A.A. Onton, R.C. Taylor
Physical Review B
We report the first direct evidence of rotational levels of vibronic states in solids. These levels are associated with the ground states of shallow acceptors and provide the basis of a detailed understanding of the fine structure or "undulations" in emission spectra derived from bound excitons in GaP. This explanation is contrasted with one proposed recently by Hopfield, Kukimoto, and Dean. © 1972 The American Physical Society.