Journal of the American Ceramic Society, Vol.103, No.12, 6901-6912, 2020
HF-free molten salt route for synthesis of highly efficient and water-resistant K2SiF6:Mn(4+)for warm white LED
It has been one of the hot issues to prepare the red-emitting Mn4+-doped fluoride phosphors with highly efficient and waterproofness for warm white-light-emitting diodes (WLEDs) by the green and environmentally friendly method. Herein, we design a novel green molten salt route to synthesize K2SiF6:Mn(4+)red powder using molten NH(4)HF(2)salt instead of HF liquor as the reaction medium. The results show that KMnO(4)and MnF(2)could produce Mn(4+)in NH(4)HF(2)molten salt through a reduction reaction, and the resulting Mn4+-doped K(2)SiF(6)exhibited a bright red emission peaked at 632 nm under blue light excitation. The luminescence intensity of the as-obtained product after immersing into water for 24 hours maintain nearly 100% of that before soaking and emission peak shape remains unchanged. The thermal stability of the sample was evaluated by temperature-dependent luminescence spectral intensity during heating and cooling. Furthermore, a warm white-light-emitting diodes (WLEDs) with an excellent color rendering index (Ra = 87.1), lower correlated color temperature (CCT = 3536K), and high luminous efficacy (116.99 lm center dot W-1) was fabricated based on blue chip and K2SiF6:Mn(4+)and commercial yellow phosphor (Y3Al5O12:Ce3+).