Red-emitting Mn 4+ -doped CaAl 4 O 7 phosphors for applications in high color rendering index warm white light-emitting diodes and plant growth LEDs responsive to red phytochrome and all of chlorophyll

Abstract In this study, red-emitting Mn 4+ -activated CaAl 4 O 7 phosphors were successfully synthesized using a simple solid-state reaction method. The incorporation of Mn 4+ ions into the CaAl 4 O 7 lattice was confirmed by x-ray diffraction (XRD) analysis. The synthesized phosphors displayed a red emission band peaking at 656 nm, which can be tuned by adjusting the doping concentration and annealing temperature. The highest photoluminescence intensity was observed for the CaAl 4 O 7 :0.3%Mn 4+ sample annealed at 1500 °C. The optimized CaAl₄O₇:Mn 4+ phosphors exhibited a long lifetime of 0.827 ms, good color purity of 99.5% and high quantum efficiency of 49.7%. The plant growth LEDs were fabricated by combining the red-emitting optimized CaAl 4 O 7 :Mn 4+ phosphor with various LED chips emitting at 365, 395, 420, and 450 nm. The red phytochrome exhibits good alignment with the LED chips using UV and NUV excitation (around 365 nm and 395 nm), while chlorophyll A and B show strong correspondence with plant LED chips based on the violet (420 nm) and blue (450 nm) LED chips, respectively. Furthermore, high CRI warm white light-emitting diodes (W-WLEDs) were fabricated using the red-emitting CaAl 4 O 7 :Mn 4+ phosphor with a commercial yellow YAG:Ce 3+ and a 465 nm blue LED chip. Adding CaAl 4 O 7 :Mn 4+ significantly enhanced the CRI from 77 to 91, improved the R9 value from −15 to 84, and reduced the correlated color temperature from 5581 to 3998 K. The results indicate the significant potential of CaAl 4 O 7 :Mn 4+ phosphor for applications in both high CRI W-WLEDs and plant growth LEDs, effectively responding to red phytochrome and all chlorophyll absorption bands.