Tunable multicolor upconversion emissions and paramagnetic property of monodispersed bifunctional lanthanide-doped NaGdF₄ nanorods

In this paper, highly monodispsered ultrasmall hexagonal phase NaGdF 4 nanorods were synthesized via a hydrothermal method using oleic acid as a stabilizing agent. The tunable multicolor upconversion (UC) emissions, including green, yellow, blue, and white emissions, can be readily achieved from lanthanide (Ln)-doped NaGdF4 nanorods under the excitation of a 980 nm diode laser. The calculated chromaticity coordinates (CIE-X = 0.346, CIE-Y = 0.357) are close to those of the standard white light (CIE-X = 0.33, CIE-Y = 0.33), and the white UC emissions can be tuned from blue-white to white by adjusting the doped contents of Ho3+ in the Yb3+/ Tm3+/Ho3+ triply doped NaGdF4 nanorods. In addition, the ultrasmall NaGdF4 nanocrystals also exhibit paramagnetic properties at 293 K. The measured magnetizations of the NaGdF 4:20%Yb3+/0.2% Er3+ and NaGdF4 nanocrystals were about 1.49 and 1.86 emu/g at 20 kOe, respectively, which were close to the reported values of other nanoparticles for bioseparation. Moreover, the NaGdF4 nanocrystals can be readily attracted by a small magnet, which shows it has potential application in cell isolating. It is expected that these multifunctional ultrasmall NaGdF4 nanorods including tunable UC colors and intrinsic paramagnetic properties may have potential applications in color displays, biolables, bioseparation, and magnetic resonance imaging.