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

Tb3+ and/or Sm3+ 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 Tb3+ or Sm3+ doped samples show strong green and yellow emission, originating from the allowed 5D3→7FJ (J = 5, 4, 3, 2) and 5D4→7FJ (J = 6, 5, 4, 3) transitions of the Tb3+ ions and the 4G5/2→6H5/2, 6H7/2, 6H9/2 transition of the Sm3+ ions. Based on the excitation wavelengths, multiple (yellowish green, yellow, white) emissions are obtained by Sm3+ ion co-activated NaGdF4:Tb3+ phosphors. Moreover, an energy transfer from Tb3+ to Sm3+ is observed, which is justified through the luminescence spectra and the fluorescence decay curves. Furthermore, the resonance-type energy transfer from Tb3+ to Sm3+ 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 Tb3+, Sm3+ 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.