Thulium-doped magnesium borotellurite glasses: Fabrication, optical properties and photoluminescence performance

• New thulium-doped magnesium borotellurite glass system has been successfully fabricated using melt-quenching method. • Increasing Tm₂O₃ concentration caused a reduction in direct (2.825 → 2.149 eV) and indirect (2.103 → 1.669 eV) band gaps. • Urbach energy and refractive index increased with progress of Tm₂O₃ concentration. • Photoluminescence revealed strong blue emission at 455 nm, aligning with the CIE chromaticity diagram. Thulium-doped magnesium borotellurite glass with the empirical composition of x (Tm 2 O 3 )–10MgO–30B 2 O 3 –(60- x )TeO 2 where x ranges from 0.0 to 3.0 mol%, was successfully synthesized via the conventional melt-quenching technique. FTIR analysis confirmed the presence of Te O 2 , B O 3 , and B O 4 structural units within the glass network, along with the formation of bridging oxygen bonds. The amorphous nature of the glass was verified by XRD patterns, as indicated by the absence of sharp diffraction peaks. Optical properties were found to vary with the concentration of T m 2 O 3 . Both the direct and indirect optical band gaps decreased from 2.825 eV to 2.149 eV and from 2.103 eV to 1.669 eV respectively. The obtained value for refractive index is between 2.693 to 2.896 while the Urbach energy is from 0.455 eV to 1.548 eV. The trend in refractive index showed an inverse relationship to the band gap and Urbach energy, attributed to changes in non-bridging oxygen content, increased cross-linking density and the presence of free electrons within the glass matrix. The optical absorption spectra exhibited four prominent transitions corresponding to the at 3 H 5 , 3 F 3 , 1 G 4 and 1 D 2 excited states originating from the ground state 3 H 6. Photoluminescence measurements revealed three distinct emission peaks with the strongest emission observed at 455 nm which is consistent with the blue region confirmed through CIE chromaticity analysis.