Investigating Photoluminescence Mechanism of Cu-doped Zn–In–Se Quantum Dots by Zn/In Ratio

Abstract

We investigate the composition-dependent photoluminescence (PL) spectra of Cu-doped Zn–In–Se quantum dots (QDs) to determine the mechanism of radiative recombination of the interband transition. As the Zn/In ratio increases, a systematic blue shift in the dominant broad emission occurs from 648 to 552 nm, with a fixed narrow peak at 465 nm. Based on the nearly constant 3.2 nm nanoparticle size, as determined by high-resolution transmission electron microscopy, the quantum size effect of the Zn/In ratio can be excluded. X-ray diffraction and Raman results demonstrate the formation of multiple phases including ZnIn2Se4, ZnSe, and In2Se3 in all samples, as well as Cu2+ ions occupying Zn2+ sites in the QD lattice. The band structure in the Cu-doped Zn–In–Se QDs is determined via UV–vis absorption spectra and cyclic voltammetry curves, and the defect levels in the gap are identified by use of PL and PL excitation spectra. The enhanced 465 nm emission is ascribed to zinc interstitial (Zni) defects in the increa...