Luminescent characteristics of Tm ³⁺/Tb ³⁺/Eu ³⁺ tri-doped Na ₅Y ₉F ₃₂ single crystals for white emission with high thermal stability

By using an improved Bridgman method, 0.3 mol% Tm ³⁺/0.6 mol% Tb ³⁺/ y mol% Eu ³⁺ ( y = 0, 0.4, 0.6, 0.8) doped Na ₅Y ₉F ₃₂ single crystals were prepared. The x-ray diffraction, excitation spectra, emission spectra and fluorescence decay curves were used to explore the crystal structure and optical performance of the obtained samples. When excited by 362 nm light, the cool white emission was realized by Na ₅Y ₉F ₃₂ single crystal triply-doped with 0.3 mol% Tm ³⁺/0.6 mol% Tb ³⁺/0.8 mol% Eu ³⁺, in which the Commission Internationale de l’Eclairage (CIE) chromaticity coordinate was (0.2995, 0.3298) and the correlated color temperature (CCT) was 6586 K. The integrated normalized emission intensity of the tri-doped single crystal at 448 K could keep 62% of that at 298 K. The internal quantum yield (QY) was calculated to be ∼ 15.16% by integrating spheres. These results suggested that the single crystals tri-doped with Tm ³⁺, Tb ³⁺ and Eu ³⁺ ions have a promising potential application for white light-emitting diodes (w-LEDs).