Surface modification of K 2 TiF 6 :Mn 4+ phosphor with SrF 2 coating to enhance water resistance

K 2 TiF 6 :Mn 4+ 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 K 2 TiF 6 :Mn 4+ phosphor with SrF 2 coating has been introduced, with the aid of KHF 2 transition layer to moderate the lattice mismatch. The reaction mechanism is discussed in detail, as so as the influence of SrF 2 coating on the luminescence intensity. The SrF 2 coating is able to prevent the hydrolysis of internal [MnF 6 ] 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 Y 3 Al 5 O 12 :Ce 3+ and as‐modified K 2 TiF 6 :Mn 4+ 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 Mn 4+ doped fluoride phosphors for commercial application in the field of white LEDs.