Structural and Luminescent Properties of WO3-Modified Eu3+-Doped Borosilicate Glasses

In this study, the influences of WO3 on the structure, thermal behavior and luminescent characteristics of Eu3+-doped borosilicate glasses with compositions (35 − x/2)B2O3:(35 − x/2)SiO2:25La2O3:5CaO:0.5Eu2O3:xWO3, x = 0, 5, 10, and 15 mol% have been studied via X-ray and neutron diffraction (XRD, ND) combined with reverse Monte Carlo (RMC) modeling, infrared spectroscopy (IR), differential scanning calorimetry (DSC), photoluminescence (PL) spectroscopy and density measurements. IR and RMC structural modeling reveal that the glass network consists of SiO4 tetrahedra with non-bridging oxygen (Q2); diborate, pyroborate and metaborate units; [WO4]2− and WO6 groups; and Si-O-W, Si-O-B, B-O-B and W-O-W linkages. Structural and density analyses show that incorporating up to 10 mol% WO3 increases structural disorder, depolymerizes the silicate matrix, and creates non-bridging oxygens (NBOs). In contrast, at 15 mol% WO3, the network exhibits crosslinking due to the development of interconnected, polymerized WO6 octahedra. Thermal investigations demonstrate exceptionally high glass transition temperatures (Tg > 700 °C) and notable thermal stability, as no crystallization occurred up to 800 °C in any sample. The slight decrease in Tg to 718 °C at 15 mol% WO3 validates network “softening” driven by the formation of polymerized WO6 octahedral structural units. Photoluminescence spectra showed a strong red emission at 612 nm from the 5D0→7F2 transition of Eu3+ under near-UV (392 nm) excitation. It was established that the addition of WO3 to borosilicate glasses leads to improvement of the emission properties of the active ion through structural modification. These results demonstrate that the optimized glass compositions hold potential for use as red phosphor materials.