Formation and properties of essentially nonequilibrium polaritons in small crystals seen through luminescence of solid xenon

Abstract

The formation of polaritonic states, shifted to both sides from the initial exciton level by about 0.1 eV, was observed through luminescence of solid xenon samples consisting of small crystalline grains. Unlike previous works, where the observed red polaritonic shift was small commensurably with a weak inelastic polariton–phonon scattering, a large polaritonic shift of luminescence is not due to energy dissipation, the energy conservation law being met due to equal probabilities for opposite-sign energy shifts. Such effect is possible if the crystalline grains are comparable in size with light wavelength, which provides the filling in of the interval of the longitudinal–transverse splitting by excitons with a significant oscillator strength. Besides, the sample structure must by perfect enough that the rate of exciton scattering is lower than the rate of the polariton formation through the exciton–photon coupling. The dynamics of polaritons, observed under such nonequilibrium conditions, has fundamental distinctions mirrored by a broad spectrum of polaritonic luminescence, its fast decay kinetics and an anomalously high quantum yield.