  We formulate a theory of low-temperature, stationary photoluminescence from a
quantum-dot molecule composed of two spherical quantum dots whose electronic
subsystems are resonantly coupled via the Coulomb interaction. We show that the
coupling leads to the hybridization of the first excited states of the quantum
dots, manifesting itself as a pair of photoluminescence peaks with intensities
and spectral positions strongly dependent on the geometric, material, and
relaxation parameters of the quantum-dot molecule. These parameters are
explicitly contained in the analytical expression for the photoluminescence
differential cross section derived in the paper. The developed theory and
expression obtained are essential in interpreting and analyzing spectroscopic
data on the secondary emission of coherently coupled quantum systems.
