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

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 ⁶H_15/2 ground state to several excited states such as ⁶P_7/2 (350 nm), ⁶P_3/2 (364 nm), ⁶F_7/2 (387 nm), ⁶G_11/2 (426 nm), ⁶I_15/2 (452 nm), ⁶F_5/2 (807 nm), ⁶F_7/2 (906 nm), ⁶F_9/2 (1100 nm), ⁶H_9/2 (1285 nm), and ⁶H_11/2 (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.