Tm3+ Ion Blue Emission Quenching by Pd2+ Ions in Barium Phosphate Glasses: Fundamental Analysis toward Sensing Applications.

Abstract

The quenching effect of Pd2+ ions on the blue emission from Tm3+ was investigated for the first time using barium phosphate glass as model matrix. Glasses containing fixed Tm2O3 at 0.5 mol % and PdO up to 0.3 mol % (added relative to P2O5) were prepared by melting and first characterized for basic structural properties by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy. Thermal properties were then evaluated by differential scanning calorimetry (DSC). The focus was thereafter on evaluating the optical properties by absorption and photoluminescence (PL) spectroscopy with decay kinetics assessment. XRD confirmed the amorphous nature of the glasses synthesized. The vibrational spectroscopy assessment consistently exhibited the IR- and Raman-active bands characteristic of phosphate glasses, showing no significant variation with PdO codoping. The DSC analysis revealed all glasses possessed high thermal stability assessed by the differences (ΔT = Tg - Tx ≥ 154 °C) between glass transition temperatures (Tg) and onset of crystallization (Tx). A tendency of the Tg values to increase with PdO contents was however exhibited. In addition, specific enthalpies of crystallization showed magnitudes decreasing with increasing PdO concentration, thus suggesting crystallization suppression by Pd2+. Concerning the optical properties, it was observed that codoping the glasses with PdO (0.1-0.3 mol %) led to the development of the visible Pd2+ d-d absorption band (peak ≈415-410 nm). In addition, drastic PL quenching of the Tm3+ blue emission around 452 nm (1D2 → 3F4 transition) was induced by Pd2+. Analyzing PL decay curves obtained by exciting Tm3+ ions at 359 nm while monitoring 452 nm emission revealed decreased 1D2 state lifetimes. Thus, a potential of Tm3+ for analytical sensing of Pd2+ in various matrices was suggested. Ultimately determining quenching constants from the PL data and based on the comparison of results from emission intensity and decay rates, likely Tm3+ → Pd2+ energy transfer processes underlying the PL quenching were proposed.