Bi-functional NaLuF4:Gd3+/Yb3+/Tm3+ nanocrystals: structure controlled synthesis, near-infrared upconversion emission and tunable magnetic properties

Abstract

In this paper, fluorescent and magnetic bi-functional NaLuF₄:Ln (Ln = Gd³⁺, Yb³⁺, Tm³⁺) nanocrystals were synthesized via a simple hydrothermal method using oleic acid as capping ligand. The crystal phase, size, upconversion (UC) properties, and magnetization of the nanocrystals can be readily modified by doping with Gd³⁺. The results reveal that Gd³⁺ addition can promote the transformation from the cubic to the hexagonal phase and reduce the size. In addition, NaLuF₄:Ln (Ln = Gd³⁺, Yb³⁺, Tm³⁺) nanocrystals present efficient near infrared (NIR) to NIR emission, which is beneficial for in vivo biomedical applications due to the increased penetration depth and low radiation damage of NIR light in bio-tissues. More importantly, owing to the large magnetic moment of Gd³⁺, the Gd³⁺-doped NaLuF₄ nanocrystals also present excellent paramagnetic properties at room temperature. Therefore, it is expected that these nanocrystals can be used as promising dual-modal nanoprobes for optical bioimaging and magnetic resonance imaging (MRI), and may have potential applications in bioseparation.