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Sunglasses Reference Material

January 19, 2019

The color-changing lens is currently used in automobile windows, sunglasses, and visual display units, and its basic composition is halogen. Japanese researchers have developed a regenerative light-sensing lens that does not contain such environmentally harmful halogen (chlorine, bromine, and iodine) in its composition. This study has been published. In the latest issue of Chemical Communications.

Like photoreceptors, the color of today's light-sensitive lenses is deeper because of the silver and halogen compounds in the lenses, such as silver iodide. The ultraviolet light in the sunlight provides a small amount of electrons contained in the halogen ions to move, and these electrons combine with silver ions to become neutral atoms of metallic silver. These silver atoms then aggregate into tiny particles that scatter light to darken the lens.

However, the above process is reversible. Some sunglasses will return to transparency within a few minutes after being exposed to ultraviolet radiation, while others must be restored to their original state by heating. During each recovery, electrons are detached from the silver atoms, causing their metal clusters to be again separated into silver ions.

Halogen reacts with carbon-based molecules to form toxic and carcinogenic compounds. To replace halogens, Tetsuo Yazawa of the Osaka Institute of Industrial Technology (AIST) and colleagues added silver ions to silver nitrate. Completely mixed in a uniform standard lens material.

The lens made of silver nitrate turns from transparent to yellow under ultraviolet light. When the yellowed lens is heated at 500 ° C for 15 minutes, it will return to transparency. This change in the lens from transparent to yellow and restored to the original color can be repeated countless times.


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