Investigation of uranium luminescence in SrB4O7 matrix by time resolved photoluminescence, thermally stimulated luminescence and electron spin resonance spectroscopy

• Optimization of U concentration for maximum PL yield and mechanism of quenching.
• Identification of the two types of uranium species (UO66-) present in the SBO matrix.
• Evaluation of the TSL trap parameters and the order of the kinetics.
• Formation of BOHC, BOEC and oxygen defect centers on gamma irradiation.
• Proposition of a plausible mechanism for the observed photo and thermo luminescence.

The luminescence of uranium in strontium borate (SrB4O7, SBO) matrix was investigated by time resolved photoluminescence, thermoluminescence (TSL) and electron spin resonance techniques (ESR). The samples were synthesized using solid state fusion reaction route and characterized by X-ray diffraction. Photoluminescence excitation and emission data suggested the stabilization of uranium as uranate (UO66-) in the matrix. Luminescence decay time data suggested the stabilization of uranium at two different sites in the matrix. By giving suitable delay times and choosing proper gate widths, the two emission spectra due to the two uranate species could be obtained. Thermoluminescence investigation on the gamma-rays irradiated sample showed a strong glow peak at ∼415 K and a weak glow peak at 505 K. The dose response behavior, the trap parameters along with the order of kinetics for the strong glow peak were determined. To pinpoint the exact chemical nature of the defect centers responsible for the observed glow peaks, electron spin resonance technique was employed. Based on the ESR-TSL correlation data and the observed photoluminescence results, a plausible mechanism for the origin of the luminescence in the system was proposed.

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