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 ⁷F₁ and ⁷F₂ level schemes according to a C_2v site symmetry confirms this hypothesis.