LEDs, or Light-Emitting Diodes, emit light at certain wavelengths due to the specific properties of the materials used in their construction and the underlying physics of electron energy levels.
LEDs are made from semiconductor materials, typically compounds such as gallium arsenide (GaAs), gallium nitride (GaN), or indium gallium nitride (InGaN). These materials have a property called a bandgap, which is the energy difference between the valence band (lower energy level) and the conduction band (higher energy level) in the electronic structure of the material.
When a forward voltage is applied to an LED, electrons in the valence band gain enough energy to jump into the conduction band, leaving behind "holes" in the valence band. This process is known as electron-hole recombination. As the electrons and holes recombine, they release energy in the form of photons, which is the light that the LED emits.
The specific wavelength, or color, of the emitted light depends on the bandgap energy of the semiconductor material. The energy of a photon is inversely proportional to its wavelength (E = hc/λ, where E is the energy, h is Planck's constant, c is the speed of light, and λ is the wavelength). Therefore, a larger bandgap corresponds to higher energy photons and shorter wavelengths of light, while a smaller bandgap corresponds to lower energy photons and longer wavelengths of light.
By carefully selecting the semiconductor material and its bandgap, manufacturers can engineer LEDs to emit light at specific wavelengths. For example, gallium arsenide phosphide (GaAsP) LEDs emit red or yellow light, while indium gallium nitride (InGaN) LEDs can emit blue, green, or white light.
It's worth noting that the precise control of the composition and structure of the semiconductor materials used in LEDs is crucial for achieving specific wavelengths. This control allows for the production of LEDs with different colors and enables their widespread use in various applications, such as lighting, displays, and optical communication.