Synthesis and characterization of Zn1−xCdxS:Cu, Cl red electroluminescent phosphor powders

Red electroluminescent (EL) phosphors of Zn1−xCdxS:Cu, Cl (x = 0–0.9) were prepared by a solid state reaction at 900 °C for 2 h in a reducing atmosphere. X-ray diffraction (XRD) analysis showed that the structure of Zn1−xCdxS:Cu, Cl (Cu: 800 ppm) transformed from cubic to hexagonal as x increased to 0.2. The stoichiometric composition of these alloy powders, revealed from the XRD and Raman measurements, was very close to the mixing molar ratio of ZnS to CdS according to Vegard's law and Raman shifting behavior. Meanwhile, based on the observation of the absence of CuxS by Raman scattering in the above samples (x > 0.3), we supposed that the increased Cu solubility with Cd contents was caused from the larger lattice constants by alloying Cd2+. In addition, the unavailability of CuxS to induce the structure transformation to cubic in the alloy powders with higher Cu additions (>800 ppm) may be due to the fact that Zn1−xCdxS stabilized in a hexagonal structure. In the luminescence measurements, the EL in the samples (x = 0.6–0.7) with or without CuxS precipitates was ascribed to both CuxS precipitates and local composition fluctuation (x).