The nonuniform broadening of optical spectra is analyzed for two types of rare-earth-activated disordered laser crystals: substituted garnets and yttria-stabilized zirconia (ZrO2–Y2O3). By decomposing nonuniformly broadened, composite R3+ absorption and luminescence bands, several principal centers (K and L for Eu3+ andA, B, C, and D for Nd3+) are identified and correlated with particular configurations of the near-neighbor environment of the activator ions (optical centers). It is shown that the formation of activator associates has a weaker effect on the optical spectra than the nearest neighbor coordination of the activator.