What semiconductor device glows different colours, depending upon its chemical composition?

A light-emitting diode (LED) is a specialized solid-state semiconductor device that emits photons (light) when electrical current passes through it in the forward direction. The specific color of the light emitted is determined by the band-gap energy of the chemical compounds used in the semiconductor material, such as gallium arsenide or indium gallium nitride. While fluorescent bulbs and neon bulbs also glow and emit light, they rely on ionized gases rather than solid-state semiconductor junctions. A vacuum diode is an older thermionic tube component that does not emit colored light based on chemical composition.