Cesium lead halide perovskites emitting blue light in the 460−470 nm range of wavelengths have so far been plagued with rather poor luminescent performance, placing inevitable limitations on the development of perovskite nanocrystal-based blue light-emitting devices. Herein, a selective surface defect elimination process with the help of hydrated nitrates was introduced into the perovskite/toluene solution to strip the undesired surface defects and vacancies and to boost the photoluminescence quantum yield of true-blue-light-emitting (at 466 nm) CsPb(Cl/Br) 3 perovskite nanocrystals to the impressive value of 85%. Unlike the conventional passivation strategy, the anionic nitrate ions are able to desorb the undesired surface metallic lead and combine with excess surface metal ions, leaving perovskite quantum dots with better crystallinity and fewer surface defects.

The rapid development of lasers since their launch has given a new lease to traditional optical technology and immensely boosted the development of natural science. Benefiting from the salient light absorption and light emission traits, perovskite lasers show incalculable prospects in applications of optical storage, optical interconnects, high-quality displays, on-chip photonic communications, etc. For perovskite lasers, device structure and working principle rather than just material property are also profound, especially for the realization and assessment of electrically pumped lasers, which is the prerequisite for the ultimate practical application of perovskite lasers. With this in mind, the key characteristic parameters of possible future electrically pumped lasers are discussed herein, and a systematic review of perovskite lasers is presented in a sequential order of development. To begin, the components of lasers are introduced in detail, with an emphasis on optical microcavities and diverse proposed working mechanisms, followed by introductions of representative advances in pulsed optically pumped perovskite lasers with various lasing modes, as well as state-of-the-art developments in lasing phenomenon under continuous-wave optical pumping. Finally, the challenges and fruitful progress toward electrically pumped perovskite lasers are discussed emphatically. It is hoped that this review will promote the realization of perovskite electrically pumped lasers and commercialization of perovskite lasers.

Orthorhombic γ-CsPbI 3 possesses the highest structural stability among the optically active (light-emissive) CsPbI 3 perovskites. Here, we make use of a seed-assisted heteroepitaxial growth to fabricate seed/core/shell CaI x /γ-CsPbI 3 / CaI 2 nanocrystals. Ultrasmall CaI x nanoparticles serve as seeds to template the Pbcentered octahedral arrangement which enables the formation of the γ-CsPbI 3 phase and at the same time inhibit lattice strain by blocking the force transfer that otherwise leads to an octahedral twist and so improve the structural stability of the resulting nanocrystals. An outer shell composed from the same material, CaI 2 , isolates the formed γ-CsPbI 3 nanocrystals from the environment, which also significantly improves their stability under ambient conditions. Optical and electrical studies indicate that the seed/core/shell CaI x /γ-CsPbI 3 /CaI 2 structure possesses a shallower set of trap states as compared to cubic α-CsPbI 3 nanocrystals. Lightemitting diodes utilizing these γ-CsPbI 3 nanocrystals show a record high external quantum efficiency of 25.3%, high brightness of over 13600 cd/m 2 , and an operational lifetime of ∼14 h before reaching 50% of their initial luminance. These devices can repeatedly be illuminated over 650 times at ∼500 cd/m 2 with no decline of brightness, which indicates their great commercial potential.