Perovskite nanocrystals (NCs) of a fully inorganic composition have emerged as effective materials for optoelectronic applications over the past decade. Their photoluminescence and stability are significantly influenced by the surface chemistry, particularly the surfactant molecules used for defect passivation. While several experiments have investigated the ligand dependence of the spontaneous emission properties, the ligand's role in the optical gain and stimulated emission for perovskite NCs has almost entirely been unexplored.

In this work, we aim to fill this gap, investigating how the capping ligand of CsPbBr3 perovskite NC thin films affects their amplified spontaneous emission (ASE) characteristics, their photostability, and their sensitivity to ambient air.

We analyzed four distinct samples with different capping ligands, namely oleic acid/oleylamine, didodecyldimethylammonium bromide, 3-(N,N-dimethyloctadecylammonio)-propanesulfonate, and lecithin. We discuss the impact of these four ligands on the NCs' quantum efficiency, optical gain, optical stability, and atmospheric sensing properties, investigating the underlying chemical–physical mechanisms responsible for the observed variations. In particular, we show that all of the samples show ASEs under nanosecond pumping, but with very different thresholds, and that the dependence of the ASE's intensity on the sample environment is also strongly ligand-dependent.
Finally, we performed a comparison between these four ligands, demonstrating that lecithin capping allows the optimal performance to be obtained concerning the ASE threshold and sensing capabilities.