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;
• one or more arrangements of refractive image icon focusing elements;
• and
• a sealing layer,
• 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 projects a synthetic image of a portion of the one or more arrangements of image icons,
• wherein the one or more arrangements of refractive image icon focusing elements contact the sealing layer,
• wherein at least one of the one or more arrangements of refractive image icon focusing elements and the sealing layer comprises an organic resin mixture including metallic nanoparticles and a first refractive index, and
• wherein at least one of the arrangements of refractive image icon focusing elements and/or the sealing layer comprises a low-refractive index material, the low-refractive index material having a second refractive index,
• wherein a relative value between the first refractive index and the second refractive index affects a geometry of at least one of the one or more arrangements of refractive image icon focusing elements.