Structure-property inquiry of UV-emitting Gd³⁺-activated phosphate glasses

Phosphate glasses containing Gd³⁺ ions as ultraviolet (UV) type B light emitters are of interest for applications in phototherapy lamps for treating skin diseases. The composition-structure-property relation in this type of glass systems is thus of interest from fundamental and applied perspectives. In this work, Gd³⁺-containing glasses were prepared by melting with 50P₂O₅-(50 – x)BaO-xGd₂O₃ (x = 0, 1, 2, 3, 4, 5 mol %) nominal compositions, and studied comprehensively by X-ray diffraction (XRD), densitometry, Raman spectroscopy, differential scanning calorimetry (DSC), dilatometry, optical absorption, and photoluminescence (PL) spectroscopy with emission dynamics appraisal. XRD supported the amorphous nature of the glasses, whereas the densities of the Gd³⁺-containing glasses were found to increase with Gd₂O₃ content. The Raman spectra evolution was indicative of glass depolymerization being induced by Gd³⁺ ions. DSC results showed that the glass transition temperatures increased with Gd³⁺ concentration while the glasses exhibited decreased susceptibility for crystallization. Dilatometry ultimately revealed a steady decrease in the coefficient of thermal expansion for the Gd³⁺-containing glasses indicating tighter networks were realized. The PL evaluation showed that the UVB emission intensity at 312 nm increased linearly with Gd³⁺ concentration, even though the ⁶P_7/2 state lifetime reached a maximum for 2 mol % Gd₂O₃. The PL intensities finally showed strong linear correlations with the thermal parameters linked to the structural evolution thus supporting the interconnection between the properties.