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

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 ⁵D₄−⁴F_j 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.