Structure and Luminescent Properties of Niobium-Modified ZnO-B₂O₃:Eu³⁺ Glass

The effect of the addition of Nb₂O₅ (up to 5 mol%) on the structure and luminescent properties of ZnO-B₂O₃ glass doped with 0.5 mol% (1.32 × 10²²) Eu₂O₃ was investigated by applying infrared (IR), Raman and photoluminescence (PL) spectroscopy. Through differential thermal analysis and density measurements, various physical properties such as molar volume, oxygen packing density and glass transition temperature were determined. IR and Raman spectra revealed that niobium ions enter into the base zinc borate glass structure as NbO₄ tetrahedra and NbO₆ octahedra. A strong red emission from the ⁵D₀ level of Eu³⁺ ions was registered under near UV (392 nm) excitation using the ⁷F₀ → ⁵L₆ transition of Eu³⁺. The integrated fluorescence intensity ratio R (⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu³⁺ in non-centrosymmetric sites. The higher Eu³⁺ luminescence emission observed in zinc borate glasses containing 1-5 mol% Nb₂O₅ compared to the Nb₂O₅-free zinc borate glass evidences that Nb₂O₅ is an appropriate component for modifying the host glass structure and improving the emission intensity.