Optical characterization of the AgInS2 nanocrystals synthesized in aqueous media under stoichiometric conditions

The optical characteristics of AgInS2 nanocrystals (NCs) synthesized in aqueous solutions in the presence of aliphatic mercaptoacids under stoichiometric conditions (at a [Ag]:[In]:[S] molar ratio of 1:1:2) have been studied with micro-Raman, optical absorption, photoluminescence (PL) and PL excitation spectroscopy. The X-ray diffraction (XRD) proved predominant formation of nanocrystals (NCs) of chalcopyrite AgInS2 phase of the average diameter about 4 nm. Micro-Raman spectra confirmed formation of coexisting the chalcopyrite AgInS2 and cubic AgIn5S8 phases. The PL of the undoped and Zn-doped NCs embedded in polymer films of gelatin is found to be caused by defects localized in the NCs of two different ensembles each of which generates its own PL band. It is assumed that one of the ensembles is composed of the NCs of chalcopyrite phase and the other contains NCs of secondary phase, presumably of the cubic AgIn5S8.