Homogeneous linewidths and confined-phonon sidebands of the resonant exciton luminescence of $\mathrm{CuCl}$ quantum dots

We investigated the resonant luminescence spectra of CuCl quantum dots in NaCl and glass matrices with high spectral resolution. The resonant luminescence consists of a sharp zero-phonon line accompanied by Stokes and anti-Stokes sidebands. We confirmed that the sidebands originate from lattice vibrations confined in the quantum dots. The observed ultrasharp homogeneous width of the zero-phonon line indicates a very long phase-relaxation time of the confined excitons at low temperature. The temperature dependence of the homogeneous width is explained by a two-phonon Raman process associated with the confined phonons.