Photoluminescence, optical and structural properties of Pr3+-doped fluorophosphate glasses and their induced defects by gamma irradiation

Multicomponent fluorophosphate host glass and samples containing Pr2O3 as dopant oxide with added (0.25, 0.5, 1.0 or 2 wt%) were prepared by melting and annealing technique. Multiple characterization techniques were employed to investigate optical, photoluminescence and FTIR spectral properties of the prepared glasses before and after being gamma irradiated with doses of 2, 9 Mrad. Optical absorption spectra reveal only distinct UV absorption in the undoped glass which is related to trace iron impurities while the Pr2O3-doped samples exhibit two series of characteristic extended peaks within the visible and near-IR regions which are due to absorption of Pr3+ ions. Gamma irradiation causes a continuous increase of the intensity of the UV absorption with irradiation. The Pr2O3-doped samples reveal obvious effects including the shift of the absorption to longer wavelength only of the first visible series of absorption peaks while the second series of peaks in the near IR region remain almost unchanged. These optical changes upon irradiation are suggested to be related to photochemical reactions with the liberated pairs of electrons and positive holes during the irradiation process. Photoluminescence (PL) measurements indicate the appearance of five emission peaks and three excited peaks before irradiation and their intensities increase with the Pr2O3 content. With irradiation, the PL spectra reveal limited changes with 2 Mrad but with 9 Mrad, the first emission peaks show few variations but the main high intense peak at 600 nm remains unchanged but the intensities of the peaks become very close with the increase of Pr2O3 content. The PL results support the stability of the Pr3+ ions as evidenced by the persistence of the optical absorption spectra. FTIR spectra of the studied glasses reveal the appearance of repetitive vibrational bands due to main building PO4 units mainly with Q(2) and Q(3) units with some suggested fluorophosphates groups (PO3F)(-) AlF4 (AlFO) groups. Gamma irradiation decreases the intensities of some bands together with the generation of a distinct band at 1455 cm(-1). The FTIR results indicate the maintenance of the vibratonal bands after irradiation and the changes in the intensity of some bands are related to suggested variations in the bond angles and/or bond lengths of structural phosphate groups.