Reductant-optimized exchange strategy to construct the water-resistant shell of Mn4+-doped phosphors

Abstract

Solving the problem of poor moisture resistance of Mn4+-doped fluoride red light-emitting phosphors is the key to promoting their application in white light-emitting diodes (WLEDs). In this paper, a reductant-optimized exchange strategy is proposed, that is, treating phosphors in NH4F (40 %) solution with FeSO4 to form a Mn4+-free shell on its surface to improve the moisture resistance as well as to block energy transfer to surface defects. The thickness of the Mn4+-free shell was about 900 nm as characterized by FIB-SEM. The integrated fluorescence intensity of the treated sample (R-KTF:0.05Mn4+) was 1.07 times that of the untreated sample. The internal quantum yield (QYi) was 98 %. After testing in extreme hydrolysis environments (high temperature, high pressure, high humidity), it decreased to 93 %, which is significantly higher than the results of the in-situ passivation strategy (QYi = 28 %) and the reverse cation-exchange strategy (QYi = 37 %). Finally, aging results at 85 °C and 85 % relative humidity further confirmed that the application of this strategy resulted in a significant improvement in the operational stability of the WLEDs.