Enhancement of the luminescent thermal stability and water resistance of K2SiF6:Mn4+,Na+ by double coating of GQDs and K2SiF6

Abstract

Nowadays, it is still a big challenge to synthesize Mn4+-doped fluoride red phosphors with high water resistance, luminescent intensity and thermal stability simultaneously. Therefore, KSF:M,N@GQDs@KSF (K2SiF6:0.06Mn,0.10Na@GQDs (12 mg/mol)@K2SiF6(0.2 wt), KSF: K2SiF6, GQDS: OH-contained graphene quantum dots) with high luminescent intensity, high luminescent thermal stability and water resistance have been synthesized via a combination of H2O2-free room temperature reaction method, hydrothermal coating method and room temperature surface coating process. Experimental results show that enhancement of negative thermal quenching (NTQ) effect and water resistance can be synergistically induced by double coating of GQDs and KSF. After being immersed in deionized water for 360 min, emission intensities of the KSF:M,N@GQDs and KSF:M,N@GQDs@KSF are decreased from 100% to 70.57% and 91.63%, respectively, indicating that water resistance of the latter is obviously improved by coating of KSF. The improved water resistance is attributed to preventing hydrolysis of [MnF6]2- on sample’s surface by insoluble coating shell of KSF. A prototype WLEDs (white light-emitting diodes) emitted warm white light (CCT = 4546 K and Ra = 91.3, at a driving current of 20 mA) has been assembled by coating mixture of KSF:M,N@GQDs@KSF, yellow emitting phosphor (YAG:Ce3+) and epoxy resin on blue light InGaN chips. The good performances of the WLEDs suggest that the KSF:M,N@GQDs@KSF has potential applications in blue-based warm WLEDs.