LUMINESCENCE PROPERTIES OF LA1-XTMXTA7O19

The luminescence properties of Tm3+ in La1-xTmxTa7O19 solid solutions were examined systematically. The substitution of Tm3+ for La3+ was carried out by a decomposition reaction of nitrates involving the corresponding constituents of 1200-degrees-C in air. X-ray diffraction patterns of the solid solutions indicated that the crystal structure consisted of a network of (La1-x3+Tmx3+, Ta5+)-O2- polyhedra interstratified with a double layer of Ta5+-O2-polyhedra. According to the excitation and emission spectra, the most intense emission was found near 460 nm and quenched above x = 0.14 in La1-xTmxTa7O19. Also, lifetime results verified that the emission could be assigned not to the transition 1G4 --> H-3(6), but to transition 1D2 --> H-3(4). Upon cathode ray excitation some emissions of Tm3+ were superimposed by a broad emission due to the clusters of Ta5+-O2- polyhedra. As a result, a low dimensional arrangement of Tm3+ was much more preferable for getting intense emission because it reduced the energy migration between Tm3+ ions.