Negative thermal quenching of K3AlF6:Mn4+@GQDs phosphors caused by enhancement of the conversion of heat energy into light energy

In order to improve luminescent thermal stability, a series of new K3AlF6:0.02Mn4+@GQDs x mg/mol phosphors (graphene quantum dots: GQDs) have been synthesized with a coating strategy. Enhancement of luminescent thermal stability and emission induced by coating of GQDs are observed, which high luminescent thermal stability is caused by negative thermal quenching (NTQ). The mechanism of the NTQ is discussed and suggested as: some of thermal energy is transformed into light energy. Finally, warm white light with high color rendering index (Ra) and low correlated color temperature (CCT) is obtained from prototype white light-emitting diodes (WLEDs) using the optimal coated sample.