Spectroscopic and Thermographic Qualities of Praseodymium-Doped Oxyfluorotellurite Glasses

The thermal stability of oxyfluorotellurite glass systems, (65-x)TeO₂-20ZnF₂-12PbO-3Nb₂O₅-xPr₂O₃, doped with praseodymium was examined. The different concentrations of praseodymium oxide (x = 0.5 and 2 mol%) were applied to verify the thermal, optical and luminescence properties of the materials under study. The relatively high values of the Dietzel (ΔT) and Saad-Poulain (S or H') thermal stability factors determined using a differential thermal analysis (DTA) indicate the good thermal stability of the glass matrix, which gradually improves with the content of the active dopant. The temperature dependence of optical spectra in the temperature range 300-675 K for the VIS-NIR region was investigated. The involved Pr³⁺ optical transition intensities and relaxation dynamic of the praseodymium luminescent level were determined. The ultrashort femtosecond pulses were utilized to examine a dynamic relaxation of the praseodymium luminescent levels. Although the measured emission of the Pr³⁺ active ions in the studied glass encompasses the quite broad spectral region, the observed luminescence may only be attributed to ³P_J excited states. As a result, the observed decrease in the experimental lifetime for the ³P₀ level along with the increasing activator content was identified as an intensification of the Pr-Pr interplay and the associated self-quenching process. The maximum relative sensitivities (S_r) estimated over a relatively wide temperature range are ~0.46% K^-1 (at 300 K) for FIR (I₅₃₀/I₄₉₇) and 0.20% K^-1 (at 600 K) for FIR (I₆₃₀/I₄₉₇), which seems to confirm the possibility of using investigated glasses in optical temperature sensors.