Influence of rare Earth doping and modifier oxides on optical and thermoluminescence properties of tellurite glasses for radiation dosimetry applications

Glasses with the composition ZnF₂-MO-TeO₂:Ln₂O₃ (where M represents Zn, Cd, and Pb, and Ln represents Pr, Eu, Ho, and Er) were prepared using the melt-quench-anneal method. Absorption spectra were recorded for both undoped and rare-earth doped glasses. Judd-Ofelt (J-O) intensity parameters (Ω2, Ω4, and Ω6) were determined from the spectra of the rare-earth doped glasses. The Ω2 values were observed to be higher in ZnO-modified glasses and lower in PbO-modified glasses, indicating more asymmetric and covalent environments for Ln³⁺ ions in ZnO-modified glasses. Among the modified series, Ho³⁺ doped glasses showed lower values of Ω4 and Ω6, which is attributed to their significantly lower vibrational frequencies. Thermoluminescence (TL) characteristics of X-ray irradiated pure and Ln³⁺-doped tellurite-modified glasses were studied in the temperature range of 297-473 K. Undoped glasses containing zinc, cadmium, and lead oxides exhibited single TL peaks at 423 K, 389 K, and 376 K, respectively. No additional peaks were observed upon rare-earth ion doping; however, the existing glow peak temperatures gradually shifted towards higher temperatures with an increase in the intensity of the TL light output. Among the rare-earth doped glasses, the TL light output was found to be maximum in Ho³⁺ containing any modifier. The observed TL results were discussed in light of J-O intensity parameters, showing that Ω4 and Ω6 are more critical than Ω2 in optimizing the thermoluminescence properties of rare-earth-doped tellurite glasses. The trap depth parameters associated with the observed TL peaks were evaluated using Chen's formulae. These parameters suggest the potential applicability of Ho³⁺ ions doped glasses in radiation dosimetry applications.