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

Abstract

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.