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The Photodiode You Never Knew You Had
(hackaday.com)
This is a most excellent place for technology news and articles.
Using Diodes and their ilk as LEDs is the EE equivalent of "all mushrooms are edible, some only once"
The secret of all diodes is that they are all LEDs as well. The frequency determined by the bandgap. For most unfortunately, that means infrared and releasing the magic smoke.
Black body radiation emitting diode