The 2.8-mm emission of Er-doped low silica content calcium aluminate glasses sensitized by Yb is investigated using conventional spectroscopy. The experimental data are quantitatively analyzed in terms of the energy transfer among the Yb and Er ions. The energy transfer rate by dipole-quadrupole mechanism was inferred to be larger than by dipole-dipole mechanism. Using the Dexter model of energy transfer, the microscopic parameters of energy transfer by dipole-dipole mechanism were calculated. It was found that the Yb31→Er31 energy transfer constant is 2.6 times greater than the back-energy transfer.