Synthesis and narrow red luminescence of Cs2HfF6:Mn4+, a new phosphor for warm white LEDs

Mn4+-doped fluorides show narrow red line emission under blue light excitation and are therefore promising materials to improve the color rendering and luminous efficacy of white light emitting diodes (wLEDs). The synthesis of Mn4+-doped fluorides is however challenging and so far only a few efficient Mn4+-doped fluoride phosphors have been reported. In this work we present the synthesis and optical properties of a novel Cs2HfF6:Mn4+ phosphor. The Cs2HfF6:Mn4+ phosphor is prepared via a two-step co-precipitation method and shows bright red Mn4+ luminescence around 620 nm under blue light excitation. Detailed insight in the luminescence properties is obtained by studying the Mn4+ emission and luminescence decay down to cryogenic temperatures. The Cs2HfF6:Mn4+ phosphor has a photoluminescence quantum efficiency higher than 80%, which makes it an interesting red-emitting material for wLEDs and other lighting applications. As the Mn4+ emission from Cs2HfF6:Mn4+ shows quenching above 100 degrees C (T-1/2 = 403 K), the use of this phosphor will be limited to low-power LED lighting.