Analysis Of Coated-topaz Film Structure

Three generations of the coated-topaz samples in different colors were conducted in a comprehensive and systematic analysis by conventional gemological testing, X-ray photoelectron spectroscopy tests, corrosion resistance experiment, heat treatment, the conclusion was summarized as follows:The gemological character was different between coated-topaz and natural topaz. The refractive index in crown of coated-topaz are 1.619 ~ 1.627, but the refractive index in pavilion couldn't be tested; the coated-topaz under UV-fluorescence properties in both long wave and short wave was inertia as well as under cathodoluminescence instrument; the hardness in crown was 8, in pavilion was less than in crown; all of the samples do not have a multi-color; the blue coated-topaz and green coated-topaz presented light pink to pink under Charles color filter.The structure of film in coated-topaz included single layer and double layers structure and three layers structure. The khaki,honey,orange,turquoise blue,sky blue,rose red,light pink coated-topazes were single layer structure, and the rainforest,paraiba,blazing red were double structure, the pink coated-topaz was three layers structure. The thiceness of single structure film, which was less than 200nm, was thinner than the double structure film which was more than 200nm. In the same color lines, double structure coated-topazes were more colorful, take the khaki coated-topaz (which was single strcture) and the rainforest coated-topaz for example.Different film composition resulted in different colors, for instances: Ti was the cause of producing rainbow, which was TiO2; Cr,Co and Zn were the cause of producing green line, which were Cr2O3,ZnO,CoO and Co;Fe was the cause of producing honey and orange, which was Fe2O3; Co was the cause of producing blue line, which was CoO and Co in turquoise blue, was Co in sky blue and Paraiba; Au was the cause of producing red line.The root causes that the coated-topaz could present color were: the different metal ions of the film composition could produce different color, for examples, Fe3 + could produce honey and orange coated-topaz; while film thickness and the wavelength range of visible light were at the same order of magnitude, the film on the natural surface topaz could produce optical interference to make the colorless topaz colorful.