Persistent photoluminescence emission from SrTa₂O₆:Pr³⁺ phosphor prepared at different temperatures

Phosphors with persistent emission are of interest for security and emergency signage, and medical diagnosis. Three SrTa₂O₆:Pr³⁺phosphor samples with persistent emission were prepared by solid state reaction at 1200, 1400 and 1500 °C. Structural crystallization was shown to improve with an increase in temperature as identified by X-ray diffraction. The scanning electron microscopy images showed that the particles of the phosphor were agglomerated and co-melting was induced by increasing the synthesis temperature. The ion distribution in the phosphors was determined using the time of flight secondary ion mass spectroscopy. The red emission was obtained from the D₂→³H₄ and the ³P₀→³H₆ transitions at 608 and 619 nm, respectively. The main absorption occurred at 225 nm (5.5 eV), and the band gap (E_g) calculations confirmed that it corresponds to band-to-band excitation. Another excitation due to charge transfer at 300 nm was also obtained which makes the phosphor suitable to be used in red light emitting diodes. The persistent emission time parameters (260-296 s) were calculated from the phosphorescence decay curves using the second order exponential decay equation. The corresponding electron trapping centers were determined using the thermoluminescence spectroscopy, and the activation energy was determined using the initial rise method.