Study of the Partial Ag-to-Zn Cation Exchange in AgInS2/ZnS Nanocrystals

AgInS2-ZnS (AIZS) nanocrystals (NCs) were synthesized using a simple one-step approach by heating a Ag/In/Zn/S solution to 210 degrees C providing highly tunable photoluminescence (PL). The incorporation of Zn even at low temperatures (similar to 150 degrees C) and the increased cation exchange of silver by zinc at higher temperatures strongly influence the optical properties of the resulting NCs. The correlation between synthesis parameters and resulting optical properties provided insights on the growth and stability of ternary and quaternary semiconductors. Systematic investigation with time-resolved spectroscopy showed distinguishable PL behaviors between developing and fully grown AIZS NCs. Attempts to coat as-prepared AgInS2 NCs resulted in the same PL behavior as the one-step reaction product indicating that Zn readily exchanges with Ag ions even when not directly incorporated in the initial reaction mixture. Even with a low amount of zinc, the fully grown AIZS NCs showed improved PL QYs and single exponential decay behavior with long PL lifetimes. Control of the optical properties of these NCs makes them potentially useful for applications in photovoltaics and bioimaging particularly in light of their nontoxicity.