Study on the reducing effect of γ-irradiation on Sm³⁺ doped LiAl fluorophosphate glasses through optical, structural and luminescence analysis

Undoped and (0.2, 0.5, 1, 3%) Sm₂O₃-dopants within host LiAl fluorophosphate glasses of the basic composition mol% (P₂O₅ 70, LiF 20, AlF₃ 10) were prepared. The glasses were characterized by studying their optical, FT infrared and photoluminescence spectra before and after successive γ-radiation (0.25, 1, 3 Mrad). The strong absorption in the UV wavelength region of the optical spectra has been related to trace iron impurity. The Sm³⁺ ions reveal their characteristic peaks arranged into two groups from about 330 to 460 nm and from 950 to 1550 nm. The major spectra of Sm³⁺ ions are assumed to be due to transitions from ⁶H_5/2 level to various excited ^2s+1L_j levels. The photoluminescence spectra show four emission lines at 560, 596, 642 and 702 nm and their intensities increase with Sm₂O₃ content. Gamma irradiation produces limited variations in the optical spectra. Examinations of the excitation and emission spectra of the studied glasses at λ_em = 600 and λ_ex = 402 nm show results supporting the stability of Sm³⁺ ions after gamma irradiation. However, the change of the excitation wavelength to λ_ex = 535 nm reveals the appearance of two additional peaks which are related to partial reduction of some Sm³⁺ ions to Sm²⁺ ions through suggested photoreduction by capturing librated electrons during the radiation process. FTIR spectra of the studied glasses reveal similar vibrational modes related to Q² and Q³ phosphate groups due to the high content of P₂O₅ in the glass composition (70 mol%) together with some suggested mixed fluorophosphate groups (PO₃F)²⁻. Gamma irradiation shows limited variations in the FTIR spectra due to the proposed presence of AlF₄ and/or AlF₆ groups which conduct stability to the glass network.