Electronic and vibronic states of the acceptor–bound-exciton complex ($A^0$,X) in CdS. II. Determination of the fine structure of the ($A^0$,$X_B$) electronic states by high-resolution excitation spectroscopy

In a previous paper [R. Baumert, I. Broser, J. Gutowski, and A. Hoffman, Phys. Rev. B 27, 6263 (1983)] it has been shown that high-density, high-resolution excitation spectroscopy gives new information on the electronic and vibronic excited states of the acceptor–bound-exciton complex ($A^0$,$X_A$) with two holes from the A valence band in CdS. We now report on corresponding results for the ($A^0$,$X_B$) configuration which includes one hole from the second B valence band. This complex is unstable for a very fast B→A hole conversion, and therefore gives rise to a set of excitation resonances of the $I_1$ luminescence arising from the ($A^0$,$X_A$) recombination. A detailed theoretical analysis of the energetic structure of the ($A^0$,$X_B$) complex including the dependence on the excitation intensity and on an applied magnetic field allows the correct assignment of the excitation resonances to the ($A^0$,$X_B$) fine-structure levels originating from the interparticle-exchange interactions. It is shown that the magnetic field is a suitable means of distinguishing the different ($A^0$,$X_B$) ground-state levels. The magnetic field also creates allowed transitions which are dipole forbidden in the zero-field case. A self-contained model of the ($A^0$,$X_B$) complex thus can be developed, including all symmetry states and yielding adequate values for the exchange energies within the complex.