Colored coatings on eye glass lenses by noble metal colloids

Abstract

Metal colloids in glass coatings are suitable for preparation of colored transparent coatings with thicknesses of about 0.2 to 1 µm due to their high molar coefficient of absorbance (approximate to 10(6) 1/(mol cm)). The absorbance of these metallic particles in a dielectric environment is caused by a surface plasmon resonance effect of the conductive electrons of the colloids. Therefore, it is characteristic for the metal, but can be affected by the dielectric properties of the surrounding matrix. Glass sol-gel coatings have been developed for the preparation of 0.2 to 0.4 µm thick, transparent colored coatings on silicate eye glass lenses by incorporation of Au-, Ag- and Pd-colloids into an 87 mol% SiO2-13 mol% PbO glass. A functionalized silane has been used as a complex forming agent for the appropriate noble metal ions to control the nucleation and growth processes of the colloids during the thermal densification of the coatings. By mixing different noble metal salts and addition of Co2+ ions, pink, brown, green and grey colors with optical densities less than or equal to 6 have been obtained. By variation of the glass composition the refractive index of the coating can be adapted to that of different types of substrate glasses (n(D) from 1.52 to 1.6) to obtain coatings with desirable optical performance. In a similar manner the transformation temperature (T-g) of the coatings can be less than the substrate, allowing a complete thermal densification of the coatings at about 500 degrees C. The coatings show glass like chemical durability and mechanical stability. Due to the optical and thermomechanical properties of the colored coatings and due to the thermal and UV-stability of the colloids these coatings were applied to eye glass lenses.