I think I understand how a solid can appear transparent as long as the energy of the photons travelling through it are not absorbed in the material's bandgap. But how does this band gap relate to conduction and valence bands which explain insulators, semconductors, and conductors as described in the 'band theory for solids' (say) here: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html ?
Specifically I wish to use answers to this question to construct a useful visualisation of this aspect - trying to explain to lay people why some solids are transparent and some are semiconductors (or both) and using the bandgap to do so. See a basic, perhaps rushed, explanation of transparency started here: http://www.youtube.com/watch?v=Omr0JNyDBI0
There are two good reference questions here: Transparency of materials and followup here: Why isn't light scattered through transparency?
So of course its not just about bandgap but also how classical waves are built up from a quantum substrate and materials with structures smaller than the wavelength of light. That's my visualisation challenge...
I intend to show:
- high energy X-rays make many solids appear to be transparent because they are not absorbed vs the energies in IR, visible, and UV light for some materials.
- photons vs electrons being fired into a material
- glass structure vs crystal lattics or random structure solids
- opaque thin carbon vs transparent thick diamond and glass - why is paper opaque at visible light frequencies
- QED to classical wave showing how one leads to the other and how each model explains transparency
- Conduction, semiconduction, insulation and bandgaps and their relation to visible light energy transparency
- and probably some other aspects.
To reiterate my question: How does the bandgap theory of solids link transparency to conduction and valence bands (or other bands) ?
Feel free to suggest mechanisms for visualisation or any other contributing factors to explain this property of QED.
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