Synthesis and luminescent properties of rare earth (Sm~(3+) and Eu~(3+)) Doped Gd_2Ti_2O_7 pyrochlore nanopowders

摘要

This work describes the synthesis and photoluminescent properties of rare earth (Sm~(3+) and Eu~(3+)) doped Gd_2Ti_2O_7 pyrochlore nanopowders. Pure-phase rare earth-doped Gd_2Ti_2O_7 nanoparticles of approximately 20-50 nm in diameter, as evidenced from X-ray diffraction and electron microscopy analysis, are produced via the mixed metal-citric acid complex method. A temperature of 880 ℃ is identified for the formation of the crystalline pyrochlore phase, based on a differential thermal analysis of Gd_2Ti_2 O_7 precursor gels. From photoluminescence excitation and emission spectra, measured at 10 K and room temperature, the energy levels of Sm~(3+) and Eu~(3+) ions in Gd_2Ti_2O_7 nanoparticles are obtained. The dependence of luminescence emission intensity and emission decays on rare earth concentration are measured and discussed. The strongest Sm~(3+) orange-reddish emission is observed for samples containing 2.5 at.% of Sm~(3+) ions, while in the case of Eu~(3+), the most intense emission is found for 15 at.% Eu~(3+) doping. The ~4G_(5/2) level lifetime decreases with an increase in Sm~(3+) concentration, from about 5 ms (for 0.1) -0.2 at.% of Sm~(3+)) to 2.4 ms (for 2.5 at.% of Sm~(3+)). With an increase in Eu~(3+) concentration in the Gd_2Ti_2O_7 nanoparticles, the Eu~(3+) ~5D_0 level lifetime decreases from ～5.9 ms (for 0.5 at.% of Sm~(3+)) to 3.1 ms (for 15 at.% of Sm~(3+)).