Enhancement Mechanism of the Photoluminescence Quantum Yield in Highly Efficient ZnS–AgIn5S8 Quantum Dots with Core/Shell Structures

Abstract

The optical properties of ZnS–AgIn5S8 quantum dots (QDs) with core/shell structures are examined to clarify the enhancement mechanism of the photoluminescence (PL) quantum yield (QY). Two types of QDs are synthesized by varying the concentration of zinc precursors, with alloyed-core (ZnS–AgIn5S8, ZAIS), inner-shell (ZnIn2S4, ZIS), and outer-shell (ZnS) structures, such as ZAIS/ZIS/ZnS and ZAIS/ZnS. Upon alloying/shelling processes from the preformed AgIn5S8 QDs, the evolution of the band gap energy indicates the formation of the solid solution of ZAIS. Due to the difference in the degree of alloying between ZAIS/ZIS/ZnS and ZAIS/ZnS QDs, the blue shift of PL, Stokes shift, and QY are different. The alloying/shelling processes improve the QY of the intrinsic defect states more effectively than the QY of the surface defect states, while the time-resolved studies suggest that the enhanced radiative rate of the intrinsic states is responsible for the improvement of the QY, in addition to the reduced nonradiat...