Photoluminescence, thermally stimulated luminescence and electron paramagnetic resonance of europium-ion doped strontium pyrophosphate

Europium-ion doped strontium pyrophosphate was prepared via a chemical precipitation method to investigate the fluorescence of europium ions, the phosphate radical ions formed upon gamma-ray irradiation and their role in the thermally stimulated luminescence (TSL) of this compound. Fluorescence spectra revealed that europium ions were present in divalent as well as trivalent oxidation states. The measurements of fluorescence life time indicated that Eu³⁺ ions existed in two different types of environments in the lattice. Gamma irradiated europium-ion doped Sr₂P₂O₇ showed the presence of two thermo-luminescence glow peaks at 465 and 565 K; however, no glow was observed in the undoped sample. Electron paramagnetic resonance (EPR) studies of europium-ion doped samples showed signals from Mn²⁺ ions (present as impurity) prior to and after gamma irradiation. Upon gamma irradiation, signals originating from PO₂²⁻, PO₃²⁻ and O₂⁻ radical ions were observed in the undoped and doped samples. In the gamma irradiated europium-ion doped samples, additional low-field EPR signals, attributed to Eu²⁺ ions, were observed. By correlating the TSL and EPR results on europium-ion doped Sr₂P₂O₇, the mechanism for the glow peak at 565 K was identified.