A Green Synthetic Route To The Narrow-Band Mn⁴⁺-Doped Fluoride Red Phosphor For Warm White Light-Emitting Diodes

White light-emitting diodes(WLEDs)are now replacing traditional lamps and being widely used in home lighting,backlights,and headlights,due to their excellent features such as energy-saving,durability and environmental friendliness.At present,the most available WLEDs are fabricated by combining a blue chip and a Y3Al5O12:Ce3+(YAG:Ce)yellow phosphor.However,the insufficient red component in the spectrum leads to a low color rendering index(CRI,Ra<80)and a high correlated color temperature(CCT>4500 K)of WLEDs,which limits its application in general illumination.To realize high performance of WLEDs,the development of red phosphors is imminent.Nowadays,the commercial red phosphors are mostly rare-earth doped nitride phosphors,such as(Sr,Ca)2Si5N8:Eu2+,(Ca,Sr)AlSiN3:Eu2+.Their rigorous synthesis conditions result in high cost.In addition,the deep red emission(>650 nm)in these phosphors is beyond the sensitivity range of the human eye,making it difficult to improve the luminous efficacy of WLEDs.Therefore,narrow red-emitting phosphors with excellent properties are continuously pursued.Recently,Mnll doped fluoride compounds are emerging as a new class of red phosphors,which may replace nitride red phosphors to fabricate high color rendering warm WLEDs.Unfortunately,in the synthesis of such phosphors,almost all methods inevitably use HF solutions.Therefor,when considering safety and environmental concerns,a HF-free green method is highly required to synthesize fluoride phosphors.Based on the above background,we propose a green method to prepare Mn4+doped fluoride phosphors.This method leads to both high efficiency and low thermal quenching of the phosphor.Moreover,the reaction principle of this method is explored.The WLEDs using the as-synthesized phosphors have a great proformance,indicating that phosphors synthesized by the proposed method has potential for the use in WLEDs.