The role of sulfate ions on distinctive defect emissions in ZnO:Ce3+ nanophosphors - A study on the application in color display systems

Abstract

The conventional solid-state reaction route was used to synthesize a series of SO42− (1.0 mol %) and Ce3+ (0.5, 1.0, 1.5, 2.0, and 2.5 mol%) encapsulated ZnO nanophosphors. The powder X-ray diffraction confirmed the formation of the hexagonal wurtzite structures of ZnO showing that the main crystal structure was not influenced by the low concentrations of Ce3+ and SO42− ions. The effect of sulfate ions on the defect-induced photoluminescence (PL) emission of ZnO was identified in deconvoluted PL bands and was found to correlate with the shifts observed in the band edges of the absorption spectra. Defect‐related emissions such as near‐band edge and deep-level emission were detected from undoped ZnO and ZnO–SO4 and ZnO–SO4:Ce3+ (1.0%) PL spectra. The well-known emission from Ce3+ associated with the 5D4−4Fj transitions was suppressed in the ZnO:Ce3+, while the incorporation of SO4 cations was shown to increase the defects related emission in ZnO considerably. The increase in the PL intensity was attributed to non-radiative energy transfer from SO42− to defect levels in ZnO. The proposed mechanisms of energy transfer and related electronic transitions leading to photoemission are presented. The Commission Internationale de l’Eclairage (CIE - 1931) coordinates and the correlated colour temperature and color-purity data suggest that the ZnO–SO4 and ZnO–SO4:Ce3+ phosphors hold a significant promise for applications in displays.