Energy levels of nitrogen-nitrogen pairs in gallium phosphide

It is proposed that the line spectrum of nitrogen-nitrogen pairs in gallium phosphide arises from the recombination of an exciton situated at one nitrogen atom, its energy being perturbed by the strain field of a second nitrogen atom. The model predicts a series of lines with energies displaced from a series limit by an amount βprimeγ NN -3 , with βprime a constant and γ NN the nitrogen-nitrogen separation.