Composition-dependent scintillation properties of Ce3+-Doped KGd(PO3)4 glasses

KGd(PO₃)₄ (KGP) glasses doped with 3.0 mol% Ce³⁺ and systematically varied K₂O:Gd₂O₃ ratios were prepared by the melt-quenching method and exhibit pronounced composition-dependent optical and scintillation properties. FTIR analysis revealed progressive network depolymerization with increasing K₂O content, as evidenced by an increase in the average number of non-bridging oxides from 1.41 to 1.64. In the transmission spectra, the Ce³⁺ 4f–5d absorption band was observed in all samples, and the band exhibited a pronounced wavelength shift depending on the compositional ratio. When the composition deviated from the stoichiometric KGP (becoming either Gd-rich or K-rich), the absorption and photoluminescence (PL) band red-shifted in both cases: in the Gd-rich samples due to crystal-field strengthening associated with reinforcement of the phosphate network, and in the K-rich samples due to the nephelauxetic effect arising from increased optical basicity, both of which induce a low-energy shift of the Ce³⁺ 5d level. The absolute PL quantum yield (QY) peaks at 81.1 % for stoichiometric KGP and decreases sharply with off-stoichiometric deviation; at the same time, the PL decay time constant shortens, indicating increased nonradiative loss and a reduced radiative fraction in the off-stoichiometric glasses. The integrated photoacoustic (PA) intensity is minimal at the stoichiometric KGP sample and increases toward both extremes; the scintillation light yield (LY) is anti-correlated with PA intensity and positively correlated with PL QY. Under γ-ray excitation, the stoichiometric KGP sample exhibits the maximum LY (∼2860 photons/MeV) and a low afterglow (∼2.08 × 10¹ ppm), lower than Tl:CsI (1.09 × 10² ppm). These results indicate that changes in glass structure due to adjustments in K₂O:Gd₂O₃ significantly affect scintillation performance.