This paper reports the preparation of Tm3+ doped fluoride-phosphate (FP) glasses in the system (100-18n) Ba(PO3)2xn(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 ~650nm and ~790nm 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 miltiphonon relaxation rate in oxyfluorophosphate glasses owing to their high intense low phonon energy (~595cm-1), which is very close to that of the fluoride glasses (500-600cm-1).
