Involvement of Sub-Bandgap States in Subpicosecond Exciton and Biexciton Dynamics of Ternary AgInS2 Nanocrystals.

Abstract

We have synthesized three AgxInS2 (AIS) ternary nanocrystals (NCs), where x varies from 0.25 to 1, and reported their biexcitonic feature which depends on the stoichiometry ratio of Ag/In. The broadening of absorption band and dual photoluminescence in different AIS NCs indicates the existence of Ag-related sub-bandgap (S-states) and antisite states. Ultrafast charge carrier dynamics in AIS NCs that involve multiple states like higher excited state, band-edge, Ag-related sub-bandgap, and antisite states have been carried out by employing femtosecond transient absorption spectroscopy, which strongly depends on Ag/In ratio. The probe-induced biexcitonic feature that originated from antisite state has been observed in these AIS NCs even at low pump fluency (<N> = ∼0.2). The enhancement of binding energy of biexciton and slow down of electron cooling dynamics has been demonstrated by gradual increment of pump fluence as well as with different stoichiometry of Ag and In.