Frenkelexciton

Frenkel excitons are collective electronic excitations in molecular crystals or solids. Unlike charge-transfer excitons, where an electron and hole are separated by a significant distance, in a Frenkel exciton, the electron and hole are bound to the same molecule or unit cell. This tight binding means the exciton radius is comparable to the lattice constant. Frenkel excitons are therefore localized excitations.

The concept of Frenkel excitons was introduced by Yakov Frenkel in 1931. They arise from the interaction of excited molecules within a crystal lattice. When one molecule in the crystal absorbs a photon and becomes electronically excited, this excitation can then transfer to neighboring molecules through dipole-dipole interactions. This energy transfer process is essentially the movement of the excitation, not the physical movement of an electron or hole across the crystal.

Frenkel excitons play a crucial role in the optical properties of many materials, including organic semiconductors, molecular crystals, and some ionic crystals. They are responsible for phenomena such as light absorption and emission in these materials. The delocalization of the exciton over a few molecular sites influences its energy and lifetime. The study of Frenkel excitons is important for understanding energy transport in photosynthesis and for the development of organic electronic devices like OLEDs and organic solar cells.