Moisture-resistant and highly efficient narrow-band red-emitting fluoride phosphor K 2 NaGaF 6 :Mn 4+ 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, Guo, Wang, Chen, Xueyuan
• Format: Journal Article
• Language: English
• Published: 04.07.2019
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/C9TC02445J

Mn 4+ -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 K 2 NaGaF 6 :Mn 4+ red phosphor through a co-precipitation method at room temperature. The crystallographic structure of the K 2 NaGaF 6 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% K 2 NaGaF 6 :Mn 4+ sample. Through low-temperature and high-resolution spectroscopic analysis, we revealed that Mn 4+ ions occupy at least four distinct sites in the K 2 NaGaF 6 crystal. One of them is assigned to the Ga 3+ site with high O h site symmetry and the other three ones possess low non-centrosymmetric site symmetries. By employing 5.51 at% K 2 NaGaF 6 :Mn 4+ as a red phosphor, a warm white LED with a low correlated color temperature of 3760 K, a high color rendering index of 92 ( R a ) 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 K 2 NaGaF 6 :Mn 4+ has a better moisture-resistant property than that of the popular K 2 SiF 6 :Mn 4+ phosphor. These findings demonstrate the great potential of K 2 NaGaF 6 :Mn 4+ as a highly efficient red phosphor with excellent moisture-resistant performance.