Use of nanoparticles to tune index of refraction of layers of a polymeric matrix to optimize microoptic (MO) focus

A security device comprising:

• one or more arrangements of image icons;
• and
• a layer of one or more arrangements of refractive image icon focusing elements, the one or more arrangements of refractive image icon focusing elements comprising a mixture of an organic resin and nanoparticles,
• wherein the one or more arrangements of refractive image icon focusing elements is disposed above the one or more arrangements of image icons such that a portion of the one or more arrangements of refractive image icon focusing elements forms a synthetic image of a portion of the one or more arrangements of image icons,
• wherein the mixture of the organic resin and nanoparticles has an index of refraction greater than 1.5, and
• wherein the nanoparticles are dispersed in the layer of the one or more arrangements of refractive image icon focusing elements and affect a geometry of the refractive image icon focusing elements.