Air sensitive Amplified Spontaneous Emission in lecithin capped CsPbBr3 nanocrystals thin films

Fully inorganic lead halide perovskite nanocrystals (NCs) are receiving great attention as active materials for photonic and optoelectronic devices. While the lack of long-term stability, due to their sensitivity to ambient air exposure, currently prevents their application to commercial devices, the presence of reversible environmental effects opens the way for possible applications of lead halide perovskites in resistive or optical sensors. In this work we investigate the Amplified Spontaneous Emission (ASE) properties and their dependence on the surrounding environment of lecithin-capped CsPbBr3 NCs thin films. We demonstrate low ASE threshold under nanosecond pumping, both in air and in vacuum, with emission intensity lower in air than in vacuum. We also show that the emission quenching induced by ambient air exposure, ascribed to moisture-induced surface solvation, is reversible and it is fully restored by a suited vacuum stint application. The ASE sensitivity is up to 6.5 larger than the spontaneous emission one, making lecithin-capped CsPbBr3 NCs thin films promising systems for the development of optical humidity sensors with high sensitivity.