The X-ray excited luminescent emissions of samples of Nasicon (NASuper-Ionic-CONductor) compounds of different stoichiometries were recorded vs. wavelength in the 280 to 560 nm range. The spectra show main peaks near 300 nm, with wavelengths and intensities depending on the sodium content of samples. These peaks are ascribed to radiative recombinations of electron-hole pairs trapped by Frenkel defects caused by the displacement of sodium ions in lacunar sites. Analysis of the recorded spectra highlights the effect of stoichiometry on ionic conductivity. (C) 2000 Elsevier Science Ltd. All rights reserved.