Diffusion of Frenkel excitons in anisotropic crystals

Abstract

AbstractThe temperature dependence of the diffusion tensor Dik(T) of coherent excitons in anisotropic molecular crystals is considered. The influence of such exciton energetic band peculiarities as effective mass tensor anisotropy and nonanalyticity of exciton energy on the dependence Dik(T) is analyzed. It is shown that the dependence D ∼ T−1/2, which is characteristic of isotropic crystals, is retained only at weak anisotropy of the effective mass tensor mmax/mmin ≈︁ 1 with no regard for nonanalyticity. At the same time, at great values of the nonanalytic part of the exciton energy the diffusion tensor component dependences vary from Daa ≈︁ Dcc ∼ T−1 ≪ Dbb ∼ T−2 at weak anisotropy of the effective mass tensor to Daa ≈︁ Dcc ≈︁ const ≪ Dbb ∼ T−3/4 at strong anisotropy.