Physical, structural, and optical properties of BaF₂-doped Li₂O-SrO-B₂O₃oxyfluoride glasses for UV-A luminescence

In this study, oxyfluoride glasses with chemical composition of 50B₂O₃-25Li₂O-(25–x) SrO-xBaF₂ (x = 0, 5, 10, 15, 20 and 25 mol%) were prepared through the convenient melt quenching method. X-ray diffraction analysis confirms the amorphous nature of the glass samples. The calculated physical parameters such as density, molar volume, average boron-boron separation, ion concentration and inter ionic distance provided the information about the structural stability of glass samples. FTIR spectra as well as molar volume calculations proved the formation of more non-bridging oxygens (NBO's) in presence for 0,5 and 10 mol% BaF₂ beyond 15 mol% the glass structure get changes and as a result NBO's starts to decrease for 20 and 25 mol%. The optical properties were measured using UV–visible spectroscopy in the range 200–800 nm at room temperature. Four absorption peaks are found at ∼228, ∼274, ∼350 and ∼470 nm. Amongst the peak at 274 nm is the most intense and sharp which is confirmed by the deconvoluted spectra. The wavelength between 300 and 450 nm the absorption peak shifts towards lower wavelength as a result the optical activity alters in the glasses. Photoluminescence spectra reveal a prominent emission peak around 390 nm. The emission intensity increased optimally for intermediate BaF₂ concentrations (10–20 mol%) due to the suppression of multiphonon relaxation by F⁻ions, but decreased at higher substitution levels as a result of concentration quenching. The decay profiles showed clear biexponential behaviour, confirming the coexistence of both radiative and non-radiative pathways, with lifetime values exhibiting strong correlation with PL intensity trends. Commission Internationale de I'Eclairage (CIE) and correlated colour temperature (CCT) studies indicate the glasses samples emit warm daylight in the ultra violet-A (UV-A) regions between 1979 and 1972.42K.