What are Frenkel excitons?
Frenkel excitons are typically found in alkali halide crystals and in organic molecular crystals composed of aromatic molecules, such as anthracene and tetracene. Another example of Frenkel exciton includes on-site d-d excitations in transition metal compounds with partially-filled d-shells.
What are excitons explain?
exciton, the combination of an electron and a positive hole (an empty electron state in a valence band), which is free to move through a nonmetallic crystal as a unit.
What is a charge-transfer exciton?
1 Fundamentals of Charge-Transfer Excitons Excitons are atomic hydrogen-like bound electron−hole pairs that determine many optical and optoelectronic properties of solid materials. (1, 2) If the radius of the electron−hole pair is smaller than the unit cell dimension, we call this a Frenkel or molecular exciton.
What are the different types of excitons?
Wannier Exciton.
What is Frenkel defect explain it?
A Frenkel defect is a type of point defect in crystalline solids, named after its discoverer Yakov Frenkel. The defect forms when an atom or smaller ion (usually cation) leaves its place in the lattice, creating a vacancy and becomes an interstitial by lodging in a nearby location.
What are excitons and polarons?
Excitons and polarons play a central role in the electronic and optical properties of organic semiconducting polymers and molecular aggregates and are of fundamental importance in understanding the operation of organic optoelectronic devices such as solar cells and light-emitting diodes.
Are excitons particles?
It actually sounds like a subatomic particle, but it is a little more complicated than that. An exciton is a bound state of an electron and an electron hole and is technically a boson. You are probably familiar with the idea of an electron hole from semiconductor physics. Technically, it is a quasiparticle.
What is the origin of excitons?
Attraction between the electron and the hole causes their motion to be correlated and the resultant electron-hole pair is known as an exciton. It is an electrically neutral quasiparticle that exists in insulators, semiconductors and some liquids.
What are the charge carriers in semiconductors?
In n-type semiconductors they are electrons, while in p-type semiconductors they are holes. The less abundant charge carriers are called minority carriers; in n-type semiconductors they are holes, while in p-type semiconductors they are electrons.
What is Frenkel and Schottky defect?
Schottky defect occurs in those ionic crystals where the difference in size between cation and anion is small. Frenkel defect usually occurs in those ionic crystals where size of anion is quite large as compared to that of the cation. In Schottky defect, both cation and anion leave the solid crystal.
What is Frenkel defect and what are its conditions and consequences?
It creates a vacancy defect at its original lattice site and an interstitial defect at its new location. It is found in crystals: (i) with low co.no. (ii) Where there is large difference in the size of cation and anions e.g. ZnS, AgCl, AgBr, AgI. Due to this defect, the density doesn’t change.
What is meant by polaron?
Definition of polaron : a conducting electron in an ionic crystal together with the induced polarization of the surrounding lattice.
How do electrons move through a Frenkel exciton?
Although the electron and hole in a Frenkel exciton reside on the same molecule, they do have the ability to move through the crystal as a pair. This center-of-mass motion of the pair arises from electrostatic interactions between the electrons on different molecules.
What are Frenkel excitons in a bulk crystal?
2.5. Frenkel Excitons in a Bulk Crystal 2.5.1. General Hamiltonian and One-Exciton States We now turn to the special case of excitons in a molecular crystal, occupying an arbitrary Bravais lattice. Each unit cell of the crystal contains S molecules.
What are the peculiarities of St of charge transfer excitons?
As a brief intermezzo, we mention some peculiarities of ST of charge-transfer excitons. The electron–hole interaction energy in a charge-transfer exciton is of the order of e2 / a, where a is the distance between electron and hole. This energy may be a few eV.
What is the relationship between Frenkel excitons and ground state large radius?
This relationship for Frenkel excitons was derived by Agranovich and Konobeev [109]; it can be seen from its derivation that it is independent of the model and, therefore, is valid also for ground state large-radius excitons as well as for electrons and holes in semiconductors.