Spectral characteristics of highly thermally stable Eu3+-doped P2O5-B2O3-ZnO-BaO glasses for tricolor WLEDs and red lasers

In this study, Eu ³⁺doped P ₂O ₅-B ₂O ₃-ZnO-BaO (PBZB) glasses were synthesized using the melt-quenching method. Phonon sideband analysis enables the determination of the glasses` phonon energy at 1212 cm <sup>−1</sup>, which agrees with the data derived from the FTIR spectrum. Under excitation at 393 nm, the PBZB glasses all exhibit a high-purity red emission with a color purity nearly 100 % and a correlated color temperature below 4000 K, as well as their chromaticity coordinates close roughly to those of standard red light (0.67, 0.33). Optimal red emission is achieved in the PBZB glasses with a Eu <sub>2</sub>O <sub>3</sub> concentration of 2.0 mol%. The luminescence lifetimes of Eu <sup>3+</sup> ions, being in the millisecond range, exhibit an initial increase followed by a decrease. Based on the Inokuti-Hirayama model, the energy transfer process among Eu <sup>3+</sup> ions is primarily driven by the d-d interactions and occurs predominantly within the clusters of the Eu <sup>3+</sup>-Eu <sup>3+</sup> ions. Further substantiation of the high covalency and asymmetry of the Eu <sup>3+</sup>-O <sup>2−</sup> bonds is supported by the Judd-Ofelt theory calculations. The glass doped with 2.0 mol% Eu <sub>2</sub>O <sub>3</sub> demonstrates an enhanced branching ratio, emission cross-section, gain bandwidth, and optical gain, confirming its potential for applications in high-gain lasers. Temperature-dependent emission spectra reveal the PBZB glasses` excellent thermal and chromaticity stability across 298–473 K. At 150 °C, the emission intensity at 612 nm for the 2.0 mol% Eu ₂O ₃-doped PBZB glass maintains 72 % of its initial value, with a chromaticity shift of only 4.36 × 10 ⁻³, substantially below the criteria of 0.015. Consequently, this study confirms the significant potential of 2.0 mol% Eu ₂O ₃-doped PBZB glass for applications in tricolor WLEDs and red lasers.