Synthesis and Luminescent Properties of Eu3+-Doped Complex Borosilicate Glasses

Glasses with compositions (52.5 − x/2)B2O3:(12.5 − x/2)SiO2:25La2O3:5ZnO:5CaO:0.5Eu2O3:xWO3, x = 0, 2.5, 5, 7.5, 10, 20 (mol%) were prepared by conventional melt-quenching method and investigated by X-ray diffraction analysis, DSC analysis, DR-UV-Vis spectroscopy and photoluminescence spectroscopy. Physical parameters like density, molar volume, oxygen molar volume and oxygen packing density were also determined. Their values, as well as DR-UV-Vis spectroscopy results, indicate that the tungstate ions incorporate into the base borosilicate glass as tetrahedral WO4 and octahedral WO6 groups. With increasing WO3 content over 5 mol%, WO6 units are progressively linked to each other by W-O-W bonds, leading to the formation of a more connected and homogeneous glass network. Glasses are characterized by a high glass transition temperature (over 650 °C) and good thermal stability. The emission intensity of the Eu3+ ion increases with the introduction of WO3 due to the occurrence of non-radiative energy transfer from the tungstate groups to the active ion. The most intense luminescence peak observed at 612 nm suggests that the glasses are potential materials for red emission.