Synthesis of rare earth polyborates using molten boric acid as a flux

Hydrated rare earth hexaborates H(3)LnB(6)O(12) (Ln = Sm-Lu) have been synthesized by using molten boric acid as the reaction medium. H(3)LnB(6)O(12) decomposes at certain temperatures to form anhydrous pentaborates LnB(5)O(9) (Ln = Sm-Er) or orthoborates LnBO(3) (Ln = Tm-Lu). The crystal structures of the hexaborates and pentaborates have been determined by single-crystal and powder diffraction techniques. The hydrated hexaborates H(3)LnB(6)O(12) crystallize in a trigonal structure in the space group R3c, which contain a six-membered ring B6O15 as a fundamental fragment. Anhydrous pentaborates LnB(5)O(9) crystallize in a tetragonal structure that is built up with B4O9 and BO3. LnB(5)O(9) decomposes at higher temperature to metaborates (Ln = Sm-Tb) and orthoborates (Ln = Dy-Er). A phase diagram is presented that shows the stable range of both H(3)LnB(6)O(12) and LnB(5)O(9). The luminescent property of the europium-doped GdB5O9 was studied.Chemistry, PhysicalMaterials Science, MultidisciplinarySCI(E)58ARTICLE124963-49681