Luminescence properties of La1−χTmχTa7O19

Abstract

The luminescence properties of Tm3+ in La1−χTmχTa7O19 solid solutions were examined systematically. The substitution of Tm3+ for La3+ was carried out by a decomposition reaction of nitrates involving the corresponding constituents at 1200 °C in air. X-Ray diffraction patterns of the solid solutions indicated that the crystal structure consisted of a network of (La1−χ3+Tmχstaggered|3+, 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 χ=0.14 in La1−χTmχTa7O19. Also, lifetime results verified that the emission could be assigned not to the transition 1G4 å 3H6, but to the transition 1D2 å3H4. 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.