Physical, Thermal, and Optical Properties of Mn²⁺ and Nd³⁺ Containing Barium Phosphate Glasses

This work reports on various properties and analysis of optical interactions in phosphate glasses containing red-emitting Mn²⁺ and near-infrared (NIR)-emitting Nd³⁺ ions, which are of interest for energy applications and solar spectral converters. The glasses were made by melting with 50P₂O₅-(48 - x)BaO-2MnO-xNd₂O₃ (x = 0, 0.5, 1.0, and 2.0 mol %) nominal compositions and characterized by X-ray diffraction, density and related physical properties, differential scanning calorimetry, dilatometry, UV-vis-NIR optical absorption, and photoluminescence spectroscopy with decay kinetics analysis. The glasses were X-ray amorphous, wherein the physical and thermal properties of the Mn²⁺/Nd³⁺-codoped glasses were largely impacted by Nd₂O₃ contents. The optical absorption spectra supported the occurrence of Mn²⁺ ions and the lack of Mn³⁺ in the codoped glasses, while the absorption due to Nd³⁺ ions increased steadily with Nd₂O₃ contents. Analyzing the glass absorption edges via Tauc and Urbach plots was further pursued for a comparison. The photoluminescence evaluation showed a consistent suppression of the emission from Mn²⁺ ions with increasing Nd³⁺ concentration, while the decay kinetics revealed shorter lifetimes in connection with increased Mn²⁺ → Nd³⁺ transfer efficiencies. Excitation of Mn²⁺ at 410 nm, however, led to the Nd³⁺ NIR emission being most intense for 1.0 mol % Nd₂O₃, despite the ⁴F_3/2 emission decay analysis showing lifetime shortening throughout. Considering the compromise between red and NIR emissions, the Mn-containing glass doped with 0.5 mol % Nd₂O₃ is put in perspective with the concept of solar spectral conversion.