Two-Photon Absorption in Crystalline Anthracene and Naphthalene Excited with a Xenon Flash

Abstract

Two‐photon absorption and delayed fluorescence are observed in both anthracene and naphthalene using a 5‐μsec xenon flash lamp. It is shown that coherence and monochromaticity are not important in two‐photon absorption. It is also demonstrated that the two‐photon absorption process does not involve triplet excitons. In anthracene the two‐photon rate constant δ≃8×10^—29 cm sec and is about this value in naphthalene. Mechanical imperfections play an important role in processes involving excited states in naphthalene monocrystals. The effect of imperfections is such that only an order‐of‐magnitude value for the intersystem crossing constant can be evaluated at the moment: τ_fk_st≃10^—1, where τ_f is the fluorescence lifetime.