A study was made of the photoluminescence spectra of excitons which were bound to iso-electronic defects, B711 (with principal no-phonon line of 1.13768eV), that were created in P-doped material (grown in a H atmosphere) by irradiation with thermal neutrons. During the measurements, the samples were subjected to magnetic fields of up to 12T and to uniaxial stresses. The C3v symmetry of these defects was deduced unambiguously from the dependences of the Zeeman splitting and of the intensities of the spectral components upon the magnetic-field orientation. The ground state of the bound exciton was split into a doublet with an energy separation of about 30eV. This splitting, which was not evident in zero-field spectra (because of selection rules), resulted in the appearance of an additional spectral component in a magnetic field. By using group theoretical methods, a Hamiltonian was constructed for excitons that were bound to the B711 iso-electronic center. This took account of electron-hole coupling and of interactions with external perturbations. The phenomenological parameters of this Hamiltonian were deduced from an optimal fit between the theoretical and experimental dependences of the photoluminescence peak positions, and their amplitudes under the influence of magnetic fields and uniaxial stresses. A model for these bound excitons was proposed which explained all of the experimental observations.

A.S.Kaminskii, E.V.Lavrov, V.A.Karasyuk, M.L.W.Thewalt: Physical Review B, 1994, 50[11], 7338-43