On hexagonal perovskites with cationic vacancies. 32

In the series Ba/sub 2-y/Sr/sub y/La/sub 2-x/RE/sub x/MgW2vacantO12 the Ba2+ can be completely substituted by Sr2+. All compounds crystallize in the rhombohedral 12 L-type (space group R-3m; sequence (hhcc)3). By doping the stacking polytypes with some of the trivalent rare earths efficient visible photoluminescence is obtained. The simultaneous incorporation of two different rare earth ions leads to two-color-phosphors, which, according to the excitation energy used, emit either mainly the typical spectrum from one or the other activator; the corresponding luminescence mechanism are discussed. (author)