Nb-based A NbOF :Mn4+ (A=Na, Cs; x=2, 3; y=5, 6) red phosphors with excellent water resistance and enhanced luminescence by W6+/Mo6+ charge compensation

Mn4+ activated fluoride red phosphors are used in warm white light emitting diodes (WLEDs). However, their inherently low moisture resistance is a major barrier to their use in high humidity conditions. In this work, the Nb-based oxyfluoride phosphors AxNbOFy:Mn4+ (A=Na, Cs; x=2, 3; y=5, 6) were synthesized by the co-precipitation method. The crystal structure, morphology, and luminescence properties are investigated with composition variation. The non-equivalent replacement of Nd5+ ions by Mn4+ results in bright red emission under blue light excitation. These phosphors showed very good moisture resistant luminescence. The best performance was achieved by the Na3NbOF6:0.1%Mn4+, which retained 98% of the initial fluorescence intensity after immersion in water for 60 min. In addition, the W6+ and Mo6+ are used to compensate for the charge difference between Mn4+ and Nd5+ in Na3NbOF6:Mn4+. The compensated phosphors have shown large enhancements of 169% (W6+) and 168% (Mo6+) in luminescence intensity. This strategy of non-equivalent doping approach of Mn4+ into the Nb-based oxyfluoride materials and the charge compensation by W6+/Mo6+ to enhance the luminescence intensity provides a new way to realize high performance red phosphors for WLEDs.