Structural and photoluminescence characterisation of Tm³⁺-doped lithium calcium bismuth borate glasses for blue light-emitting application

This study reports the synthesis and characterisation of Tm³⁺-doped lithium calcium bismuth borate (LCBBTm) glasses (Tm³⁺: 0.25–1.0 mol%) prepared by melt-quenching. The physical and optical parameters exhibit systematic variation, with the refractive index increasing from 1.617 to 1.620 along with the enhanced electronic oxide polarizability. Raman analysis reveals a structural transformation from BO₃ to BO₄ units, associated with the borate anomaly. PL studies show strong blue emission at 454 nm under 359 nm excitation, corresponding to the ¹D₂ → ³F₄ transition of Tm³⁺ ions. The 0.5 mol% Tm³⁺-doped LCBB glass exhibits maximum emission intensity, while higher concentrations show concentration quenching due to non-radiative energy transfer. CIE chromaticity analysis confirms deep-blue emission with a colour purity of 79.2%, indicating the suitability of these glasses for advanced lighting technologies.