A novel Mn4+-activated fluoride red phosphor Cs30(Nb2O2F9)9(OH)3·H2O:Mn4+ with good waterproof stability for WLEDs

Abstract

Red-light-emitting materials, as pivotal components of warm white light-emitting diodes (WLEDs), have drawn increasing public focus. Among these, Mn⁴⁺-doped red light-emitting fluorides have drawn considerable attention when combined with an InGaN chip; however, they suffer from poor water stability under humid conditions. In this work, a novel fluoride red phosphor, Cs₃₀(Nb₂O₂F₉)₉(OH)₃·H₂O:xMn⁴⁺ (CNOFM), with good water resistance was synthesized for the first time using a facile co-precipitation method at ambient temperature. Experiments were implemented for the precise analysis of its crystal structure, optical properties, micro-morphology, thermal behavior, and waterproof properties. 6.66% Mn⁴⁺-doped CNOFM maintained a stable crystal structure and possessed strong PL intensity located at 633 nm with high color purity of 96%. CNOFM showed better thermal and waterproof stability compared with the commercial K₂SiF₆:Mn⁴⁺ red phosphor. Without any surface modifications, the PL intensity remained at about 83% of the initial value after immersion in water for 60 min, and the mechanism was investigated. Finally, a warm WLED with a CRI of 92.3 and CCT of 3271 K was fabricated using the CNOFM red phosphor.