Pd²⁺-induced quenching of the UV emission from Gd³⁺ ions in phosphate glass

This paper reports on the influence of Pd²⁺ ions on the ultraviolet emission from Gd³⁺, investigated in barium phosphate glass as model matrix. The glasses were prepared by the melting technique and characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, optical absorption, and photoluminescence (PL) spectroscopy including decay kinetics assessment. The XRD data confirmed the amorphous nature of the glasses, whereas FT-IR spectra indicated the basic structural features of PO₄ tetrahedra. The optical absorption analysis showed that addition of PdO up to 0.3 mol% lead to significant growth of the visible Pd²⁺ d-d absorption band around 415 nm, with ultimately some decrease in the optical band gap energies assessed through Tauc plots. Further, significant PL quenching of Gd³⁺ ions emission around 312 nm was observed with increasing PdO contents, alongside increased decay rates for the ⁶P_7/2 emitting state in Gd³⁺. An analysis of quenching constants was ultimately performed comparing results from emission intensity with the decay rates. It is suggested that a Gd³⁺ → Pd²⁺ excitation transfer and/or absorption competition lead the quenching process with a contribution from a channel depopulating the ⁶P_7/2 metastable state.