A composition including an inorganic core and a europium and yttrium oxide or gadolinium shell uniformly covering the inorganic core at a thickness greater than or equal to 300 nm is described. A phosphor including the composition is also described. In addition a process of forming the composition by: forming a suspension including the inorganic core with pH of 8 to 11; adding a solution including a europium salt and yttrium or gadolinium salt to the suspension and maintaining the pH of the reaction medium at a constant value; and separating the formed solid and calcining the same to a temperature of at most 1000° C. is described.