Photosensitive glass is a crystal-clear glass that belongs to the lithium-silicate family of glasses, in which an image of a mask can be captured by microscopic metallic particles in the glass when it is exposed to short wave radiations such as ultraviolet light. Photosensitive glass was first discovered by S. Donald Stookey in 1937
Photosensitive glass was invented in November 1937 by Dr. Donald Stookey of the Corning Glass Works. It was not announced publicly until ten years later on June 1, 1947. It was officially patented in 1950 by Stookey as U.S. Pat. No. 2,515,937 and U.S. Pat. Nos. 2,515,943 with gold microscopic particles.
When the glass is exposed to UV light in the wavelength range 280–320 nm, a latent image is formed. The glass remains transparent at this stage, but its absorption in the uv range of the spectrum increases. This increased absorption is only detectable using uv transmission spectroscopy. The reason behind this is suggested to be an oxidation reduction reaction that occurs inside the glass during exposure in which cerium ions are oxidized to a more stable state and silver ions are reduced to silver.
When the glass is heated to temperatures in the range 550–560 °C for several hours the latent image is converted to a visible image through photoexcitation. Exposure through photographic negatives permits the development of three-dimensional color images and photographs. This heat treatment is done in two stages: the temperature is first raised to about 500 °C to allow for the completion of the oxidation-reduction reaction, and formation of silver nanoclusters. In the following stage, when the temperature is raised to 550–560 °C, a new material (lithium metasilicate) with the formula (Li2SiO3) forms on the silver nanoclustors, this material forms in the crystalline phase.
The lithium metasilicate that forms in the exposed regions of the glass has the unique property of being strongly etched in hydrofluoric Acid (HF). Hence allowing a three-dimensional image of the mask to be produced, the resulting glass microstructures have a surface roughness in the range 5 μm to 0.7 μm.
As stated above radiation produces some direct and indirect measurable changes in the glasses. In some cases, the effect is readily observable immediately upon irradiation. In other cases, thermal treatment is required to bring about the observed changes. On the whole, the result of the mentioned reactions will be atomic silvers and/or silver clusters which act as nucleant for precipitation of lithium-meta-silicate during post heat-treatment of irradiated glass and Similar to other glass-ceramic systems, the more nucleation sites leads to more reduction of crystallization temperature and finer crystalline size. Therefore, to attain the above-mentioned condition, various energetic radiation such as UVand laser beam and x γ and proton and radiations have been used for different photosensitive glasses until now. Imanieh et al. investigated the effect of X-ray irradiation on solarization of photosensitive lithium silicate based glasses containing cerium, antimony, tin and silver elements. They have shown that there is a possibility to use X-ray in photosensitive glasses. This will open new doors for nano machining of glasses in near future.