Quantum Optoelectronics

Abstract:

The accelerating growth of the hydrogen (H2) economy is pivotal for achieving large-scale decarbonization of current energy resources. Ensuring safe and efficient handling of this potentially hazardous resource has led to an increasing demand for fast, selective and reliable H2 sensors. In this work, we report a nanohybrid H2 sensing platform comprising uniformly dispersed AuPd bimetallic nanoparticles (BNPs) embedded in a ZnO-based metal oxide semiconductor (MOS) matrix infiltrated within an anodized porous silicon (PSi) framework. This hybrid design (PSi-MOS#AuPd) synergistically merges the strong chemisorption affinity and rapid desorption kinetics of Pd with the enhanced catalytic activity and electronic modulation imparted by AuPd interactions. Precise control over BNPs thickness (~ 8.6 nm) ensures uniform dispersion and effectively mitigates the inherent volume expansion of Pd during hydrogenation, maintaining structural integrity and catalytic efficiency. The PSi support characterized by high porosity (~1.1 μm) and superhydrophobicity (θ w  = 153.6° ± 0.2°), promotes efficient gas diffusion and enhances humidity resilience. The resulting sensor exhibits remarkable performance, including high sensitivity ~46 %@50ppm, low-operating temperature (~90 °C), rapid response time (~14 s), excellent stability over 60 days and strong selectivity against interfering gases (H2S, NH3, NO2, and CO) under varying humidity conditions (25–85 % RH). This work paves the way for the advancement of H2 sensors and highlights the potential of substrate engineering and bimetallic synergy in enhancing gas sensing technology for safety-critical applications.

Abstract:

Abstract Advancements in utilizing low refractive index dielectric particles have implications for sensing, lasing, and strong‐coupling at nano and microscopic scales. These cavities offer benefits like ease of fabrication and biocompatibility, making them promising for a wide range of technologies by utilizing their narrow linewidth modes. However, optical modes sustained in these dispersive systems can show distinct behaviors depending on the detection configuration. This study shows the influence of numerical aperture (NA) of the objective lens on the detection of Mie modes in a dielectric microsphere under far‐field excitation and collection. It is demonstrated experimentally and numerically that Mie modes from microspheres outcouple at different angles, with variations in mode amplitudes contingent on the NA of the objective lens, thus leading to distinct linewidths while probing with different NA objectives. Furthermore, it is shown that metallic substrates can facilitate efficient detection of Mie modes by redirecting scattered modes towards low angles. This enables mode detection with low NA lenses and further preventing the inclusion of incident scattered light from higher angles which otherwise perturb the modes. The results underline the importance of careful detection strategies to fully harness dielectric particles as optical platforms for applications in particle detection and characterization.

Abstract:

Two-dimensional layered perovskite oxides have emerged as promising photocatalysts for solar-driven hydrogen evolution. Although doping has been widely employed to enhance photocatalytic performance, its role in modulating the electronic structure and the local chemical environment of these materials remains poorly understood. Here in this study, we investigate the codoping of Rh and La into exfoliated nanosheets of the Dion–Jacobson perovskite KCa2Nb3O10 to enhance photocatalytic hydrogen evolution reaction (HER) activity. A substantial increase in H2 evolution rate, from 12.3 to 69.0 μmol h–1, was achieved at an optimal doping level of 0.2 wt % Rh and 1.3 wt % La. Comprehensive structural and spectroscopic analyses, including synchrotron techniques and high-resolution microscopy, revealed that Rh3+ substitutes Nb5+ to introduce shallow 4d acceptor states that mediate charge separation, while La3+ substitutes Ca2+, compensates for aliovalent charge imbalance, and modulates local lattice distortions and oxygen vacancy formation. This codoping strategy enhances charge carrier lifetime and separation efficiency through a trap-mediated mechanism. The observed volcano-shaped activity trend highlights a narrow compositional window, where electronic and structural factors are optimally balanced. These findings establish a mechanistic foundation for defect engineering in layered perovskites and offer a pathway for the rational design of photocatalysts.

Abstract:

Room‐temperature collective quantum emission (RT‐CQE), enabled by many‐body interactions and phase‐synchronized dipole oscillations, offers a promising path for scalable quantum photonics. Here, superfluorescence (SF) is demonstrated in CsPbBr3 perovskite nanowires (NWs), facilitated by Wannier–Mott excitons with spatially delocalized wavefunctions and strong dipole–dipole interactions. The intrinsic quasi‐1D geometry and occasional bundling promote preferential dipole alignment along the NW axis, enabling long‐range phase coherence. Key experimental signatures, photon bunching with g2(0) ≈2, femtosecond‐scale coherence time (≈88 fs), and ultralow excitation threshold (≈210 nJ−1 cm2), confirm the onset of SF at ambient conditions. Ultrafast spectroscopy reveals bandgap renormalization, state filling, and exciton‐phonon coupling, consistent with collective excitonic behavior mediated by delocalized states. Unlike other RT‐SF mechanisms based on polarons or electron–hole liquids, the system exploits directional dipole alignment and exciton delocalization in quasi‐1D NWs, allowing coherent emission without the need for high excitation densities or complex structural ordering. These findings demonstrate that CsPbBr3 NWs can sustain RT‐SF driven by exciton delocalization and directional dipole coupling, providing a new physical platform for coherent light generation under ambient conditions.

Abstract:

Lead halide perovskite nanocrystals exhibit excellent optoelectronic properties, yet simultaneous observation of bright singlet and triplet exciton emissions under identical conditions has remained elusive. This limitation hinders optimization of quantum efficiency in light-emitting devices. Here, we provide the direct spectroscopic evidence for coexisting bright singlet and triplet excitons in CsPbBr3 nanocrystals, overcoming the conventional 25 % spin-statistical efficiency ceiling. Using polarization-resolved, spatially resolved, and time-resolved micro-photoluminescence at 7 K, we resolve three sharp triplet fine-structure components (T1, T2, T3) with energy separations of 1–3 meV and linear polarization >85 %, coexisting with broad singlet emission. The triplet emissions display distinct polarization axes, nonlinear intensity scaling, and nanosecond lifetimes, confirming their assignment as Rashba-split bright triplet states. Spatial mapping reveals that these emissions arise from structurally pristine domains with exciton diffusion lengths exceeding 9 μm. Time-resolved measurements show concurrent fast and slow decay components, consistent with singlet-to-triplet intersystem crossing followed by radiative triplet recombination. Our findings establish a comprehensive picture of exciton spin dynamics in perovskite nanocrystals and open new avenues for spin-engineered photonic devices. This work lays the foundation for next-generation LEDs, lasers, and quantum light sources that leverage both singlet and triplet radiative channels to exceed traditional efficiency limits. While these findings are demonstrated at cryogenic temperatures, they highlight essential spin-related mechanisms that could be harnessed for room-temperature operation through enhanced Rashba coupling, dielectric engineering, or compositional tuning.