A facile two-step synthesis of an efficient narrow-band red-emitting K2NbF7:Mn4+ phosphor for warm white LEDs and its thermal quenching behavior

Mn4+-doped fluoride phosphors exhibit narrow red line emission under blue light excitation. Such phosphors can improve the color rendering index (CRI) and reduce the color temperature of white LEDs. In this study, a series of K2NbF7:Mn4+ red phosphors were successfully synthesized by a facile two-step synthesis. The structure, composition, morphology and spectral properties were studied by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and photoluminescence spectroscopy. The obtained K2NbF7:Mn4+ can emit multiple sharp emission peaks in the range of 600–650 nm under excitation of ~371 nm or ~471 nm. In particular, this phosphor has a strong zero phonon line (ZPL) emission at 620 nm and an internal quantum efficiency (IQE) ~82%. The effects of Mn4+ doping amount, hydrothermal reaction temperature and HF concentration on spectral properties were discussed and the optimal synthesis conditions were obtained. The thermal quenching behavior of K2NbF7:Mn4+ red phosphor was studied and the activated energy was determined to be 0.66 eV. The fabricated white light-emitting diode (w-LED) with a low correlated color temperature (CCT) at 3426 K and a high luminous efficiency of 134.4 lm/W was obtained by using the K2NbF7:Mn4+, which indicates that K2NbF7:Mn4+ could be a potential red component for warm w-LEDs.