Direct Band Gap Chalcohalide Semiconductors: Quaternary AgBiSCl2 Nanocrystals

Heavy pnictogen chalcohalide semiconductors are coming under the spotlight for energy conversion applications. Here we present the colloidal synthesis of phase pure AgBiSCl2 nanocrystals. This quaternary chalcohalide compound features a quasi-two-dimensional crystal structure and a direct band gap, in contrast with the monodimensional structure and the indirect band gap peculiar to the orthorhombic, ternary Bi chalcohalides. Consistently, colloidal AgBiSCl2 nanocrystals exhibit photoinduced luminescence compatible with both band edge excitons and midgap states. This is the first observation of band edge emission in chalcohalide nanomaterials at large, although exciton recombination in our AgBiSCl2 nanocrystals mostly occurs via nonradiative pathways. This work further advances our knowledge on this class of mixed anion semiconductor nanomaterials and provides a contribution to establishing chalcohalides as a reliable alternative to metal chalcogenides and halides.