Surface modification of K2TiF6:Mn4+ phosphor with SrF2 coating to enhance water resistance

K2TiF6:Mn4+ is an attractive narrow‐band red‐emitting phosphor for warm white light‐emitting diodes (LEDs). Nevertheless, the hexafluoride phosphor is liable to deliquesce in moist environments, which leads to a sharp deterioration performance of luminescence. Surface modification of K2TiF6:Mn4+ phosphor with SrF2 coating has been introduced, with the aid of KHF2 transition layer to moderate the lattice mismatch. The reaction mechanism is discussed in detail, as so as the influence of SrF2 coating on the luminescence intensity. The SrF2 coating is able to prevent the hydrolysis of internal [MnF6]2− group; thereby, the luminescence intensity retains over 90% of initial value after being immersed in distilled water for 2 h. The LED devices fabricated with commercial Y3Al5O12:Ce3+ and as‐modified K2TiF6:Mn4+ phosphors exhibit bright white light with tunable chromaticity coordinate, correlated color temperature, and color rendering index. It enlightens a convenient method to enhance the moisture resistance of Mn4+ doped fluoride phosphors for commercial application in the field of white LEDs.