exciton (rus. экситон) — (from Latin excito meaning "excite") a quasiparticle that corresponds to the electronic excitation in the dielectric or semiconductor crystal, which migrates over the crystal without being related to any transfer of electrical charge or of mass.

Description

The way an exciton is produced can be described as follows: when light is absorbed, an electron from one energy level (or band) jumps to a higher level, leaving a positively charged hole in its place at the original level (band), with the electron and the hole being bound with the Coulomb attraction. Exciton is actually a bound state of an electron and a hole, which is similar to the state of an electron in a hydrogen atom.

Excitons in semiconductors with a high dielectric constant (Wannier-Mott excitons) are large in size (many times larger than the distance between atoms) and have low energy (about 0.1 eV). In materials with a low dielectric constant, such as molecular crystals, excitons (termed Frenkel excitons) are much smaller, may be on the same lattice site and have energy of about 1 eV. Single-wall carbon nanotubes can have both types of excitons formed.

Excitons also occur in biological systems, such as photoantennae, where the exciton is an excited electronic state of a сhromophore molecule caused by light absorption. As chromophores interact with adjacent molecules, it leads to the transfer of electronic energy from one molecule to another, which looks like an exciton moving along the photoantenna (see photosynthesis).

Excitons have a finite lifetime in all systems. It is on the scale of nanoseconds with molecular excitons. Electron-hole recombination or molecule transition from the excited to the ground state results in light emission (fluorescence).

Authors

  • Eremin Vadim V.
  • Naymushina Daria A.
  • Streletskiy Alexey V.

Sources

  1. Physical Encyclopedic Dictionary (in Russian) // Ed. by. А. М. Prohorov. — Moscow: Sovetskaja ehnciklopedija, 1984.
  2. Exciton // The Great Soviet Encyclopedia (in Russian), 3rd. Edition // Moscow: Sovetskaja ehnciklopedija, 1969– 1978. — http://bse.sci-lib.com/article125695.html (reference date: 12.12.2011).
  3. Davydov A. S. Theory of molecular excitons. — Plenum Press, 1971 - 313 pp.

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