Copper concentration dependence of structure, morphology and optical properties of ZnS:Cu,Cl phosphor powder

Abstract

ZnS:Cu,Cl phosphors were prepared by firing ZnS powder with 1 wt% NaCl and CuS nanocrystallites in the range of 40–5000 ppm at 900 °C for 2 h in an atmosphere of 3% H 2/Ar and sulfur vapor. The particle size and structure of the ZnS:Cu,Cl powders were found to depend on the Cu concentration. The powders with Cu⩾400 ppm exhibited a cubic structure and were approximately 5 μm in size as compared to the hexagonal structure of those with less Cu additions (∼2 μm). The difference, resulting from the precipitation of Cu x S in the powders as determined by X-ray photoelectron and diffuse reflectivity analyses, revealed that the powders with Cu>400 ppm showed the Cu 2p main peaks and higher absorbance in the UV–vis region due to the wide range of the bandgap energy of Cu x S (1.2–1.75 eV). Electroluminescence (EL) consisting of blue, self-activated (SA) and green emission peaking at 440, 470 and 510 nm, was observed only in the powders with Cu⩾400 ppm. Besides the activator concentration quenching effect, the variation of EL intensity with the Cu concentration was elucidated to result the from amount of Cu x S precipitates as well as charge carriers in the powders.