Structural and optical analysis of the role of modifier oxides in multi-component silicate glasses for laser applications

Multi-component silica calcium phosphate glasses doped with modifiers of alkaline and transition metal oxides of Mg²⁺, Fe³⁺, and Bi³⁺ were synthesized by the sol-gel method. The glasses were analyzed for structural behavior by XRD analysis. While alkaline metal-doped glasses were purely amorphous, the transition metal oxides induced fractional crystallinity in the material, with bismuth evidencing a highly glass-ceramic attribute. The FT-IR analysis confirmed the presence of the silicate and phosphate linkages in the glass material by the vibration modes around 790 cm^-1 and 450 cm^-1. The peaks also would represent the bridging and non-bridging oxygens of the glass formers. The UV-visible absorption spectra of the alkaline metal-infused glasses demonstrated the absence of sharp absorption peaks, while the transition metals-doped glasses evidenced prominent UV absorption. Tauc’s plots of the absorption spectra were employed to predict the band gap energies. While the Fe³⁺ doped glass exhibited the lowest band gap energy of 2.6 eV approaching a semiconducting nature, the remaining glasses expressed an insulating behavior with a value around 4 eV. The high UV absorption and lower bandgap indicates the suitability of the iron-doped glass for photovoltaic devices. Green and red emissions from all the glasses were observed by the photoluminescence analysis. While the emission is indicative of the nature of the glass host, the intensity of luminescence was altered by the influence of modifiers. The multi-component silicate glasses underscore the efficiency of the modifiers which could be suitably tailored for influencing the laser activity.