Abstract
• The Reductant-optimized exchange strategy is proposed for surface treatment of Mn 4+ -doped fluoride phosphors. • The Mn 4+ -free shell not only improves the luminous intensity but also has the ability to resist high pressure, high pressure, and high humidity. • The quantum yield enhancement is studied by the change of the de-excitation rate. Solving the problem of poor moisture resistance of Mn 4+ -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 NH 4 F (40%) solution with FeSO 4 to form a Mn 4+ -free shell on its surface to improve the moisture resistance as well as to block energy transfer to surface defects. The thickness of the Mn 4+ -free shell was about 900 nm as characterized by FIB-SEM. The integrated fluorescence intensity of the treated sample (R-KTF:0.05Mn 4+ ) was 1.07 times that of the untreated sample. The internal quantum yield ( QY i ) 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 ( QY i =28%) and the reverse cation-exchange strategy ( QY i =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.
Published Version
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