For the sake of clarity, the results of this investigation are presented in two parts; first we discuss the lithium donor in silicon, and later the lithium-oxygen interaction in silicon. We present here a discussion of information which is common to both aspects of the problem. The data is presented in the form of absorption spectra in which the absorption coefficients are due only to the absorption centers introduced into the silicon samples during the diffusion process. The instrumental band width ( full width at half maximum) is indicated in each case for the energy regions in which the principal absorption resonances occur. / Ph. D.