  A quantum cascade laser where the quantum wells in the active regions are
replaced by quantum dots with their atom-like discrete energy levels is an
interesting system to study novel features in optical spectroscopy. We study
structures suitable for diagonal lasing transitions in coupled dots, and
vertical lasing transitions in a single dot, in the active regions of the laser
device. The luminescence spectra as a function of electron number and dot size
show that for diagonal transitions, a significant amount of blue-shift in the
emission spectra can be achieved by increasing electron population in the
quantum dots as well as by decreasing the size of the dots.
