Towards Improved Waterproofness of Mn4+-Activated Fluoride Phosphors
Materials Advances, 2022, 10.1039/D2MA00117A.
Abstract
The Mn 4+ -activated fluoride phosphor, typically K 2 SiF 6 :Mn 4+ , has become a renowned red-emitting phosphor for white light emitting diodes (LEDs) due to its sharp line-type luminescence spectrum peaking at 630 nm. However, the fluoride phosphors exhibit relatively poor water-resistance as the [MnF 6 ] 2– groups are prone to hydrolysis under humid condition, which leads to the formation of Mn-oxides and hydroxides causing a severe drop of luminescence efficiency. This review summarizes the six strategies that have been employed to improve the waterproofness of Mn 4+ -doped fluoride phosphors, including organic coating, inorganic heterogenerous coating, homogenerous coating, surface deactivation (reduction of surface Mn 4+ ), preparation of single crystal phosphor, and other methods (solid solution, Nb 5+ oxidation effect, structural rigidity-enhancement, etc.). The pros and cons of each strategy have been compared, and, finally, several perspectives, such as the development of single crystal phosphors with low solubility to achieve better waterproofness, have been proposed.