Effect of ion migration on lead halide perovskite on visible light communication system.

Benefiting from the high modulation bandwidth (BW), low energy consumption and excellent optical performance, lead halide perovskite has attracted wide attention in visible light communication (VLC). However, the ion migration which results in mobile point defects in perovskite structures is recognized as a crucial key factor inducing the performance degradation. Here, the influence of ion migration in perovskite devices on the performance of VLC was systematically studied. The ion migration process is realized by mixing CsPbBr3 and CsPbI3 quantum dots, during which, the performance of the VLC system is reduced, but it can return to its initial state after stabilization. The on-off keying (OOK) modulation scheme of the perovskite light-emitting diode (LED) device was carried out, achieving a data rate of 90 Mbps.

Stable and Ultrafast Blue Cavity-Enhanced Superfluorescence in Mixed Halide Perovskites.

Cavity-enhanced superfluorescence (CESF) in quantum dot (QD) system is an ultrafast and intense lasing generated by combination of quantum coupling effect and optically stimulated amplification effect, which can provide a new idea for realizing high quality blue light sources and address the limitation of conventional inefficient blue light sources. Modifying halide composition is a straightforward method to achieve blue emission in perovskite QD system. However, the spectral instability introduced by photoinduced halide phase segregation and low coupling efficiency between QDs and optical cavities make it challenging to achieve stable blue CESF in such halide-doped QD system. Herein, long-range-ordered, densely packed CsPbBr2 Cl QD-assembled superlattice microcavities in which the two core issues can be appropriately addressed are developed. The QD superlattice structure facilitates excitonic delocalization to decrease exciton-phonon coupling, thus alleviating photoinduced phase segregation. By combination of theoretical analysis and temperature-dependent photoluminescence (PL) measurements, the underlying photoinduced phase segregation mitigation mechanism in mixed halide superlattices is clarified. Based on the CsPbBr2 Cl QD superlattices with regularly geometrical structures, in which the gain medium can be strongly coupled to the naturally formed microcavity, stable and ultrafast (3 ps) blue CESF with excellent optical performance (threshold ≈33 µJ cm-2 , quality factor ≈1900) is realized.

Highly Efficient and Stable CdZnSeS/ZnSeS Quantum Dots for Application in White Light-Emitting Diode.

Semiconductor quantum dots (QDs) are a promising luminescent phosphor for next-generation lightings and displays. In particular, QD-based white light-emitting diodes (WLEDs) are considered to be the candidate light sources with the most potential for application in displays. In this work, we synthesized quaternary/ternary core/shell alloyed CdZnSeS/ZnSeS QDs with high bright emission intensity. The QDs show good thermal stability by performing high temperature-dependent experiments that range from 295 to 433 K. Finally, the WLED based on the CdZnSeS/ZnSeS QDs exhibits a luminous efficiency (LE) of 28.14 lm/W, an external quantum efficiency (EQE) of 14.86%, and a warm bright sunlight close to the spectrum of daylight (Commission Internationale de l'éclairage (CIE) coordinates 0.305, 0.371). Moreover, the photoluminescence (PL) intensity, LE, EQE, and correlated color temperature (CCT) of as-prepared QD WLED remained relatively stable with only slight changes in the luminescence stability experiment.

Ultrastable low-cost colloidal quantum dot microlasers of operative temperature up to 450 K.

Quantum dot microlasers, as multifunctional optical source components, are of great importance for full-color high-pixel display, miniaturized coherent lighting, and on-chip integrated photonic and electronic circuits. Since the first synthesis of colloidal quantum dots (CQD) in the 1990s, motivation to realize high-performance low-cost CQD micro-/nanolasers has been a driving force for more than three decades. However, the low packing density, inefficient coupling of CQDs with optical cavities, and the poor thermal stability of miniaturized complex systems make it challenging to achieve practical CQD micro-/nanolasers, especially to combine the continuous working ability at high temperatures and the low-cost potential with mass-produced synthesis technologies. Herein, we developed close-packed CQD-assembled microspheres and embedded them in a silica matrix through the rapid self-aggregation and solidification of CdSe/ZnS CQD. This technology addresses the core issues of photoluminescence (PL) quenching effect and low optical gain in traditional CQD laser research. High-efficiency low-threshold CQD microlasers are demonstrated together with long-playing (40 min) working stability even at 450 K under pulsed laser excitation, which is the highest operational temperature for CQD lasers. Moreover, single-mode CQD microlasers are obtained with tunable wavelengths across the entire visible spectral range. The chemosynthesis process supports the mass-produced potential of high-density integrated CQD microlasers, promoting CQD-based low-cost high-temperature microdevices.

Linearly polarized lasing based on coupled perovskite microspheres.

The polarization of lasing, as a fundamental property related to the emission coherence of microlasers, is one of the criteria for a high quality laser beam but has been rarely investigated. Unlike conventional lasers which can be induced by highly polarized seed light or by using a polarizing film, the microlaser for on-chip integrated photonic circuits generally possesses a low degree of polarization due to unpolarized spontaneous emission. Here, we firstly demonstrate that the Vernier effect can be used to improve the degree of polarization from ∼0.2 to 0.78 based on metal halide perovskite microspheres. After coupling, linearly polarized single-mode lasing with a low threshold and high quality can be achieved. In addition, by using the finite element method, the mode distributions of CsPbBr3 microspheres before and after coupling are analyzed systematically and a clear physical diagram of coupled resonances is obtained. Our work clearly suggests that a coupled linearly polarized single-mode microlaser by the Vernier effect would offer a real step closer to the platform for on-chip integrated photonics.

Cooperative excitonic quantum ensemble in perovskite-assembly superlattice microcavities.

Perovskites-compounds with the CaTiO3-type crystal structure-show outstanding performance in photovoltaics and multiparameter optical emitters due to their large oscillator strength, strong solar absorption, and excellent charge-transport properties. However, the ability to realize and control many-body quantum states in perovskites, which would extend their application from classical optoelectronic materials to ultrafast quantum operation, remains an open research topic. Here, we generate a cooperative quantum state of excitons in a quantum dot ensemble based on a lead halide perovskite, and we control the ultrafast radiation of excitonic quantum ensembles by introducing optical microcavites. The stimulated radiation of excitonic quantum ensemble in a superlattice microcavity is demonstrated to not be limited by the classical population-inversion condition, leading to a picosecond radiative duration time to dissipate all of the in-phase dipoles. Such a perovskite-assembly superlattice microcavity with a tunable radiation rate promises potential applications in ultrafast, photoelectric-compatible quantum processors.