High-Efficiency Mn<sup>4+</sup>-Doped Rb<sub>2</sub>GeF<sub>6</sub> Single-Crystal Phosphors: Enhanced Moisture Resistance and Performance in Warm White LEDs
Zhiyu Yang, Guangxiang Lu, Tao Yang, Xianju Zhou, Li Li, Yayun Zhou, Zhengliang Wang
Abstract
Mn 4+ -doped fluorides are renowned for their highly efficient narrow-band red emission, making them promising candidates for white light-emitting diodes and wide-gamut displays. However, performance degradation at high power levels and insufficient moisture resistance limit their application. Herein, a millimeter-sized hexagonal Rb 2 GeF 6:Mn 4+ single-crystal phosphor with superior photoluminescence quantum efficiency (QE ≈ 97%) was synthesized via a one-step saturated crystallization method. The single crystal demonstrates high stability in aqueous environments compared to its powdered counterpart, attributed to reduced hydrolysis of the [MnF 6 ] 2– group. The calculated band structure of Rb 2 GeF 6 reveals it to be a nonmagnetic, direct band gap semiconductor with a 5.89 eV band gap. A white LED device incorporating the red-emitting crystal and yellow-emitting Y 3 Al 5 O 12:Ce 3+ achieves a high color-rendering index of 84.5 at a low correlated color temperature of 2296 K, demonstrating the potential for advanced warm white LEDs. This research provides a foundation for the development of high-efficiency Mn 4+ -doped fluoride single-crystals for lighting applications.