Ive been collecting gems for 10+ yrs, rubies are a favorite, I have been told the glow from Burmese rubies is due not only from the low iron content but the chrome content as well, I thought the chrome added to the color, rich red, & the glow was from low Fe content. I heard a few gem sellers that Mozambique rubies will not glow under UV, I have stones that show as well as the burmese material or better, these were verified as non-burma stones. Some of the 'new find' Mozambique material will fluoresce as good or better than burmese & is cleaner in larger stones. My question is, is the iron content in rubies the controlling factor in the ruby 'glow'? Thanks to all-
Both chromium and iron are controlling factors, in opposite ways:
The fluorescence in ruby comes from chromium absorbing part of the UV spectrum and emitting visible light at 694 nm (red). Iron, on the other hand, quenches fluorescence.
Ideally, to have a very strong fluorescence, you need a high chrome content and no iron (or as little as possible).
As Dioptase says, the more chromium impurity in a ruby, the more it fluoresces. And then iron dampens out the fluorescence.
The chromium in ruby converts not only UV light to red fluorescence, it also converts visible light from violet to yellow into red fluorescence. So ruby is "glowing" even in visible light.
You can, for example, shine a blue or green LED light on ruby, and the ruby will still look red. Whereas if you shine only blue light on a red garnet, it will just look black.
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