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

Abstract

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→⁷F_J (J = 5, 4, 3, 2) and ⁵D₄→⁷F_J (J = 6, 5, 4, 3) transitions of the Tb³⁺ ions and the ⁴G_5/2→⁶H_5/2, ⁶H_7/2, ⁶H_9/2 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.