Over the last decade, fully inorganic lead halide perovskite nanocrystals (NCs) have received a lot of attention as active materials for photonic and optoelectronic devices. Despite their high sensitivity to ambient conditions typically inducing irreversible degradation mechanisms, some experiments have evidenced reversible environmental effects, clearing the way for their application as active materials for resistive and optical sensors. In particular, the sensitivity of CsPbBr 3 NC thin films to ambient air was demonstrated, noticeable as reversible modulation of the PL and ASE intensities, which is a sign of physical perovskite–air interactions, ruling out degradation effects. The air's humidity determines the solvation of the surface and the hydrophilic ligand's head group, resulting in the formation of surface trap states that modulate the emitted PL intensity; in a vacuum, water molecules can be desorbed, restoring pristine …