Enhancement of the luminescent thermal stability and water resistance of K2TiF6:Mn4+ by organic inorganic hybrid matrix and surface passivation

Abstract

Due to their attractive luminescent properties, Mn4+-activated fluoride red-emitting phosphors are significant for improving correlated color temperature (CCT) and color rendering index (Ra) of white light-emitting diodes (WLEDs). However, the inherent poor moisture resistance of these phosphors limits their further application in WLEDs. Herein, KTF:TEAH+,Mn4+-P (KTF:TEAH+,Mn4+ = K2TiF6:0.10(C2H5)3NH+,0.04Mn4+, P = passivation with citric acid solution) red emitting phosphor with good water resistance, high luminous intensity and good luminescent thermal stability was generated by combining ion exchange and surface passivation method. The experimental results show that: (a) Emission intensities of samples are improved by using an organic-inorganic hybrid matrix and surface passivation; (b) Water resistances of samples are greatly increased by surface passivation; (c) Negative thermal quenching (NTQ) effect of the samples are enhanced by using an organic-inorganic hybrid matrix and surface passivation. The reason for improvement of water resistance is assigned to the formation of a Mn4+ -rare protective layer on the surface of the sample after surface passivation. Furthermore, the mechanism of the strong NTQ effect is attributed to the increase of electron traps by using an organic-inorganic hybrid matrix and surface passivation. A WLED prototype capable of emitting warm white light (luminous efficiency = 108.6 lm/W, CCT = 3725 K, Ra = 88.4) was assembled by coating a mixture of KTF:TEAH+,Mn4+-P, epoxy resin and YAG:Ce3+ on a blue InGaN chip. These excellent properties indicate that the KTF:TEAH+,Mn4+-P has important application value in blue-excited WLEDs.