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

Abstract

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 6P7/2 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.