U.S. 8,133,938 B2
PPG Industries has been granted a patent for a radiation diffraction material comprised of an ordered periodic array of packed particles that diffracts radiation, the array defining interstitial spaces between particles in the array; and a polymeric matrix filled into the interstitial spaces between the packed particles, wherein the particles each comprise a core surrounded by a shell of a non-film forming composition that is different from the matrix, wherein the refractive index of the core is different from the refractive index of the shell, wherein the shell has a gradient of refractive index across the thickness of the shell, and wherein the matrix is produced from crosslinkable monomers and the monomers are present in the shell in a concentration gradient across the thickness of the shell.