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The radiative decay of excitons in thin films is studied. The exciton modes capable of radiating are found to be superradiant, in contrast to the case of excitons in a bulk crystal. . It is estimated that this radiative decay mechanism will dominate over the other decay mechanisms such as those due to phonons or lattice imperfections.

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Using measurements of polarization-dependent soft-x-ray absorption and band-structure calculations including the on-site Coulomb interaction, we investigated the symmetry of the intrinsic 3d holes in the lowdimensional quantum magnet LiCu 2 O 2 with edge-sharing spin chains. The Cu L-edge and O K-edge measurements with in-plane and out-of-plane E vectors of x ray reveal the orbital character of the valence states of Cu on different sites. The unoccupied 3d states of nominal Cu 2+ exhibit predominantly xy symmetry, whereas 3d holes of 3z 2 − r 2 symmetry reside on the nominal Cu + sites. Both the experimental observations and theoretical calculations agree on the hybridization of the O 2p and Cu 3d states above the Fermi level. The existence of 3d holes on Cu + enhances the interlayer magnetic coupling.