Luminescence properties, crystal field and nephelauxetic effect on (NH4)2NaMF6: Mn4+ (M = Al, Ga and In) red phosphors for warm white light-emitting diodes

In recent years, M (M = Al, Ga and In)-based fluoride red phosphors have received widespread attention. Herein, the red phosphors (NH4)(2)NaAlF6:Mn4+ (NNAFM), (NH4)(2)NaGaF6:Mn4+ (NNGFM) and (NH4)(2)NaInF6:Mn4+ (NNIFM) were synthesized by hydrothermal method, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometers (EDS). Upon 470 nm light irradiation, the strongest emission peaks of (NH4)(2)NaMF6:Mn4+ red phosphors were at 637 nm (NNAFM), 636 nm (NNGFM) and 634 nm (NNIFM), respectively. This blue shift phenomenon with the increase of atomic radius was analyzed by crystal field and nephelauxetic effect. Besides, the concentration quenching mechanism, fluorescence lifetime and thermal stability were also discussed. Finally, three kinds of red phosphors were combined with blue chip and yellow phosphor (YAG:Ce3+) to form LED devices for improving their performance. The LED device (blue chip-YAG:Ce3+-NNGFM) possesses high color rendering index (Ra = 90.1), low correlated color temperature (3422 K) and luminous efficiency (41.23 lm W-1).

Automated summary

In recent years, there has been widespread interest in M (M = Al, Ga and In)-based fluoride red phosphors. In this study, three types of red phosphors were synthesized and characterized. The results showed that the emission peaks of the red phosphors were influenced by the atomic radius, and combining them with other phosphors in LED devices greatly improved their performance.