Patent ID: 6841092

Claim:
A composition capable of anti-Stokes fluorescence, wherein the wavelength of the emitted electromagnetic radiation is shorter than the wavelength of the absorbed electromagnetic radiation, comprising: (a) an ytterbium ion capable of absorbing the electromagnetic radiation; (b) an ion capable of emitting the electromagnetic radiation; and (c) a matrix composition comprising an oxysulfide of the formula (R 1-x-y ) 2 O 2 S:Yb x A y ; wherein the concentrations of ytterbium ions and ions capable of emitting the electromagnetic radiation are adjusted to achieve concentration quenching of anti-Stokes luminescence; wherein R is selected from gadolinium, yttrium, lanthanum, and lutetium; wherein 0.20≦x≦0.60 and 0.0001≦y≦0.05; and wherein A is the ion capable of emitting the electromagnetic radiation.