Enhanced red emission from Mn4+ activated phosphor induced by fluoride to oxyfluoride phase transformation.

Mn4+-activated (oxy)fluoride-based red phosphors have received extensive attention. In this work, a phase transformation from K 2 NbF 7 to K 3 HF 2 NbOF 5 was successfully achieved by stoichiometric control during coprecipitation process, resulting in a novel red phosphor K 3 HF 2 NbOF 5 :Mn4+ with narrow-band emission. A systematic study was carried out on its crystal structure and luminescent properties. By introducing O ions into the local coordinated structure, the emission intensity of K 3 HF 2 NbOF 5 :Mn4+ phosphors is 2.15 times as high as that of K 2 NbF 7 :Mn4+ with a photoluminescence internal quantum yield (IQE) of 73.28% and absorption efficiency (AE) of 49.68%, which could be attributed to the layered structure of the oxyfluoride host. High quenching concentration of 8.39 mol% and short decay lifetime of 4.19 ms are realized. Based on K 3 HF 2 NbOF 5 :Mn4+ and commercial YAG:Ce3+, a white light-emitting diode (WLED) for solid state lighting was fabricated, which has low CCT of 3802 K, high Ra of 86.3 and high luminous efficiency (LE) of 126.23 lm/W. Moreover, by employing commercial β-sialon:Eu2+ and K 3 HF 2 NbOF 5 :8.39%Mn4+, another WLED with high LE of 95.78 lm/W and wide color gamut of 108.6% National Television Standard Committee (NTSC) standard for backlight lighting was packaged, indicating a great potential of K 3 HF 2 NbOF 5 :Mn4+ as a red component in the application of backlight lighting. • Phase transformation from K 2 NbF 7 to K 3 HF 2 NbOF 5 was achieved by stoichiometric control. • Accompanying with fluoride to oxyfluoride phase transformation, the fluorescence intensity was greatly enhanced. • High photoluminescence quantum yield, wide color gamut and short fluorescence lifetime suit backlight applications. [ABSTRACT FROM AUTHOR]