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 NaGdF 4 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 Ho 3+ in the Yb 3+ /Tm 3+ /Ho 3+ triply doped NaGdF 4 nanorods. In addition, the ultrasmall NaGdF 4 nanocrystals also exhibit paramagnetic properties at 293 K. The measured magnetizations of the NaGdF 4:20%Yb 3+ /0.2% Er 3+ and NaGdF 4 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 NaGdF 4 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 NaGdF 4 nanorods including tunable UC colors and intrinsic paramagnetic properties may have potential applications in color displays, biolables, bioseparation, and magnetic resonance imaging.