Synthesis of new Ln_xBi_(2-x)Se_3 (Ln: Sm~(3+), Eu~(3+), Gd~(3+), Tb~(3+)) nanomaterials and investigation of their optical properties

摘要

New Ln_xBi_(2-x)Se_3 (Ln: Sm~(3+), Eu~(3+), Gd~(3+), Tb~(3+)) based nanomaterials were synthesized by a co-reduction method. Powder XRD patterns indicate that the Ln_xBi_(2-x)Se_3 crystals (Ln = Sm~(3+), Eu~(3+), x = 0.00-0.44 and Ln = Gd~(3+), Tb~(3+), x = 0.00-0.50) are isostructural with Bi_2Se_3. The cell parameter c decreases for Ln = Eu3+, Gd3+, Tb3+ upon increasing the dopant content (x), while a slightly increases. Changes in lattice parameters could be related to the radii of cations. SEM images show that doping of the lanthanide ions in the lattice of Bi_2Se_3 generally results in nanoflowers. For the terbium compound two kinds of morphologies (nanoflowers and nanobelts) were observed. UV/Vis absorption and emission spectroscopy reveals mainly electronic transitions of the Ln~(3+) ions. Emission spectra show intense transitions from the excited to the ground state of Ln~(3+) and energy transfer from the Bi_2Se_3 lattice. Emission spectra of europium-doped materials, in addition to the characteristic red emission peaks of Eu~(3+), show an intense blue emission band centered at 432 nm, originating from the 4f~65d~1 to 4f~7 configuration in Eu~(2+). EPR measurements confirm the existence of Eu~(2+) in the materials. Interestingly, for all samples starting at low Ln~(3+) concentration, the emission intensity rises to a maximum at a Ln~(3+) concentration of x = 0.2 and falls again steadily to a minimum at x = 0.45.