Analysis of thermal chromaticity stability, energy transfer and colour tunablity of Dy³⁺-Eu³⁺ doped BBZL glasses for high-power W-LED applications

A family of highly thermal chromatic stable Dy³⁺-Eu³⁺ doped B₂O₃-Bi₂O₃-ZnO-Li₂O (BBZL) glass samples was synthesised using the high-temperature melt quenching technique. The optical and thermal stability properties of the samples were analysed using their fluorescence spectra at various temperatures, fluorescence lifetime decay times and colour coordinates. The Dy³⁺-doped BBZL (BBZL: Dy) glass samples generated cold white light when exposed to ultraviolet (UV) light, while the Dy³⁺-Eu³⁺-doped BBZL (BBZL: DyEu) glass samples emitted neutral and warm white light, which can be attributed to the introduction of Eu³⁺ that substantially enhanced the colour rendering of samples. An overlap of the excitation-emission spectra of Eu³⁺ and Dy³⁺ indicated an energy transfer between Dy³⁺ and Eu³⁺. Under a 350 nm excitation, the fluorescence lifetime of BBZL: DyEu decreased from 0.5348 to 0.3642 ms. Using the Dexter theory, the energy transfer between Dy³⁺ and Eu³⁺ was demonstrated to be an electric dipole-electric dipole leap. The chromaticity shifts of BBZL: DyEu were 8.60 × 10⁻⁴ and 9.40 × 10⁻⁴ at 448 and 498 K, respectively, reflecting the high thermal stability of the sample chromaticity. The study demonstrated that Dy³⁺-Eu³⁺ doped borate glasses can be used as tunable luminescent materials in high-power white light-emitting diodes to mitigate the chromaticity shift in fluorescent materials at high temperatures.