Photochromic glass

Photochromic silver—copper haUde films were produced by vacuum evaporation and deposition of a mixture of the components onto a sUicate glass substrate (13). The molar ratio of the components was approximately 9 1 (Ag Cu) and film thicknesses were in the range of 0.45—2.05 p.m. Coloration rate upon uv exposure was high but thermal fade rates were very slow when compared with standard silver haUde glass photochromic systems. 

Glass, photochromic -silver m [SILVERAND SILVER ALLOYS] (Vol 22) -silver cmpds for [SILVER COMPOUNDS] (Vol 22)... 

Photochromic dyes Photochromic glass Photochromic glasses... 

Barium carbonate Bismuth Bismuth phosphate Lanthanum oxide Tantalum oxide Zirconium potassium hexafluoride glass, photochromic Silver bromide glass, safety... 

The commercially available photochromic glasses contain a fine dispersion of silver halide crystallites which ate about 10 nm in diameter and about... 

Post-heat treatment of glass induces phase separation and crystalliza tion A very precise secondary heat treatment is necessary to develop and control photochromic properties. Glass-ceramics receive a thermal ceramming process that induces crystallization... 

Other Uses. Photochromic glass contains silver chloride (80) and silver molybdate [13765-74-7] (81) (see Chromogenic materials). An apparatus coated with silver nitrate has been described for the detection of rain or snow (82). Treatment with silver-thiosulfate complex has been reported as dramatically increasing the post-harvest life of cut carnations (83). Silver sulfate has been used in the electrolytic coloring of aluminum (84). Silver sulfate also imparts a yellowish red color to glass bulbs (85). 

Table 1. Composition of a Silver Halide Photochromic Glass ...

Thin films of photochromic glass containing silver haUde have been produced by simultaneous vacuum deposition of siUcon monoxide, lead siUcate, aluminum chloride, copper (I) chloride, and silver haUdes (9). Again, heat treatment (120°C for several hours) after vacuum deposition results in the formation of photochromic silver haUde crystaUites. Photochemical darkening and thermal fade rates are much slower than those of the standard dispersed systems. 

A typical range of glass compositions for this type of photochromic system is given in Table 2 (11). 

Simultaneous deposition of cadmium chloride and copper chloride by vacuum evaporation onto fused siUca or optical glass resulted in photochromic thin films (14). The thickness ranged from 0.25 to 1.3 pm. 

Photochromism Based on Triplet Formation. Upon absorption of light, many polycycHc aromatic hydrocarbons and their heterocycHc analogues undergo transitions to their triplet state which has an absorption spectmm different from that of the ground state (24). In rigid glasses and some plastics, the triplet state, which may absorb in the visible, has a lifetime of up to 20 seconds. 

Although the proposed appHcations for photochromic systems are numerous, few have received broad use. By far, the most successful commercial apphcation is the use of photochromic silver halide-containing glasses in prescription eyewear. The convenience of having lenses that darken automatically upon exposure to sunlight has proven appealing to spectacle wearers (35). With the increasing penetration of plastic lenses into the ophthalmic market, the desire for plastic photochromic ophthalmic lenses has also increased, and considerable effort has been spent on the discovery of photochromic systems for plastic eyewear. 

Chromogenic Materials, Photochromic" in ECT3d ed., VoL 6, pp. 121—128, by R. J. Aranjo, Corning Glass Works. 

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