Exciton-polaritons in a crystalline anisotropic organic microcavity

Investigation of polaritons in organic microcavities with strong light-matter interaction is of fundamental and practical interest. In the paper we study for the first time the dispersion of exciton-polaritons in a microcavity utilizing anisotropic organic crystals with one and two molecules per unit cell as optically active material. It is known that in bulk anisotropic organic crystals (like anthracene, tetracene and similar ones) the energies of Coulomb excitons are non-analytical functions of their wave vector k at small k (i.e. the energy of the exciton is different for different directions of the wave vector in the limit k --> 0). We show that this is not the case in a planar microcavity where Coulomb exciton states are two-dimensional and the energy of Coulomb excitons at small wave vectors is an analytical function. Also, in contrast to widely used inorganic microcavities, in an anisotropic organic microcavity the cavity photon modes with both possible polarizations mix with the exciton states in the formation of polariton states. We demonstrate that these two factors result for small wave vectors in an almost isotropic dispersion of polaritons in an anisotropic organic crystalline microcavity, which can be observed in reflection, transmission and photoluminescence spectra of organic microcavity. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.