Gallium arsenide phosphide (GaP) diodes emit red light. Their light-emitting principle involves the release of energy as electrons and holes recombine in a PN junction, radiating visible light as photons. The material's band gap determines the wavelength (color) of the light.
Other common LED materials and their corresponding colors: Gallium phosphide (GaP): Green light
Silicon carbide (SiC): Yellow light
Gallium nitride (GaN): Blue light