Polariton lasing in organic semiconductor microcavities (Conference Presentation)

Abstract

A semiconductor-microcavity is an optical structure composed of two mirrors separated by a layer of semiconducting material. If the energy of the confined photon and excitonic transition are degenerate, interactions can occur in the strong-coupling regime, with the eigenstates of the system being cavity polaritons (a coherent superposition between light and matter). Due to their bosonic nature, cavity polaritons are able to undergo condensation to a macroscopically occupied coherent state. Polariton condensates can be optically pumped and then undergo decay by emitting coherent light, very much like an optically pumped laser. Here, we demonstrate evidence of polariton condensation in a microcavity containing a dispersed molecular dye. Our structures are based on two dielectric-mirrors placed either side of a film of the transparent matrix polymer polystyrene containing the fluorescent molecular dye BODIPY-Br. We first show using CW photoluminescence measurements that weakly-coupled excimer-like states in the BODIPY-Br, together with emission from the (0,1) vibrational transition are responsible for optically pumping polariton states along the lower polariton branch. We then explore the non-linear emission from control thin-films and cavities using pulsed laser excitation. We obtain strong evidence of non-linear photoluminescence with increasing excitation density, associated with a six-fold linewidth narrowing and a continuous blue-shift attributed to polariton interactions with other polaritons and the exciton reservoir. We believe that there is a large number of molecular dyes that could dispersed into a polymer matrix allowing polariton condensation to be realised at wavelengths spanning the entire visible and near infrared.