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