Coated phosphor particles with refractive index adaption

Coated phosphor particles comprising:

• luminescent particles and at least one coating of at least one metal, transition-metal or semimetal oxide, wherein said coating contains at least two components of different refractive index, wherein the coating has a refractive-index gradient from inside to outside, with the higher refractive index being on the inside and the lower refractive index being on the outside, wherein the surface of the coated phosphor particles is porous,
• said refractive-index gradient being formed by a composition gradient within said coating wherein the component of said at least two components having the higher refractive index essentially forms a first surface of the coating, adjacent the surface of each of said particles, and the component of said at least two components having the lower refractive index essentially forms a second surface which is the outside surface of said coating, and in between said first and second surfaces there is a mixture of the at least two components, with said mixture exhibiting a composition gradient.