Security element

A security device comprising:

• a medium, or a substrate having a low index of refraction nlow;
• a waveguiding layer having a high index of refraction nhigh and comprising a luminescent material;
• and
• a diffractive microstructure on a surface of the waveguiding layer, at an interface between the medium or the substrate and the waveguiding layer, or at a distance smaller than 500 nm from the waveguiding layer,
• wherein
• a refractive index difference between the medium or the substrate and the waveguiding layer is at least 0.005;
• a microstructure period is from 100 to 1500 nm;
• a mass thickness of the waveguiding layer is from 30 to 1000 nm;
• and
• a microstructure depth is from 50 to 1000 nm,
• wherein the waveguiding layer further comprises a matrix material and said matrix material is selected from the group consisting of a polyvinylcarbazole, a polymethylmethacrylate, a UV primer, a vinyl chloride copolymer, a vinyl acetate copolymer, and a nitrocellulose;
• wherein the luminescent material is at least one selected from the group consisting of a metal complex, a fluorescent organic dye, a fluorescent polymer, and a substituted phthalimidine dye;
• and
• wherein
• the metal complex is at least one selected from the group consisting of
• the fluorescent organic dye is
• the fluorescent polymer is
• wherein x is 0.90 and y is 0.10;
• and the substituted phthalimidine dye is