An experimental and theoretical study on the photoluminescence of O and Br co-doped ZnS quantum dots synthesized by a solid-state reaction method

Abstract

ZnS and ZnS0.96-xO0.04Brx (0 ≤ x ≤ 0.07) quantum dots (QDs) were synthesized via a solid-state reaction method at low temperature. The effects O and Br co-doping on the crystal structure, particle size, morphology, chemical state, energetic and electronic properties, and photoluminescence (PL) of ZnS QDs were researched by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflection and PL spectra combining with first-principles calculations, respectively. The results showed that all samples had a cubic blend structure, and the average crystallite size was about 3.3–4.5 nm. The band gap of ZnS QDs was widened from 3.64 to 3.76 eV by O and Br co-doping, and the blue shift of emission peak was observed. It indicated that the luminescence intensity was strengthened after co-doping, and ZnS0.93O0.04Br0.03 QDs showed the strongest emission, which was about 9 and 2.5 times stronger than that of ZnS and ZnS0.96O0.04 QDs, respectively. First-principles calculations were used to explain the origin of high PL intensity, and the results implied that both O and Br effectively enhanced the density of electron carries.