Studies on preparation and property evaluation of some Tm3+-ion doped oxyfluorophosphate glasses

• Preparation of Tm3+ doped fluoride-phosphate (FP) glasses.
• Studies of density, RI, IR, UV–vis and fluorescence spectra of the prepared glasses.
• The change of glass from metaphosphate (PO3−)n to P2(O,F)7 and P(O,F)4.
• Correlation of UV–vis band with nephelauxetic parameter.
• The low multiphonon relaxation rate in oxyfluorophosphate glasses.

The present paper reports the preparation of Tm3+ doped fluoride-phosphate (FP) glasses in the system of (100-18n) Ba(PO3)2 × n (2.0 MgF2 + 9.6 CaF2 + 6.4 AlF3), where n = 0.00, 2.00, 4.00 and 5.17. Various physical properties namely density, refractive index with special emphasis on the infrared (IR), ultraviolet–visible (UV–vis) absorption and fluorescence spectra of the prepared glasses has been systematically studied. The spectral studies reveal that upon addition of fluoride, the structure of the glass changes from metaphosphate (PO3−)n to P2(O,F)7 and P(O,F)4 in combination with the formation of Al(O,F)6, [AlF6]3− and [AlF4]−. The position of UV–vis absorption band has been correlated with quantitative calculation of nephelauxetic parameter and covalent bonding characteristics of the host. Appearance of two emission bands at ∼650 nm and ∼790 nm corresponds to 1G4 → 3F4 and 3H4 → 3H6 transitions, respectively. It is evident from the IR study that the fluorescence phenomena are expedited by the low multiphonon relaxation rate in oxyfluorophosphate glasses owing to their high intense low phonon energy (∼595 cm−1), which is very close to that of the fluoride glasses (500–600 cm−1).