Résumé
PCCP 19 1369 (2017) We have studied in this work the effect of increasing structural disorder on the persistent luminescence of Cr $^{3+}$doped zinc gallate spinel. This disorder was introduced by progressive substitution of Zn $^{2+}$by Mg $^{2+}$ions, and was studied by photoluminescence, X-ray diffraction, extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) and electron paramagnetic resonance (EPR) spectroscopy. It was found that increasing Mg/Zn substitution decreases the number of Cr $^{3+}$in undistorted sites, and increases the number of Cr $^{3+}$with neighbouring antisite defects and with neighbouring Cr $^{3+}$ions (referred as Cr clusters), which in turn decreases the intensity of persistent luminescence. Both XANES and EPR spectra could be simulated by a linear combination of Cr $^{3+}$spectra with three types of Cr $^{3+}$environments. The increasing disorder was found to be correlated with a decrease of the average Cr-O bond length and a decrease of crystal field strength experienced by Cr $^{3+}$ions.