Frenkel exciton scattering at microcrystallite surfaces caused by electricdipoles and monopoles

A theory of exciton scattering by electric charges located on microcrystall ite surfaces is developed. The surface charges are assumed to be either ele ctric monopoles or dipoles. When monopoles are present on microcrystallite surfaces, surface excitons are created in microcrystallites in which the si zes are larger than a critical value. On the other hand, when electric dipo les are present at microcrystallite surfaces, surface excitons are always c reated irrespective of the microcrystallite size. The theory is applied to explain the surplus exciton bandwidth observed in anthracene microcrystalli tes, which indicates the presence of surface scattering. The theory also pr edicts the presence of an additional and intense exciton absorption line wh ich appears on the high-energy side of the host exciton absorption band. (C ) 1999 Elsevier Science B.V. All rights reserved.