Perovskite has been proven a promising class of materials for optoelectronic applications. In particular, due to its remarkable optical properties, such as high optical absorption coefficient, emission yield, and dielectric constants, perovskite has emerged as a potential candidate for active gain materials. Perovskite micro/nano lasers exhibit lower thresholds, better spectral coherence and wider emission gamut than conventional lasers.
Although there are a great number of researches on small laser, the optical gain coefficient of perovskite micro/nano-structureshas never been reported, which directly influences the performance of laser. To explore their applications and further improve performance, it is essential to understand the opitcal gain and the anistropic properties.
Up to the present, almost all the methods of characterizing optical gain coefficient are based on large-area thin films or liquid using macroscopic free light paths, which can not distinguish the micro/nanostructures so as to study optical gain properties of micro/nanostructures. Thus, microscale measuring methods that can provide sufficient spatial resolution for perovskite micro/nanostructures are necessary to see more beyond the average effect.
Recently, a research team led by Prof. LIU Xinfeng from the National Center for Nanoscience and Technology (NCNST) of the Chinese Academy of Sciences (CAS), reported all optical switching through anistropic gain of CsPbBr3 single crystal microplatelet (MP) with orthorhombic phase. The research is published on NanoLetters.
In this work, they obtained high quality CsPbBr3 MPs with anisotropic orthorhombic phase. Optical gain of CsPbBr3 single crystal MP was investigated via micro-scale variable stripe-length measurement. A polarization-dependent optical gain was observed and the gain along  is larger than that of [1-10]. The behavior was attributed to the lowest energy transition dipole moment of  induced by the smaller deviation of Br-Pb-Br bond from the perfect lattice. Along the  direction, we obtained the optical gain value up to 5077 cm-1, which is the record value ever reported. Using exciton model and free carrier model, they confirmed carriers exist in the form of excitons and the excitons recombine radiatively to produce photons under lower carrier density. With the carrier density increasing more than Mott density, excitons start to separate into free carriers and additional nonradiative processes may come into play in determining the optical losses.
Moreover, all optical switching of lasing are realized by periodical polarized excitation based on the anistropic optical gain. This study provide new perceptions in the design of novel functional anistropic devices based on perovskite micro/nanostructures.
Figure 1. The CsPbBr3 single crystal microplatelet with anisotropic orthorhombic phase. (Image by LIU Xinfeng et al)
Figure 2. (a) Schematic of microscopic optical setup. (b) The anisotropic optical gain and (c) pump-fluence-dependent optical gain behaviors of CsPbBr3 MPs along [00-2] direction. (Image by LIU Xinfeng et al)
Figure 3. Optical switching between lasing on and lasing off by the polarization. (Image by LIU Xinfeng et al)
National Center for Nanoscience and Technology