Patent ID: 7288150

Claim:
Method of preparing a phosphor comprising the step of growing its surface by firing or evaporating as components composing the said phosphor, a matrix component and a dopant activator element, wherein growing said phosphor, during a last incremental growth before ending said growth, proceeds over a distance q, expressed in μm, in its largest direction, provided that an increase of the said phosphor in volume, expressed in volume percentage, is more than 5%; characterized in that an activator element partition, determined before and after growth of a surface layer of said phosphor over a distance corresponding with q/10 satisfies the condition: −( q/ 10) −1 <rico<0 wherein said “rico” value, expressed in μm −1 , is calculated as a ratio of concentration differences of said activator concentration (1), determined at a depth of q/10 under said surface and said activator concentration (2) determined at said surface, and said activator concentration (2) determined at said surface, divided by the product of 0.1 times q.