Luminescence excitation of donor acceptor pairs in CdTe: Acceptor ground state splitting and associate energy transfers

Excitation spectroscopy of lithium-indium donor-acceptor pairs in CdTe is used to investigate the impurity interaction effect on the acceptor ground state. The interaction with a neighbouring donor atom causes a splitting of the degenerate hole state. Two sharp narrow lines, associated with the pair neutralization transition in the ground state sublevels, are observed up to pair separations of 70Å. The splitting can be accounted for by two possible mechanisms : a strain field around the acceptor, induced by the donor, or an electric field gradient, due to the charged donor. Comparison with experiments seems in favour of a Coulomb type perturbation.