Local structure and energy transfer of Gd3+ to Dy3+ in phosphate-based glasses

Abstract

The phosphate-based glasses doped with Gd3+ and Dy3+ ions were fabricated by melt quenching at 1200 °C. The physical, structural, and luminescence properties that would suggest they are potential candidates for scintillating materials have been examined. The density and molar volume of glasses increase with increasing Gd3+ concentration. The absorption peaks indicate the Dy3+ energy transition from the 6H15/2 ground state to several excited states such as 6P7/2 (350 nm), 6P3/2 (364 nm), 6F7/2 (387 nm), 6G11/2 (426 nm), 6I15/2 (452 nm), 6F5/2 (807 nm), 6F7/2 (906 nm), 6F9/2 (1100 nm), 6H9/2 (1285 nm), and 6H11/2 (1697 nm), respectively. According to the findings, when compared to a commercially available BGO crystal, the highest value of x-ray luminescence spectrum intensity was observed at 17 mol% of Gd2O3, with 15.42% of the integral scintillation efficiency. However, the photoluminescence spectra show the maximum value at 13 mol% of Gd2O3 content with excited at 275 nm and 350 nm, while the decay time (τ) tends to decrease with increasing Gd2O3 content. Interestingly, the local structure study was conducted through XANES and EXAFS analysis to understand the local environment of Gd and Dy atoms. The XANES result indicated that the oxidation states of the Gd and Dy ions in the sample glass were +3. The EXAFS fitting parameters showed Debye-Waller factors (σ2) of 17 mol% of Gd2O3 as the highest value that represents a more asymmetric environment around Gd/Dy. Moreover, the EXAFS fitting indicates a short distance of Gd–Gd at 13 mol% Gd2O3 content is indicative of their efficient internal energy transfer between Gd–Gd.