PREPARATION, THERMAL-STABILITY AND LUMINESCENCE PROPERTIES OF SELECTED RARE-EARTH OXYCARBONATES

A comparative TG and DTG study of the preparation and thermal stability of selected rare earth oxycarbonates, (REO)2CO3 (RE = La and Gd), shows that the ease of formation as well as the stability of these compounds decreases strongly with increasing atomic number of the host cation. According to X-ray powder diffraction analyses, the RE oxycarbonates obtained as decomposition products of acetate and carbonate hydrates belong to the tetragonal IA-type. UV- and dye laser-excited luminescence studies of Eu3+-doped (LaO)2CO3 and (GdO)2CO3 reveal the presence of two different sites for the host cation. One of the sites resembles closely that prevailing in the tetragonal RE oxysalts, i.e. oxyhalides, oxysulphates, oxymolybdates and oxynitrates. A crystal field analysis carried out on the F-7(1) and F-7(2) level schemes according to a C2v site symmetry confirms this hypothesis.