A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

OXYBROMIDESOne oxy-bromide, or oxide bromide, is used commercially; LaOBr, doped with theblue-emitter thulium, is an important X-ray phosphor[1]. The compound has a high intrinsicabsorption of X-rays and a high efficiency for the conversion of X-radiation to visible radiation.The lanthanum compound (and the Ln analogues) can be made by reacting the oxide withammonium bromide initially at 500°C followed by recrystallization at 800 - 1000 °C in a fluxcontaining bromides. The oxalates can also be used as the Ln source as they are more reactive thanthe corresponding oxides.Like the oxychlorides, the heavier Ln oxybromide compounds are thermally less stable thanthe light-Ln analogues; LaOBr, for example, is stable to above 1000°C. The oxybromides aresusceptible to attack by moisture and have to be protected in use. The hydrolysis seems to beinitiated by traces of unreacted bromide ions at the surface of particles.3 LaOBr + 3 H 2 O => 3 La(OH) 2 BrThe heavier-Ln compounds will decompose further:=> Ln(OH) 3 + LnBr 3The oxybromides, like the oxychlorides, contain the [LnO] n n+ layers and also adopt theBiOCl structure.[1] New X-Ray Phosphors, L.H.Brixner, Materials Chem. Phys., 1987, 16(3-4), 25322