Amplified Spontaneous Emission in Thin Films of CsPbX3 Perovskite Nanocrystals

摘要

During the last years, Metal Halide Perovskites (MHPs) have attracted special attention as an efficient conversion films for photovoltaics, or excellent gain media to construct optical sources. In spite of the fact that most of the works have been focussed on CH3NH3PbX3 (X=Cl, Br, I) polycrystalline thin films, MHP can be also synthesized as colloidal nanocrystals. In particular, caesium lead halide perovskite CsPbX3 nanocrystals (NCs) revealed extraordinary properties for optoelectronics. With a high quantum yield of emission (>90%) at room temperature and linewidths less than 100 meV, CsPbX3 NCs have demonstrated favourable characteristics for active photonics. Indeed, thin films of CsPbBr3 optically pumped by femtosecond pulses resulted in amplified spontaneous emission (ASE) with thresholds less than 10 μJ/cm² or lasers with linewidths narrower than 0.2 nm. A further improvement of these results towards the performances demonstrated by their counterpart polycrystalline films, however, requires a reduction of different nonradiative recombination channels restricting the ASE. In this work, films of CsPbBr3 NCs are properly optimized to enhance the generation of photoluminescence (PL), and with it the optical gain. Indeed, the dependence of PL on temperature reveals the activation energies of nonradiative traps higher than 10 meV. Consequently, these films demonstrate ASE thresholds less than 5 μJ/cm² at cryogenic temperatures under nanosecond excitation. These preliminary results pave the road towards a CsPbBr3 active photonics technology.