Moisture-resistant and highly efficient narrow-band red-emitting fluoride phosphor K2NaGaF6:Mn4+ for warm white LED application

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 7; no. 26; pp. 7906 - 7914
• Main Authors: Gao, Jun, Zhu, Haomiao, Li, Renfu, Huang, Decai, Luo, Benlong, You, Wenwu, Ke, Jianxi, Yi, Xiaodong, Shang, Xiaoying, Xu, Jin, Deng, Zhonghua, Xu, Li, Wang, Guo, Chen, Xueyuan
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2019
• Subjects: Color temperature; Crystal structure; Crystallography; Diodes; Emission spectra; Excitation spectra; Fluorides; Light emitting diodes; Liquid crystal displays; Luminous efficacy; Manganese ions; Moisture resistance; Phosphors; Photoluminescence; Portable document format; Relative humidity; Single crystals; X-ray diffraction
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/c9tc02445j

Mn4+-Doped fluoride red phosphors with excellent moisture-resistant properties and high emission efficiency are highly desired for warm white LEDs and wide gamut liquid crystal displays. Herein, we synthesized a K2NaGaF6:Mn4+ red phosphor through a co-precipitation method at room temperature. The crystallographic structure of the K2NaGaF6 host was determined based on single crystal X-ray diffraction data for the first time. A high internal photoluminescence quantum yield of 82% was achieved for the 1.81 at% K2NaGaF6:Mn4+ sample. Through low-temperature and high-resolution spectroscopic analysis, we revealed that Mn4+ ions occupy at least four distinct sites in the K2NaGaF6 crystal. One of them is assigned to the Ga3+ site with high Oh site symmetry and the other three ones possess low non-centrosymmetric site symmetries. By employing 5.51 at% K2NaGaF6:Mn4+ as a red phosphor, a warm white LED with a low correlated color temperature of 3760 K, a high color rendering index of 92 (Ra) and a luminous efficacy of 156 lm W−1 was packaged. Aging tests at 85 °C and 85% relative humidity on the fabricated LEDs demonstrated that K2NaGaF6:Mn4+ has a better moisture-resistant property than that of the popular K2SiF6:Mn4+ phosphor. These findings demonstrate the great potential of K2NaGaF6:Mn4+ as a highly efficient red phosphor with excellent moisture-resistant performance.