Polarization-resolved optical spectra of coinage metal monomers and dimers M-n (M = Cu, Ag, Au; n = 1, 2) at ideal O2- sites of MgO(001) as well as at oxygen vacancies, F-s and F-s(+), of that surface were established using a computational approach based on linear response time-dependent density functional theory. Calculations were performed for structures determined by applying a generalized-gradient density functional method to cluster models embedded in an elastic polarizable environment. This embedding scheme provides an accurate description of substrate relaxation and long-range electrostatic interaction. We compared the optical properties of adsorbed atoms and dimers with those of the corresponding gas-phase species and we systematically analyzed trends among congeners.