The photoluminescence characteristics of compounds ALn(MO₄)₂, with A = Li, Na, K; Ln = Y, La, Gd, Lu, M = Mo, W, are analyzed as a function of their structure. The influences of cation size and electronegativity are discussed in relation with the Struck and Fonger theory, with a view to developing one or more of those compounds as phosphors in relation with the development of white LEDs. It appears that there are various excited states implied in the absorption process, with partially radiative transfer between them. All the radiative mechanisms are strongly related to temperature. Due to their electronegativity, tungstate compounds are the most promising, compared to molybdate ones, especially those in the monoclinic P_2/n structure.