Luminescent dynamics of Pr³⁺ in MTaO₄ hosts (M=Y, la or Gd)

Luminescence characteristics including fluorescence, phosphorescence, and thermoluminescence of Pr³⁺ in orthotantalate host matrices are presented. X-ray diffraction (XRD) spectra indicate that MTaO ₄:Pr³⁺ (M=Gd, Ta and Y) phosphor materials were successfully prepared at 1200 C using the solid state reaction method. Red and blue-green emissions were observed from the three phosphors when they were characterised using the DESY synchrotron radiation. A simplified energy transfer scheme explaining energy transfer from the TaO₄ group to either Gd³⁺ states in the GdTaO₄:Pr³⁺ system or directly to Pr³⁺ states in LaTaO₄:Pr³⁺ and YTaO₄:Pr³⁺ systems is presented. Afterglow measurements were carried out after UV exposure at room temperature and the phosphorescence decay curves suggest multi-exponential decay behaviour consisting of the slow and fast components following the order; GdTaO₄:Pr ³⁺<LaTaO₄:Pr³⁺<YTaO₄:Pr ³⁺. Thermoluminescence measurements reveal broad glow curve patterns indicating a quasi-continuous trap distribution in the tantalate phosphors.