Novel Eu-Doped Glasses in the MoO-WO-LaO-BO System: Preparation, Structure and Photoluminescent Properties.

Novel multicomponent glasses with nominal compositions of (50-x)MoO:xWO:25LaO:25BO, x = 0, 10, 20, 30, 40, 50 mol% doped with 3 mol % EuO were prepared using a conventional melt-quenching method. Their structure, thermal behavior and luminescent properties were investigated by Raman spectroscopy, differential thermal analysis and photoluminescence spectroscopy. The optical properties of the glasses were investigated by UV-vis absorption spectroscopy and a determination of the refractive index. Physical parameters such as density, molar volume, oxygen molar volume and oxygen packing density were determined. The glasses are characterized by a high glass transition temperature. Raman analysis revealed that the glass structure is built up mainly from tetrahedral (MoO) and (WO) units providing Raman bands of around 317 cm, 341-352 cm, 832-820 cm and 928-935 cm. At the same time, with the replacement of MoO with WO some fraction of WO octahedra are produced, the number of which increases with the increasing WO content. A strong red emission from the D level of Eu ions was registered under near-UV (397 nm) excitation using the F → L transition of Eu. Photoluminescence (PL) emission gradually increases with increasing WO content, evidencing that WO is a more appropriate component than MoO. The integrated fluorescence intensity ratio R (D → F/D → F) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu in non-centrosymmetric sites. All findings suggest that the investigated glasses are potential candidates for red light-emitting phosphors.