Technical improvement of the photoluminescence cell and its coupling to a dynamic vacuum system allow to avoid quenching phenomena. These results in emission spectra of MgO, which are better-resolved and more stable in time, leading to a better characterization of the very reactive oxide ions, i.e., those in low coordination. Apart from a more precise assignment of the spectra, new developments are proposed to evaluate the relative distribution of ions of low coordination. Discrimination of the oxide ions with different coordination numbers is also possible by studying in situ their interaction with propyne as a probe molecule.