Improved electroluminescence performance of ZnS:Cu,Cl phosphors by ultrasonic treatment

ZnS:Cu,Cl electroluminescence (EL) phosphors were prepared by high-temperature (1150 °C) solid-state reaction, subsequent ultrasonic treatment (t=0-60 min) and final low-temperature annealing process at 750 °C. The as-synthesized phosphors were characterized by X-ray powder diffraction (XRD), UV-vis absorbance spectra, electron probe microanalyzer (EPMA) and photoluminescence (PL) spectra. EL performance was investigated on an EL lamp fabricated by screen-printing at 100 V and 400 Hz. Ultrasound irradiation leads to intensity reductions and width increases of some XRD diffraction peaks, and results in a slight red-shift of UV-vis absorption edge. It also exhibits strong influences on PL and EL properties of the phosphors. Generally, PL performance monotonically declines with the increase of ultrasonic time, while EL performance benefits from the ultrasonic treatment and is superior to that of the commercial ones. The defects in the microstructure induced by the ultrasonic treatment are the fundamental reason for the change of PL and EL performances.