Optimization of the luminescence efficiency and moisture stability of a red phosphor KRb3Ge2F12:Mn4+ for indoor plant growth LED applications

Owing to the ease of synthesis and the unique luminescence characteristics for the applications of white light emitting diodes (WLEDs), the red-emitting fluoride phosphors activated by Mn4+ ions are critical to achieving WLEDs with ideal color rendering index (CRI). In this work, a new type of Mn4+ doped phosphor KRb3Ge2F12:Mn4+ (KRGF:Mn) has been synthesized by a simple ion-exchange method in atmosphere. A strategy of surface modification by using a weak reducing agent oxalic acid (OA) is proposed, which can essentially improve the moisture stability of phosphor KRGF:Mn. Moreover, the modified phosphors can still maintain bright red light after being completely immersed in water for more than 100 days. A group of LEDs combined with the as-synthesized phosphor KRGF:Mn as a light source can be well applied to artificial lighting for the growth of tomatoes and Chinese cabbage plants. Additionally, the luminescence efficiency of KRGF:Mn has been optimized with high thermal stability. This work will provide high-quality red phosphor for LED lighting sources that being required for indoor plant growth.