Magnetic and upconverted luminescent properties of multifunctional lanthanide doped cubic KGdF4 nanocrystals

Lanthanide (Ln3+) doped KGdF4 (Ln = Yb3+, Er3+, Ho3+, Tm3+) nanocrystals with a mean diameter of approximately 12 nm were synthesized by a hydrothermal method using oleic acid as a stabilizing agent at 180 °C. The nanocrystals crystallize in the cubic phase as α-NaGdF4. When excited by a 980 nm laser, these Ln3+ doped nanocrystals exhibit multicolor up-conversion (UC) emissions in red, yellow, blue and white. The calculated color coordinates demonstrate that white UC emission (CIE-X = 0.352, CIE-Y = 0.347) can be obtained by varying the dopant concentrations in the Yb3+/Ho3+/Tm3+ triply-doped nanocrystals to yield different RGB emission intensities. The measured field dependence of magnetization (M-H curves) of the KGdF4 nanocrystals shows their paramagnetic characteristics that can be ascribed to the non-interacting localized nature of the magnetic moment of Gd3+ ions. Moreover, low temperature thermal treatment can enhance UC properties, magnetization and magnetic mass susceptibility of Ln3+ doped KGdF4 nanocrystals. The multifunctional Ln3+ doped KGdF4 nanocrystals have potential applications in color displays, bioseparation, and optical–magnetic dual modal nanoprobes in biomedical imaging.