A Graphene Quantum Dot-Coated Organic–Inorganic Hybrid Phosphor for High-Stability Narrow-Band Red Emission and Warm White LEDs

The development of Mn⁴⁺-activated fluoride red phosphors with excellent chemical stability and high luminescence efficiency for phosphor-converted white light-emitting diodes (pc-wLEDs) remains a critical challenge. In this study, a novel ethanolamine (MEA)-doped K₂TiF₆:0.1MEA,0.06Mn⁴⁺@GQDs (4 mg/mol) red phosphor was synthesized for the first time via a combined ion exchange and hydrothermal method. Comprehensive characterization confirmed the successful coating of graphene quantum dots (GQDs) on the phosphor surface. At the optimal concentration of GQDs (4 mg/mol), the material exhibited significantly enhanced luminescence properties and thermal stability compared to those of the uncoated K₂TiF₆:MEA,Mn⁴⁺ sample. The obtained organic-inorganic hybrid red phosphor displays narrow-band emission at 632 nm and a room-temperature emission intensity that is 1.52 times that of the reference sample. Moreover, it demonstrates exceptional thermal stability, maintaining a photoluminescence (PL) integrated intensity at 150 °C that is 2.64 times its initial value. These enhancements are attributed to the synergistic interaction between MEA and GQDs, which effectively suppresses Mn⁴⁺ concentration quenching and repairs lattice/surface defects. A prototype pc-wLED was fabricated by coating a mixture of this phosphor, a YAG:Ce³⁺ yellow phosphor, and an epoxy resin onto a blue InGaN chip. The device emits warm white light, with a correlated color temperature (<i>CCT</i>) of 3720 K and a color rendering index (<i>CRI</i>) of 91.2. These results indicate that the K₂TiF₆:MEA,Mn⁴⁺@GQDs phosphor provides a promising strategy for developing novel fluoride red phosphors and has potential application in warm white LEDs.