Multicolor tunable luminescence and paramagnetic properties of NaGdF₄:Tb³⁺/Sm³⁺ multifunctional nanomaterials

Tb(3+) and/or Sm(3+) doped NaGdF4 luminescent nanomaterials have been successfully synthesized by an SDS-assisted one-step hydrothermal method. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray energy dispersive spectrometer (EDS), photoluminescence (PL) spectra and a vibrating sample magnetometer (VSM). The results show that the synthesized samples are all pure β-NaGdF4. The as-prepared Tb(3+) or Sm(3+) doped samples show strong green and yellow emission, originating from the allowed (5)D3→(7)F(J) (J = 5, 4, 3, 2) and (5)D4→(7)F(J) (J = 6, 5, 4, 3) transitions of the Tb(3+) ions and the (4)G(5/2)→(6)H(5/2), (6)H(7/2), (6)H(9/2) transition of the Sm(3+) ions. Based on the excitation wavelengths, multiple (yellowish green, yellow, white) emissions are obtained by Sm(3+) ion co-activated NaGdF4:Tb(3+) phosphors. Moreover, an energy transfer from Tb(3+) to Sm(3+) is observed, which is justified through the luminescence spectra and the fluorescence decay curves. Furthermore, the resonance-type energy transfer from Tb(3+) to Sm(3+) is demonstrated to occur via the dipole-dipole mechanism. In addition, the obtained samples also exhibit paramagnetic properties at room temperature. It is obvious that these multifunctional Tb(3+), Sm(3+) co-doped β-NaGdF4 nanomaterials, with tunable multicolors and intrinsic paramagnetic properties, may have potential application in the fields of full-color displays, biological labels, bioseparation and magnetic resonance imaging.