Synthesis of New LnxBi2-xSe3 (Ln: Sm3+, Eu3+, Gd3+, Tb3+) Nanomaterials and Investigation of Their Optical Properties

New Ln(x)Bi(2-x)Se(3) (Ln: Sm3+, Eu3+, Gd3+, Tb3+) based nanomaterials were synthesized by a co-reduction method. Powder XRD patterns indicate that the Ln(x)Bi(2-x)Se(3) crystals (Ln = Sm3+, Eu3+, x = 0.00-0.44 and Ln = Gd3+, Tb3+, x = 0.00-0.50) are isostructural with Bi2Se3. 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 Bi2Se3 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 Bi2Se3 lattice. Emission spectra of europium-doped materials, in addition to the characteristic red emission peaks of Eu3+, show an intense blue emission band centered at 432 nm, originating from the 4f(6)5d(1) to 4f(7) configuration in Eu2+. EPR measurements confirm the existence of Eu2+ 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.