The structural and spectroscopic properties of
Na2O-Al2O3-SiO2-xP2O5
glasses (x=0 to 7 mol%) are investigated. Both Raman and IR spectra reveal that
discrete phosphate species ([PO4-3,
[PO3O1/2]-2) with low polymerization degree can
be formed in the silicate glass. These phosphate structures scavenge non-bridging
oxygen ions and cations from the silicate network, resulting in an increase of the
glass transition temperature. According to the Judd-Ofelt intensity parameters
(Ω2, Ω4, Ω6) of
Er3+, the asymmetry of local environment around Er3+
becomes higher, and the bond covalency between Er3+ and O2-
decreases after P2O5 is introduced. In the emission spectra,
photoluminescence intensity increases with increasing P2O5
concentration and the spectra are inhomogeneously broadened, revealing that the
ligand electric field around Er3+ is dramatically changed, and the glass
matrix becomes disordered.