Charged Frenkel excitons in organic crystals

Citation
Vm. Agranovich et al., Charged Frenkel excitons in organic crystals, CHEM PHYS, 272(2-3), 2001, pp. 159-169
Citations number
33
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
CHEMICAL PHYSICS
ISSN journal
0301-0104 → ACNP
Volume
272
Issue
2-3
Year of publication
2001
Pages
159 - 169
Database
ISI
SICI code
0301-0104(20011015)272:2-3<159:CFEIOC>2.0.ZU;2-F
Abstract
In molecular crystals a charge carrier and a molecular (Frenkel) exciton ar e attracted to each other. This attraction arises from the increase of the molecular static polarizability upon electronic excitation, and may be resp onsible for the formation of a two-particle bound state of the exciton and the free charge. Such charged Frenkel excitons are analogous to trions (bou nd states of a Wannier-Mott exciton and a charge carrier) in inorganic semi conductors. In this paper we develop a theory of charged excitons in molecu lar crystals, and apply this theory to study the spectra of charged Frenkel excitons in two-dimensional structures, which serve as a rather good appro ximation for layered crystals like anthracene, tetracene. We show that the binding energy of charged Frenkel excitons can be of the order of several h undred cm(-1). Thus, they may be stable at room temperatures, in contrast t o trions in inorganic semiconductors. Particularly interesting is the possi bility of forming charged triplet excitons in the crystal of tetracene wher e the energy of the lowest triplet exciton is much smaller than the energy of the lowest excitation in ions. This circumstance prevents the transforma tion of charged triplet excitons into an ion excitation with short lifetime and promotes the formation of rather stable charged triplet excitation. We briefly discuss the optical properties of charged Frenkel excitons and the effects of a static electric field. (C) 2001 Published by Elsevier Science B.V.