Luminescence properties of ZnS：Cu, Eu semiconductor nanocrystals synthesized by a hydrothermal process

ZnS:Cu, Eu nanocrystals with an average diameter of ～ 80 nm are synthesized using a hydrothermal approach at 200 ℃. The photoluminescence (PL) properties of the ZnS:Cu, Eu nanocrystals before and after annealing, as well as the doping form of Eu, are studied. The as-synthesized samples are characterized by X-ray diffraction, scanning electron microscopy, inductively coupled plasma-atomic emission spectrometry, and the excitation and emission spectra (PL). The results show that both Cu and Eu are indeed incorporated into the ZnS matrix. Compared with the PL spectrum of the Cu mono-doped sample, the PL emission intensity of the Cu and Eu-codoped sample increases and a peak appears at 516 nm, indicating that Eu³⁺ ions, which act as an impurity compensator and activator, are incorporated into the ZnS matrix, forming a donor level. Compared with the unannealed sample, the annealed one has an increased PL emission intensity and the peak position has a blue shift of 56 nm from 516 nm to 460 nm, which means that Eu³⁺ ions reduce to Eu²⁺ ions, thereby leading to the appearance of Eu²⁺ characteristic emission and generating effective host-to-Eu²⁺ energy transfer. The results indicate the potential applications of ZnS:Cu, Eu nanoparticles in optoelectronic devices.