Tm 3+ Ion Blue Emission Quenching by Pd 2+ Ions in Barium Phosphate Glasses: Fundamental Analysis toward Sensing Applications.

The quenching effect of Pd 2+ ions on the blue emission from Tm 3+ was investigated for the first time using barium phosphate glass as model matrix. Glasses containing fixed Tm 2 O 3 at 0.5 mol % and PdO up to 0.3 mol % (added relative to P 2 O 5 ) 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 (Δ T = T g - T x ≥ 154 °C) between glass transition temperatures ( T g ) and onset of crystallization ( T x ). A tendency of the T g 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 Pd 2+ . 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 Pd 2+ d-d absorption band (peak ≈415-410 nm). In addition, drastic PL quenching of the Tm 3+ blue emission around 452 nm ( 1 D 2 → 3 F 4 transition) was induced by Pd 2+ . Analyzing PL decay curves obtained by exciting Tm 3+ ions at 359 nm while monitoring 452 nm emission revealed decreased 1 D 2 state lifetimes. Thus, a potential of Tm 3+ for analytical sensing of Pd 2+ 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 Tm 3+ → Pd 2+ energy transfer processes underlying the PL quenching were proposed.