Luminophores of tunable colors from ternary Ag–In–S and quaternary Ag–In–Zn–S nanocrystals covering the visible to near-infrared spectral range

Abstract

Ternary Ag–In–S or quaternary Ag–In–Zn–S nanocrystals were prepared from simple precursors (silver nitrate, indium(III) chloride, zinc stearate in a mixture of DDT and ODE) by injecting a solution of elemental sulfur into OLA. Ternary nanocrystals were modified by depositing either a ZnS or a CdS shell, yielding type I and type II core/shell systems exhibiting photoluminescence QY in the range of 12–16%. Careful optimization of the reaction conditions allowed alloyed quaternary Ag–In–Zn–S nanocrystals exhibiting tunable photoluminescence in the spectral range of 520–720 nm with a QY of 48% and 59% for green and red radiations, respectively, to be obtained. ¹H NMR analysis of the nanocrystal organic shell, after dissolution of its inorganic core, indicated that surfacial sulfur atoms were covalently bonded to aliphatic chains whereas surfacial cations were coordinated by amines and carboxylate anions. No thiol-type ligands were detected. Transfer of the prepared nanocrystals to water could be achieved in one step by exchanging the initial ligands for 11-mercaptoundecanoic ones resulting in a QY value of 31%. A new Ag–In–Zn–S nanocrystal preparation method was elaborated in which indium and zinc salts of fatty acids were used as cation precursors and DDT was replaced by thioacetamide. This original DDT-free method enabled similar tuning of the photoluminescence properties of the nanocrystals as in the previous method; however the measured photoluminescence QYs were three times lower. Hence, further optimization of the new method is required.