High water resistance and luminescent thermal stability of organic-inorganic hybrid K2SiF6:Mn4+ red emitting phosphor induced by a multi-dentate ligand

Mn4+-activated fluoride is a kind of high-efficiency red-emitting phosphor widely used in WLEDs (white light-emitting diodes). However, the poor moisture resistance hampers their commercial application on a large scale. Here, a new type of organic-inorganic hybrid KSF:HMTA, Mn4+ (KSF:K2SiF6, HMTA: hexamethylenetetramine) red-emitting phosphor has been prepared through the cation exchange method. Compared with KSF:0.04Mn4+, emission intensity, florescent thermal stability, and water resistance of KSF:HMTA,0.04Mn4+ are improved significantly due to the formation of MOF (metal-organic framework) between HMTA and K2MnF6. MOF creates an antenna effect and forms an insoluble protective shell on the sample surface. The former induces the negative thermal quenching (NTQ) effect via phonon-excited electron interaction, significantly improving the florescent thermal stability. The latter prevents the contact of Mn4+ ions on the sample surface with water molecules, resulting in enhancement of waterproofness. The formation mechanism of the MOF was discussed. A prototype WLED with warm white light (CCT = 3815 K and Ra = 90.4) were assembled via coating a mixture of YAG:Ce3+, KSF:HMTA,0.04Mn4+ and epoxy resin on a blue-emitting chip (450 nm). The results show that KSF:HMTA, 0.04Mn4+ is a potential red-emitting phosphor that can be used on its part of WLEDs.