RESUMEN
Simultaneous emission lines around 1.05µm, 1.3µm, 1.8µm, 2.1µm and 2.7µm have been observed in Li7La3-xNdxHf2O12:Ho3+ (x=0.00-0.15) under 808nm laser diode excitation. Near-infrared luminescence due to holmium ions with residual concentration in the Li7La3Hf2O12 host has been studied. The intensity of 2.1 and 2.7µm lines associated with 5I7â5I8 and 5I6â5I7 transitions in Ho3+ depends on the neodymium codopant concentration. This result indicates that Nd3+ ions can be potentially used as sensitizers for Ho3+ ions to stimulate the intense near-infrared emission in this system. Possible energy transfer mechanisms between lanthanide ions have been briefly discussed.
RESUMEN
Two new solid MO(OH)2 (M = Zr, Hf) oxyhydroxides have been synthesised by an ion-exchange reaction from Li2MO3 (M = Zr, Hf) precursors obtained by a citrate combustion technique. The crystal structure of the oxyhydroxides has been solved by direct methods and refined using Rietveld full profile fitting based on X-ray powder diffraction data. Both oxyhydroxides crystallize in a P2(1)/c monoclinic unit cell and have a structure resembling that of the related salts. Detailed characterisation of the fine-structure features and chemical bonding in precursors and oxyhydroxide powders has been performed using vibrational spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, pair distribution function analysis and quantum-chemical modelling.
RESUMEN
Crystal structures of TiO(OH)(2) and Li(2)TiO(3) have been studied in detail and refined using X-ray powder diffraction data. Both compounds possess a high concentration of defects in the structure. The crystal structure of the Li(2)TiO(3) salt obtained at 700 degrees C reveals stacking faults of LiTi(2) metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3(1)12. The possibility to stabilise this imperfect state increases the mobility of the Li(+) ions in the structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)(2). The crystal structure of TiO(OH)(2) belongs to the layered double hydroxide structure type with the 3R(1) sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)(2)OTi(2)O(OH)(2)]. TiO(OH)(2) is the first layered double hydroxide structure formed by a cation with oxidation state +4 only.
