[CrimpJiggler]

In college I did a Wittig reaction with diethylbenzyl phosphonate and cinnamaldehyde and did a TLC on the product. I used a silica TLC and visualises it in a UV chamber and noticed that one of the spots was blue under the UV. The TLC plate itself gives off green light under UV, this is the first time I've seen anything turn blue under UV. What is the theory behind this? Am I right in assuming that the product itself is fluorescent and gives off higher energy blue light after absorbing UV radiation?

[Arkcon]

Remember, the longer wavelength light has less energy.  So visible light has less energy than ultraviolet -- its right there in the name.  But yes, you are correct, both the fluor mixed with the silica on the plate and your product are fluorescent.  Pretty nice outcome, you should now be able to check your expected products and find some info on which are fluorescent under UV.  Visible fluorescence is uncommon enough that, when it does happen, its usually noted.