Biexcitonic luminescence for "allowed" and "forbidden" polarization

We present theoretical and experimental results on biexcitons in CdS. On the basis of an accurate selection of the polarization of luminescence light from the M line, we obtain a good agreement with the hypothesis of the biexciton and a precise value for its ground-state half-energy (2.5497 eV ±{} 0.1 meV). We also discuss previous results obtained by other authors.