Quantum Optoelectronics

Abstract:

The optical Aharonov-Bohm effect in a quantum ring was investigated in terms of magnetic field dependence of excitons and biexcitons. The fine exciton states of quantized orbital angular momentum in a quantum ring were considered theoretically, and the presence of quantum beats was predicted as evidence of the quantum coherence of the fine exciton states. In the case of GaAs/GaAlAs quantum rings grown by the droplet epitaxy, we found various disorder effects are associated such as structure anisotropy, localization, and internal electric field, resulting in a modulation of the oscillation periods. Additionally, we found that a strongly correlated exciton pair can be formed in a single quantum ring similar to the Wigner molecule. In this case, the biexciton emission energy changes abruptly at transition magnetic fields with a fractional oscillation period compared to that of the exciton, the so-called fractional optical Aharonov-Bohm oscillations.

Abstract:

The optical properties of graphene (Gr)-covered CsPbBr₃ quantum dots (QDs) were investigated using micro-photoluminescence spectroscopy, revealing a remarkable three orders of magnitude enhancement in photoluminescence (PL) intensity compared to bare CsPbBr₃ QDs. To elucidate the underlying mechanisms, we combined experimental techniques with density functional theory (DFT) calculations. DFT simulations showed that the graphene layer generates interfacial electrostatic potential barriers when in contact with the CsPbBr₃ surface, impeding carrier leakage from perovskite to graphene and enhancing radiative recombination. Additionally, graphene passivates CsPbBr₃ surface defect states, suppressing nonradiative recombination of photo-generated carriers. Our study also revealed that graphene becomes n-doped upon contact with CsPbBr₃ QDs, activating its plasmon mode. This mode resonantly couples with photo-generated excitons in the perovskite. The momentum mismatch between graphene plasmons and free-space photons is resolved through plasmon scattering at Gr/CsPbBr₃ interface corrugations, facilitating the observed super-bright emission. These findings highlight the critical role of graphene as a top contact in dramatically enhancing CsPbBr₃ QDs’ PL. Our work advances the understanding of graphene-perovskite interfaces and opens new avenues for designing high-efficiency optoelectronic devices. The multifaceted enhancement mechanisms uncovered provide valuable insights for future research in nanophotonics and materials science, potentially leading to breakthroughs in light-emitting technologies.

Abstract:

The development of inexpensive and easily processable X-ray-sensitive materials is of great importance because a number of commercial scintillators, such as LaBr3(Ce), Gd3Al3Ga2O12(Ce), Cs2HfCl6, NaI:Tl, CsI:Tl, and LiI:Eu, are fabricated using highly toxic or rare-earth elements via high-temperature synthesis. This has spurred research into radioluminescence-enhancing mechanisms and solution-processable scintillating materials made from earth-abundant elements that have excellent optoelectronic properties, including high quantum yields and a low afterglow effect. In recent years, a range of metal halide perovskite (MHP) integrated with thermally activated delayed fluorescence (TADF) materials have been developed, exhibiting excellent scintillation properties and a high spatial resolution. Meanwhile, plasmonic technologies are reported to exploit light-energy confinement capabilities beyond the diffraction limit that produces local-field enhancement. This enhancement has subsequently improved the performance of small-sized optoelectronic devices such as solar cells and diagnostic optical sensors. This perspective summarizes the current development of innovative MHP, TADF, and plasmonic materials for use in scintillators and their integrated moieties while also identifying the relevant challenges. Following a thorough evaluation of the efforts made to improve the X-ray scintillation efficiency of these materials, we propose an outlook for future research in order to further enhance their scintillation properties and spatial resolution.

Abstract:

Mixed halide perovskites exhibit promising optoelectronic properties for next-generation light-emitting diodes due to their tunable emission wavelength that covers the entire visible light spectrum. However, these materials suffer from severe phase segregation under continuous illumination, making long-term stability for pure red emission a significant challenge. In this study, we present a comprehensive analysis of the role of halide oxidation in unbalanced ion migration (I/Br) within CsPbI2Br nanocrystals and thin films. We also introduce a new approach using cyclic olefin copolymer (COC) to encapsulate CsPbI2Br perovskite nanocrystals (PNCs), effectively suppressing ion migration by increasing the corresponding activation energy. Compared with that of unencapsulated samples, we observe a substantial reduction in phase separation under intense illumination in PNCs with a COC coating. Our findings show that COC enhances phase stability by passivating uncoordinated surface defects (Pb2+ and I–), increasing the formation energy of halide vacancies, improving the charge carrier lifetime, and reducing the nonradiative recombination density.