Exciton-phonon coupled states in CuCl quantum cubes

Abstract

The size dependence of excitonic states and vibrational modes in CuCl cubic quantum dots embedded in NaCl crystals was studied by means of site-selective persistent spectral hole burning spectroscopy. It is shown that the interaction of the longitudinal optical (LO) phonon with the exciton results in the formation of coupled exciton-phonon modes when the energy of the LO phonon approaches the energy spacings between the ground and excited states of the exciton. The energy anticrossings of the LO phonon modes with two higher optically allowed excited states of the exciton in CuCl QD’s were clearly observed at confinement energies of about 10 and 6 meV, respectively. In addition, the linewidth of the LO phonon sideband in CuCl QD’s in NaCl crystals was found to increase abruptly from 0.3 meV to about 1.2 meV at a confinement energy of about 23 meV, which appears to result from the exciton-phonon mixing of the LO phonon mode with the first excited state of the exciton. The experimental results are qualitatively understood by the LO phonon renormalization theory. © 2000 The American Physical Society.