control over carrier dynamics and energetics, e.g., to improve hot carrier extraction, or to obtain strongly Stokes shifted luminescence. Such studies remain, however, underexplored for the emerging family of III-V colloidal quantum dots (QDs). Here, we show through a detailed global analysis of multiresonant pump-probe spectroscopy that electron cooling in copper-doped InP quantum dot (QDs) proceeds on subpicosecond time scales. Conversely, hole localization on Cu dopants is remarkably slow (1.8 ps), yet still leads to very efficient subgap emission. Due to this slow hole localization, common Auger assisted pathways in electron cooling cannot be blocked by Cu doping III-V systems, in contrast with the case of II-VI QDs. Finally, we argue that the structural relaxation around the Cu dopants, estimated to impart a reorganization energy of 220 meV, most likely proceeds simultaneously with the localization itself leading to efficient luminescence.

The growth of two-dimensional platelets of the CdX family (X = S, Se, or Te) in an organic solvent requires the presence of both long- and short-chain ligands. This results in nanoplatelets of atomically precise thickness and long-chain ligand-stabilized Cd top and bottom surfaces. The platelets show a bright and spectrally pure luminescence. Despite the enormous interest in CdX platelets for optoelectronics, the growth mechanism is not fully understood. Riedinger et al. studied the reaction without a solvent and showed the favorable role for short-chain carboxylates for growth in two dimensions. Their model, based on the total energy of island nucleation, shows favored side facet growth versus growth on the top and bottom surfaces. However, several aspects of the synthesis under realistic conditions are not yet understood: Why are both short- and long-chain ligands required to obtain platelets? Why does the synthesis result in both isotropic nanocrystals and platelets? At which stage of the reaction is there bifurcation between isotropic and 2D growth? Here, we report an in situ study of the CdSe nanoplatelet reaction under practical synthesis conditions. We show that without short-chain ligands, both isotropic and mini-nanoplatelets form in the early stage of the process. However, most remaining precursors are consumed in isotropic growth. Addition of acetate induces a dramatic shift toward nearly exclusive 2D growth of already existing mini-nanoplatelets. Hence, although myristate stabilizes mini-nanoplatelets, mature nanoplatelets only grow by a subtle interplay between myristate and acetate, the latter catalyzes fast lateral growth of the side facets of the mini-nanoplatelets.