Pollmann-Büttner variational method for excitonic polarons

We extend the variational method of Pollmann and B\"uttner for the effect of polar lattice coupling on effective-mass excitons. Their results correspond to a correction of the dielectric constant; we have added the correction for the polaron mass. We find the polaron mass is strongly quenched to nearly the bare-mass value. We give an analytic result for the case of equal hole and electron masses, and present tabular functions enabling easy binding-energy determinations for any parameter values. Exciton and donor binding energies for specific I-VII and II-VI compounds are given. For the I-VII compounds, donor binding energies are less than exciton binding energies. The stronger screening of the heavy ion apparently overwhelms the heavier reduced mass of the donor.