Unusual luminescence spectra with a strong D 5 0 → 7 F 0 line, a high position of the 5D 0 level and the occurrence of two lines close to 16550 cm - 1 , i.e. in a frequency domain at the border between D 5 0 → 7 F 2 and D 5 0 → 7 F 1 transitions, have been evidenced in the case of cordierite, Mg 2 Al 4 Si 5 O 1 8 :Eu, mullite, 2Al 2 O 3 .SiO 2 :Eu and lanthanum disilicate, La 2 Si 2 O 7 :Eu. By comparison with results on apatites and some fluorides, these unusual spectra have been attributed to the presence of a strong and anisotropic crystal field due to an Eu-O bonding.