A narrow-band red-emitting K2LiGaF6:Mn4+ phosphor with octahedral morphology: Luminescent properties, growth mechanisms, and applications

Highlights: • The K₂LiGaF₆:Mn⁴⁺ Octahedra and microsphere samples were prepared and the growth mechanisms were investigated. • The slight shift in peak position of K₂LiGaF₆:Mn⁴⁺ than K₂LiAlF₆:Mn⁴⁺ was analyzed. • The WLED that combined with YAG:Ce and K₂LiGaF₆:Mn⁴⁺ phosphors shows excellent warm white light. A narrow-band K₂LiGaF₆:Mn⁴⁺ red phosphor with octahedra and self-assembled microspheres morphologies was prepared through the two-step co-precipitation and hydrothermal methods, respectively. The forming mechanism of the regular octahedral crystals and self-assembled microspheres have been explored by SEM and HRTEM. The Mn⁴⁺ doping concentration and reaction time were optimized for improving its optical properties. The emission intensity of K₂LiGaF₆:Mn⁴⁺ can still keep 87% when it worked at 150 °C, indicating its excellent thermal stability. Moreover, the as-prepared K₂LiGaF₆:Mn⁴⁺ have better photoluminescence intensity and thermal stability than the previously reported K₂LiAlF₆:Mn⁴⁺, which should be attributed the optimization of morphology and structure. Especially, the slight shift of peak position of K₂LiGaF₆:Mn⁴⁺ than K₂LiAlF₆:Mn⁴⁺ was also analyzed in detail. Finally, the as-prepared K₂LiGaF₆:Mn⁴⁺ phosphor was packaged on WLED through combining the YAG:Ce phosphor. Excellent warm white light with the CCT = 4296 K, R_a = 91, and luminous efficiency = 137.56 lm·W⁻¹ was obtained, making it becoming the promising red phosphor candidates for white light-emitting diodes.