4 ms·

My first mystery for glass, is why is it transparent? Surely random as opposed to crystalline ordering would be better at stopping photons? Turns out it is abo

My first mystery for glass, is why is it transparent? Surely random as opposed to crystalline ordering would be better at stopping photons? Turns out it is about electron excitation levels in glass - the gaps between levels are too large to absorb the energy from a photon, so they pass right through!

kurthr 4y ago
If you're intrigued by band gaps... get some cheap synthetic Ruby (you can get a 1.5 carets for $40-50) and see what happens when it gets hot/cold. Ruby is just Sapphire (Aluminum Oxide) with Iron impurities that make it red. It is red because blue light (everything above the band gap) is absorbed! When you cool the ruby (e.g. in liquid nitrogen) it will turn pink/orange as it shrinks and the absorption band moves to shorter wavelengths. When you heat it (e.g. with a propane torch) it will turn deep red to black as the crystal structure expands and the absorption band moves up in wave length from red into the IR. Remove the heat/cold and watch it slowly come back to the ruby color you expect!
- boredemployee 4y ago
  thats a classic matter in materials science and engineering !
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marcosdumay 4y ago
You are not far from the truth. Interatomic forces tend to create energy levels with differences on the infrared band. And glass is pretty opaque on the infrared. But yes, the visible light features are usually caused by electron excitation.
Sharlin 4y ago
SiO2 glass happens to be transparent to visible wavelengths in particular, which is one of the reasons we use it. But it’s not nearly as transparent to UV and also becomes quickly opaque as you go from near IR to longer wavelengths. In "thermal" IR, glass is actually a pretty good mirror.
- failrate 4y ago
  I enjoy looking at different glasses with my polarized prescription sunglasses. They reveal all kinds of interesting distortions depending on how the glass was formed.

kurthr 4y ago

If you're intrigued by band gaps... get some cheap synthetic Ruby (you can get a 1.5 carets for $40-50) and see what happens when it gets hot/cold. Ruby is just Sapphire (Aluminum Oxide) with Iron impurities that make it red. It is red because blue light (everything above the band gap) is absorbed! When you cool the ruby (e.g. in liquid nitrogen) it will turn pink/orange as it shrinks and the absorption band moves to shorter wavelengths. When you heat it (e.g. with a propane torch) it will turn deep red to black as the crystal structure expands and the absorption band moves up in wave length from red into the IR. Remove the heat/cold and watch it slowly come back to the ruby color you expect!

boredemployee 4y ago
thats a classic matter in materials science and engineering !

deleted 4y ago

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marcosdumay 4y ago

You are not far from the truth. Interatomic forces tend to create energy levels with differences on the infrared band. And glass is pretty opaque on the infrared. But yes, the visible light features are usually caused by electron excitation.

Sharlin 4y ago

SiO2 glass happens to be transparent to visible wavelengths in particular, which is one of the reasons we use it. But it’s not nearly as transparent to UV and also becomes quickly opaque as you go from near IR to longer wavelengths. In "thermal" IR, glass is actually a pretty good mirror.

failrate 4y ago
I enjoy looking at different glasses with my polarized prescription sunglasses. They reveal all kinds of interesting distortions depending on how the glass was formed.