The polarized absorption spectra of Nd3+-doped Na+ beta''-alumina have been treated theoretically for five neodymium concentrations. The perturbing crystal field, needed in the Judd-Ofelt analysis, is calculated from a molecular-dynamics simulation for each composition. Oscillator strengths and Judd-Ofelt intensity parameters are calculated using a point-charge model at each time step in the simulation for each of the Nd3+ ions in the simulation box. A study of the effect of the dynamics of the system on these parameters was also made. The theoretical results thus obtained are compared to experiment. It is shown that the absorption spectra can be explained essentially on the basis of the special structural situation of the Nd3+ ions in these materials.