Seeded-mediated growth of ternary Ag–In–S and quaternary Ag–In–Zn–S nanocrystals from binary Ag2S seeds and the composition-tunable optical properties

Abstract

Herein, we demonstrated a seed-mediated growth method for the synthesis of ternary AgInS₂ (AIS) and quaternary Ag–In–Zn–S (AIZS) nanocrystals (NCs) by means of a partial cation exchange with In³⁺ and Zn²⁺ ions. Binary Ag₂S NCs with different sizes were synthesized first, which then acted as the seeds to prepare different-sized AIS NCs through the incorporation of In³⁺. The formation mechanism of AIS NCs was studied in terms of the temporal evolution of the morphology and crystal structure, and the heterostructured Ag₂S-AIS NCs were formed as intermediates during the growth process of AIS NCs. Variation in the Ag/In feeding ratios from 1 : 1 to 1 : 3 led to a broad tuning of the optical band gap and photoluminescence (PL) maximum of AIS NCs, in which very small-sized AIS NCs with a tetragonal phase were obtained. Subsequently, the incorporation of Zn²⁺ into AIS NCs resulted in the widening of the optical band gap and the shift of the PL maximum to higher energy with the enhancement of the absolute PL quantum yields (PLQYs). When the reaction temperature was increased, the PL emission maximum could be tuned from 2.04 to 2.33 eV and the absolute PLQYs could be tuned from 16% to 58%. Time-resolved PL spectroscopy was used to study the PL decay dynamics of the AIS and AIZS NCs, and the PL emission was related to the recombination of the surface-related states, intrinsic defects and donor–acceptor (D–A) pairs. The ternary and quaternary Ag-based semiconductor NCs have long-lived excitons, which may have promising applications in the field of energy conversion.