Spektrallücke

Spektrallücke, which translates to "spectral gap" in English, is a fundamental concept in condensed matter physics. It refers to the energy range in the excitation spectrum of a material where no electronic states exist. In simpler terms, it's an energy band where electrons cannot reside. This phenomenon is characteristic of insulators and semiconductors, distinguishing them from metals where the electronic energy bands overlap or are not fully occupied, allowing for free electron movement.

The existence of a spektrallücke is directly related to the material's electrical conductivity. Materials with a large spektrallücke typically behave as insulators because a significant amount of energy is required to excite electrons across this gap to a state where they can conduct electricity. In semiconductors, the spektrallücke is smaller, meaning less energy is needed to promote electrons into the conduction band, enabling them to conduct electricity under certain conditions, such as when exposed to heat or light. The size of the spektrallücke dictates the material's optical properties as well, influencing which wavelengths of light it absorbs or transmits. For instance, materials with a spektrallücke corresponding to the energy of visible light photons will absorb visible light, appearing opaque or colored.