Thermally activated population of microcavity polariton states under optical and electrical excitation

We examine the luminescence from optical microcavities containing an organic semiconductor in the regime of strong exciton-photon coupling. The ratio of luminescence from the upper polariton branch to the lower polariton branch is studied as a function of microcavity detuning and temperature under both optical and electrical excitation. The population of the upper polariton branch is modeled by means of thermal activation from an uncoupled exciton reservoir. Here, the activation energy for the population of the upper polariton branch is equal to the energetic separation between the exciton reservoir and the upper branch at the angle of detection. Agreement is obtained with this model under both optical and electrical excitation using measurements of angle-resolved microcavity reflectivity and luminescence.