Hydrothermal synthesis of narrow-band red emitting K2NaAlF6: Mn4+ phosphor for warm-white LED applications

A series of Mn4+ activated aluminofluoride (K2NaAlF6) red phosphors were synthesized via a hydrothermal route. The structure, morphology and composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). The photoluminescence properties were investigated by using emission and excitation spectra, temperature dependent luminescence spectra and decay curves. The obtained K2NaAlF6: Mn4+ can emit red light peaking at 633 nm under 460 nm excitation. The critical quenching concentration of Mn4+ was about 1%. The changes in Mn4+ emissions based on different ratios of KF to NaF, reaction temperature and reaction time were investigated in detail. Concentration and thermal quenching mechanisms were elucidated systematically. The white light-emitting diodes (WLED) fabricated with the as-prepared phosphor exhibit a low color temperature (4310 K), higher color rendering index (R-a = 78.7) and luminous efficacy of 60.22 lm W-1. The inherent advantage of K2NaAlF6: Mn4+ makes it a promising red phosphor for future WLED.