Insights into the Structural, Thermal/Dilatometric, and Optical Properties of Dy³⁺-Doped Phosphate Glasses for Lighting Applications

Dysprosium-doped glasses are of interest for applications in light-emitting devices, yet the full range of effects of Dy³⁺ ions on glass properties is not fully understood. In this work, phosphate glasses with 50P₂O₅-(50 - x)BaO-xDy₂O₃ (0 ≤ x ≤ 4.0 mol %) nominal compositions were prepared by melting and the impact of Dy³⁺ ions on glass physical, structural, thermo-mechanical, and optical properties was evaluated. Following refractive index, density, and X-ray diffraction characterizations, the glasses were studied comprehensively through Raman spectroscopy, X-ray photoelectron spectroscopy, dilatometry, optical absorption, and photoluminescence (PL) spectroscopy. The thorough investigation and data analyses shed light on the Dy³⁺-driven structural and thermal properties reported here for the first time. The thermal expansion behavior was put in context with the reported data for other lanthanides and analyzed in the framework of the high ionic field strengths, leading to tighter glass networks. Further, a detailed analysis of the absorption, PL, and emission decay curves was carried out, providing insights into the origin of the optical behavior. Supported is the hypothesis that the cross-relaxation channels between Dy³⁺ ions taking place at low concentrations are responsible for the decrease in the decay times while the PL attractive for lighting applications still improves. Conversely, high Dy³⁺ concentrations facilitate the emission quenching proceeding via an electric dipole-dipole interaction likely incorporating the resonant excitation migration pathway for Dy³⁺-Dy³⁺ mean distances shorter than ∼15 Å.