In this work the site location of several M3+ dopant ions in has been investigated by using optical (absorption and site‐selective fluorescence) techniques. Experimental results reveal that the regular cation sites, Li+ and Nb5+, are occupied in all cases and can be characterized optically. Additional crystal field sites, for and , have been detected by site selective spectroscopy. The effects on the M3+ optical spectra of the stoichiometry and the codoping with have been systematically investigated. The appearance of new sites for the M3+ ions, M3+‐Mg2+, is ascertained for .