My friend has transition glasses, all I know about them is they transition to dark in the sun. but how do they work? can someone please explain like im 5 years old?
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First, it isn’t a coating – the silver salts used in transition lenses are in the glass itself. This is important, because the reversibility of the reaction is really important – you want the glasses to go clear again.
Silver salts (like silver chloride) form with electrons that are a long way from the nucleus of the chlorine atom. If you hit those electrons with a high-energy UV photon, it can push an electron from the choride ion to the silver ion, which becomes a silver atom – this makes the silver atom opaque, and as more of the silver ions are hit, the glass gets progressively darker with more and more silver metal.
This happens in a solution, too – expose silver chloride solution to light, and it will change colour, because silver ions are turning to silver metal. In a solution, this reaction is not reversible, because the silver precipitates out. But the silver ions and the chloride ions in glass lenses cannot move, so they are still in the same position next to each other. Eventually the electron that was pushed to the silver ion will emit the UV energy it absorbed, and jump back to the chloride ion. Once that happens, you don’t have a silver atom any more, and the lens goes back to being clear.
There is a delicate balancing act between clear ions and silver metal, and that balancing act is determined by the Schrödinger equation, which is quantum mechanics. That part isn’t ELI5.
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