Naoto Shirahata

Diamond-cubic silicon is a promising quantum-dot material for sustainable optoelectronics owing to its abundance, nontoxicity, and size-tunable photoluminescence (PL). However, silicon quantum-dot light-emitting diodes (Si-QLEDs) suffer from severe efficiency roll-off at high current densities, and the underlying electroluminescence (EL) dynamics remain poorly understood. Here, transient EL measurements using time-correlated single-photon counting reveal that the EL lifetime of Si-QLEDs remains nearly constant at ∼13 μs under varied off-bias conditions and is approximately 8.7 times shorter than the corresponding PL lifetime (∼114 μs). In contrast, CdSe/ZnS QLEDs exhibit the conventional relationship in which the EL lifetime exceeds the PL lifetime. This anomalous EL–PL lifetime inversion in Si-QLEDs is accompanied by a pronounced EQE roll-off at high current densities. Time-resolved current analysis reveals a slow relaxation component possibly associated with trap-related carrier dynamics, while the EL peak energy shows a stronger dependence on current density than on applied voltage. Carrier imbalance and Auger recombination remain possible nonradiative mechanisms under electrical excitation, although their individual contributions to the shortened EL lifetime and efficiency roll-off cannot be independently quantified from the present measurements. In addition, increasing reverse off-bias markedly prolongs the EL delay time, indicating that charge accumulation and trap filling primarily govern the carrier-preparation stage preceding radiative recombination. These findings reveal distinct carrier dynamics in Si-QLEDs and highlight charge-balance control and trap-state reduction as important strategies for mitigating efficiency roll-off.

We report here a new precursor‐based approach for synthesizing colloidal indium antimonide quantum dots (InSb QDs) that emit light in the short‐wavelength infrared (SWIR) region. The synthesis was carried out using indium and antimony carboxylates. Antimony(III) acetate was converted into Sb(PA) ₃ and Sb(LA) ₃ (PA = palmitic acid, LA = lauric acid) to improve their solubility and stability in octadecene (ODE). The synthesis employed air‐stable tris(dimethylamino)phosphine as the reducing agent, enabling a safer and milder reaction. X‐ray powder diffraction confirmed the formation of single‐phase InSb without any impurity phases. By controlling the ligand chain length and the purification conditions, we obtained size‐tunable photoluminescence (PL) spectra with peak wavelengths ranging from 870 to 1510 nm. Shorter alkyl ligands and the addition of trioctylphosphine facilitated the growth of larger particles, leading to a redshift in the PL spectra. This study demonstrates that precursor and ligand design can effectively control the particle size and optical properties of InSb QDs, providing a versatile synthetic route for developing III–V semiconductor QDs with tunable emission across a broad SWIR wavelength range.

Tin iodide perovskite nanocrystals are compelling lead-free candidates for solution-processed optoelectronics, yet their reported photoluminescence (PL) signatures are marked by persistent and unresolved anomalies. Literature reports show that PL energies can vary widely among nanocrystals of comparable size and that charge carriers can exhibit decoupling between the PL quantum yield and PL lifetime, along with slow hot-carrier relaxation dynamics. Low-temperature studies introduce further complexity, including the emergence of additional emissive features and nonmonotonic spectral evolution. In this Perspective, we consolidate these seemingly disparate observations into a unified framework and critically assess the key factors that complicate the interpretation of tin iodide nanocrystal photophysics. These include polymorphous or locally distorted crystal structures, structural defects coupled with hole doping, and trace two-dimensional Ruddlesden-Popper phases that can dominate the observed PL while evading routine structural characterization. Finally, we outline actionable research directions, such as the phase-pure synthesis of highly luminescent nanocrystals through rational ligand and precursor control or doping engineering, defect-tolerant surface design, and stringent structure-spectroscopy correlations, to transform apparent "anomalies" into testable physical mechanisms and establish robust structure-photophysics relationships for tin halide perovskite nanocrystals.

A one-pot synthesis of InSb/InP core–shell quantum dots (QDs) was developed, enabling the first observation of electroluminescence from LEDs with these QDs as the active layer.

Lead-free chalcogenide perovskites are emerging as promising alternatives to hybrid halide perovskites due to their superior thermal stability, non-toxicity, and strong optical absorption. In this study, the photovoltaic performance of single-junction BaHfSe₃-based perovskite solar cells (PSCs) with the TCO/TiO₂/BaHfSe₃/Cu₂O/Au configuration is systematically investigated using SCAPS-1D simulations. Device optimization identifies TiO₂ and Cu₂O as suitable ETL and HTL materials, respectively. The optimized structure—TCO/TiO₂ (50 nm)/BaHfSe₃ (500 nm)/Cu₂O (100 nm)/Au—achieves a power conversion efficiency (PCE) of 24.47% under standard conditions. Simulation results reveal that device efficiency is influenced by absorber thickness and trap density. A detailed temperature-dependent study highlights that photovoltaic parameter efficiency is governed by the barrier alignment at the TCO/ETL interface. For lower TCO (Transparent Conducting Oxide) work functions (3.97–4.07 eV), PCE decreases monotonically with temperature, attributed to the increase in reverse saturation current resulting from a higher intrinsic carrier concentration. By contrast, higher TCO work functions (4.47–4.8 eV) yield an initial increase in efficiency with temperature, driven by reduced barrier height and favorable Fermi level shifts before efficiency declines at further elevated temperatures. These insights underscore the promise of BaHfSe₃ as a lead-free, environmentally robust perovskite absorber for next-generation PSCs, and highlight the critical importance of interface engineering for achieving optimal thermal and operational performance.

III–V semiconductor quantum dots (QDs) are RoHS-compliant materials that feature tunable bandgaps and strong quantum confinement. However, the synthesis of InP₁₋ₓSbₓ QDs (0 ≤ x ≤ 1) has been limited by the reliance on hazardous hydride reductants and restricted precursor chemistry. Here, we report a metal-reductant-free strategy using tris(dimethylamino)phosphine [P(NMe2)3] as both phosphorus source and mild reductant, representing the first such approach for InP₁₋ₓSbₓ QDs. The coordination environment of antimony is found to dictate the product composition: Sb–oleylamine complexes afford phase-pure InSb QDs, whereas Sb–trioctylphosphine (TOP) complexes facilitate the formation of alloyed InP₁₋ₓSbₓ QDs (0 ≤ x < 1). The resulting QDs exhibit sharp excitonic absorption features and band-edge emission in the short-wavelength infrared region. Alloying enables continuous bandgap tuning, thereby bridging the previously unobserved emission gap between InP and InSb QDs. This work establishes a safe, high-yielding, and versatile synthetic route to Sb-based III–V QDs and provides a general design principle for expanding the compositional diversity of colloidal semiconductors.

We report on the impact of impurity doping on performance enhancement of silicon quantum dot (SiQD) light-emitting diodes.

We report for the first time the amplified spontaneous emission (ASE) and lasing from blue-emitting silicon nanoclusters. The lasing threshold is determined as 1.8 mJ per pulse and the emission peaks at 434 nm.