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I ran an experiment using translucent single crystal solids. I modified the solids along the way using different chemical/temperature environments. After every stage, I ran the samples through a UV-VIS spectrometer (maybe it was technically a spectrophotometer, I'm a bit confused by the distinctions.

This spectrometer showed a beautifully clear difference in my absorption spectrum that appears to match up with what I am seeing in the other tests and properties of the samples. Namely, as I increase the temperature/chemistry of the modification, the absorption increases across different wavelengths and the cutoff frequency - the frequency at which everything is absorbed - increases from the UV range to the visible range.

My question is two fold:

(1) The formulas I am finding to get the information I need - such as band gap information - appear to rely on the sample being suspended as particles in some medium. My sample is a solid sheet of material about 0.5mm thick. The cuvette that I have been using is 1cm thick, leaving room for my sample to rattle about (though I took pains to make sure it was in the same position each time). How do I go about converting the suspension formulas to something I can use on my solid?

(2) This is more to save me some time and a favor owed: Given that you know how to answer (1), can you give me a general way to get band gap information out of this data from a solid?

Thanks, Sam

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up vote 1 down vote accepted

If you just want the band gap use a Tauc plot. You don't need absolute values for the absorption coefficient, so it doesn't matter if your material is a film or a dispersion in some other medium.

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Thanks so much for this information! Do you happen to know if the Tauc plot will work for single crystals? I forgot to mention, but I just edited the post, that my solid is a single crystal. Again, thanks! – pballjew Apr 26 '13 at 14:16
Yes it will work for a single crystal – John Rennie Apr 26 '13 at 14:31

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