GaAs is one of the most important direct band gap semiconducting material used in light emitting diodes (LED). With suitable combination of elements, the emission wavelength can be tuned.

GaAs          - 870 nm (IR)
GaAs0.6P0.4   - 650 nm (red)

The composition of In and Ga in InGaN can be fine tuned to obtain blue LED which finds significant applications in blue-ray's. In addition to the above a number of semiconducting compounds which emits wavelength from IR to UV ranges could be obtained simply by adjusting the band gap.

Polyacetylene is a conductive polymer used in Polymer LED's. Tris(8-hydroxyquinolinato)aluminium is used in organic LED's.