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LED's are normally made of Gallium/Aluminum/indium doped with Arsenide/Phosphide/Nitride. Actual colur and intensity of the LED determines correct semiconductor meterial. Also by varying the bandgap,the photon emission frequency of the LED ,hence the intensity are effected.
Here is one of the famous site that I know as electronics encyclopedia.It lists number of projects/applications. Givea proper search for what you want exactly