Synthesis of a novel red phosphor K_2xBa_1-xTiF_6:Mn⁴⁺ and its enhanced luminescence performance, thermal stability and waterproofness

Investigation of efficient red phosphors is highly desired for the development of novel warm white light emitting diodes. In this paper, through a facile method, we first introduce K⁺ to replace Ba²⁺ to synthesize a novel K_2xBa_1-xTiF₆:Mn⁴⁺ solid solution phosphor with high luminous efficiency, high thermal stability and good waterproofness. Significantly, compared with two best luminescence performance samples (BaTiF₆:0.006Mn⁴⁺ and K_0.070Ba_0.965TiF₆:0.018Mn⁴⁺), the luminescence intensity of K_0.070Ba_0.965TiF₆:0.018Mn⁴⁺ is increased by 6 times, the quantum efficiency is improved from 40% to 75% and the activation energy of thermal quenching is improved to 0.940 eV from 0.628 eV. Remarkably, the waterproofness is improved by 45% than traditional red phosphor K₂TiF₆:Mn⁴⁺ after being immersed in water for 150 min. Moreover, a high-performance WLED with low correlated color temperature (CCT = 3930 K), high color rendering index (Ra = 90.3) and luminous efficacy of 105 lm/W is achieved by employing blue-emitting GaN chip, yellow-emitting YAG:Ce³⁺ phosphor and red-emitting K_0.070Ba_0.965TiF₆:Mn⁴⁺ phosphor. These results reveal that introduced suitable cation may have a positive effect on luminescent properties of Mn⁴⁺ activated fluoride phosphors, which is a helpful tool for their performance improvement, and K_0.070Ba_0.965TiF₆:Mn⁴⁺ presents a good luminescent property and may be a potential candidate for high-performance warm WLED.