Capture Modes Revealed by the Study of Line Intensities in GaP Pair Spectra

The capture mechanisms preceding photon emission by donor-acceptor pairs were clarified by the study of spectral-line intensities. Strong violations of the rule "equal intensities per donor-acceptor pair" were found in GaP under conditions of low excitation. Abrupt changes of intensity with changing separation of the donor-acceptor pair were attributed to changes in capture mode, and were related to critical dissipation energies in the capture process. The closing of capture channels and phonon resonance capture adequately explained the two kinds of observed intensity anomalies. An accurate calculation of the critical energies required the evaluation of multipole, van der Waals, and polarization energies. This led to a unique method of determining the polarizability of impurity atoms in solids. The measured polarizabilities of donors and acceptors in GaP are smaller than predicted by the model of a hydrogenic atom in a dielectric continuum.