Abstract <p>Thulium/holmium co-doped bismuth borotellurite glass have been prepared using melt quenching technique. All the prepared glasses characterized using X-ray Diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy at room temperature. There is no distinct peak in the XRD patterns over the observed range of 10° to 90°, indicating that all prepared glasses are amorphous. FTIR study reveals that the glass structure is composed of by TeO₃, TeO₄, BO₄, BO₃, BiO₃, and BiO₆ structural units. According to the bridging and non-bridging oxygen, the impact of the Ho₂O₃ addition was demonstrated by the calculated ratio of BO₄ to TeO₄ in the structural network. Bridging oxygen formation was proposed by the calculated ratio of BO₄ to TeO₄ increasing in along with the increase in Ho₂O₃ concentration (<i>x</i> = 0 to 1.0 mol %). Additionally, the declining ratio of BO₄ to TeO₄ (<i>x</i> = 1.5 to 2.5 mol %) explains the formation of non-bridging oxygen.</p>