Abstract The luminescence properties of the system Na 5 (Gd, Eu)(WO 4 ) 4 are reported. The intensity of the vibronic sidebands in the excitation spectra of the Eu 3+ emission increases with the Eu 3+ concentration, whereas in the emission spectra this intensity is concentration independent. This is explained tentatively with a model involving the 7 F and charge-transfer states of Eu 3+ and the charge-transfer state of WO 2− 4 . Vibrational frequencies are derived from the spectra. Multistep energy migration over the Eu 3+ sublattice is not observed in Na 5 Eu(WO 4 ) 4 . The luminescence of about 10% of the Eu 3+ ions is quenched by single-step energy transfer to acceptors. Single-step energy transfer also occurs from WO 2− 4 to Eu 3+ .