Tunable fluorescence emission of ternary nonstoichiometric Ag–In–S alloyed nanocrystals

Low toxic, nonstoichiometric colloidal Ag–In–S ternary quantum dots with different Ag content were synthesized by a one-pot hot-injection method based on the reaction of metal acetylacetonates with sulfur dissolved in octadecene. X-ray diffraction (XRD), transmission electron microscopy, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the size, structure, and morphology of these samples. ICP-MS was employed to analyze the compositions of Ag–In–S nanocrystals. The optical properties were characterized by UV–Vis absorption, photoluminescence (PL) spectroscopy, and time-resolved photoluminescence. Varying the fraction of cationic and capping agents, the compositions of Ag–In–S nanocrystals were precisely controlled. XRD and HRTEM results indicate the compositional homogeneity of Ag–In–S. The emission spectra across the different compositions exhibiting a single bandgap feature further confirm the formation of Ag–In–S alloy NCs, rather than phase separated Ag₂S and In₂S₃. Composition-dependent tunable PL emissions have been observed. The relative PL quantum yield is up to 16 %, which exhibited substantially enhanced comparing with the stoichiometric AgInS₂ semiconductor core QDs reported in previous literature. The PL decay curve of Ag–In–S has a biexponential characteristic, which indicates that the recombination of an electron and a hole is dominated by the surface defect and the recombination process associated with internal traps is reduced significantly. The large Stokes shift between the absorption peaks and their emissions should inhibit the reabsorption and Förster energy transfer between Ag–In–S nanocrystals, which provides the alternative in the further applications where high-concentrations of nanocrystals are needed.