Abstract
Near-infrared (NIR)-emitting phosphate glasses containing Nd(3+) ions are attractive for applications in laser materials and solar spectral converters. The composition-structure-property relation in this type of glass system is thus of interest from fundamental and applied perspectives. In this work, Nd(3+)-containing glasses were made by melting with 50P(2)O(5)-(50 - x)BaO-xNd(2)O(3) (x = 0, 0.5, 1.0, 2.0, 3.0, 4.0 mol %) nominal compositions and studied comprehensively by density and related physical properties, X-ray diffraction (XRD), Raman spectroscopy, O 1s X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), dilatometry, ultraviolet-visible (UV-vis)-NIR optical absorption, and photoluminescence (PL) spectroscopy with decay dynamics assessment. The densities and molar volumes of the Nd(3+)-containing glasses generally increased with Nd(2)O(3) concentration also resulting in shorter Nd(3+)-Nd(3+) distances. XRD supported the amorphous nature of the glasses, whereas the Raman spectra evolution was indicative of glass depolymerization being induced by Nd(3+) ions. Oxygen (1s) and phosphorus (2p) analysis by XPS for the glass with 4.0 mol % Nd(2)O(3) agreed with the increase in nonbridging oxygens relative to the undoped host. DSC results showed that the glass transition temperatures increased with Nd(3+) concentration, with the glasses also displaying a decreased tendency toward crystallization. Dilatometry showed trends of increasing softening temperatures and decreasing thermal expansion coefficients with increasing Nd(2)O(3) content. A glass strengthening/tightening effect was then indicated to be induced by Nd(3+) with higher field strength compared to Ba(2+) ions. The UV-vis-NIR absorption by Nd(3+) ions increased consistently with Nd(3+) concentration. The UV-vis absorption edges of the Nd-containing glasses were also analyzed via Tauc and Urbach plots for comparison with the undoped host. Concerning the PL behavior, the Nd(3+) NIR emission intensity was highest for 1.0 mol % Nd(2)O(3) and decreased thereafter. The decay kinetics of the (4)F(3/2) emitting state in Nd(3+) ions analyzed revealed decreasing lifetimes where the decay rate analysis pointed to the prevalence of ion-ion excitation migration leading to PL quenching at high Nd(3+) concentrations.