The formation of donor-acceptor pairs was studied by means of perturbed  angular correlation spectroscopy. In crystals which were doped with the 111In donor and an acceptor (N, P, As, Sb), the strength of the electric field gradient exhibited a systematic correlation with the bond length between the respective acceptor and the neighboring cation. In the case of N acceptors, an inward relaxation of the neighboring cations was suggested to occur.

V.Ostheimer, A.Jost, T.Filz, S.Lauer, H.Wolf, T.Wichert: Applied Physics Letters, 1996, 69[19], 2840-2