Investigations On Multi-functional NaLnF₄（Ln=Er,Lu） Nanocrystals: Structure Controlled Synthesis, Tunable Luminescence And Magnetic Properties

In recent years, lanthanide(Ln) doped rare-earth compound nanomaterials has extensive application prospect in the fields of electronics, color displays, optical devices and especially biomedical imaging because of their excellent physical and chemical properties. Due to their low phonon energy, high transmittance and good stability, fluorides(NaLnF4) have been extensively investigated within all of the investigated host materials. Rare-earth upconversion fluorescent nanomaterials are fresh fluorescent probe materials, which can absorb longer wavelength and emit high-energy short wavelength photon. Thus, the upconversion nanomaterials have many special advantages in biological imaging, which include low radiation damage, weak auto-fluorescence and strong penetration. More importantly, apart from upconversion fluorescence property, a lot of Ln-doped rare-earth compounds also have intrinsic magnetic property, which can make this kind of nanomaterials have optical/magnetic dual-modal imaging property. Although it have excellent optical and magnetic properties, and there still exist a lot of unresolved key issues to be solved at present, including the enhancement of upconversion fluorescent efficiency, the controlled synthesis of nanomaterials morphology and size, the adjustment of upconversion fluorescence and magnetism, and multi-modal imaging, etc. A research of the controlled synthesis and tuned optical/magnetic properties of multi-model NaLnF4(Ln=Er, Lu) nanocrystals have proposed in this work. The main conclusions are as follows:1. The high quality optical/magnetic dual-functional NaErF4 nanocrystals with different phase and morphology were synthesized by a mild hydrothermal method. By adjusting reaction condition(the reaction temperature and NaF content), different shape, size and phase of the nanocrystals were obtained. In addition, the phase and shape induced upconversion fluorescence color and magnetization tuning were also studied. Moreover, the multi-functional NaErF4 nanomaterials can used as T2 weighted magnetic resonance imaging contrast agent.2. The monodisperse Mn2+ doped NaErF4:Yb nanoparticles were successfully synthesized through a solvothermal method. In addition, the morphology, crystalline phase and upconversion luminescence properties of the NaErF4:Yb nanomaterials doped with different Mn2+ concentration(0%, 5%, 20% and 30%) were investigated.The results reveal that Mn2+ doping can simultaneously control the crystalline phase, size and morphology of NaEr F4:Yb nanocrystals. The Mn2+ doping can also influence the upconversion luminescence properties of the products. Furthermore, by Mn2+ doping the red to green ratio(R/G) of the NaErF4:Yb increased from 19 to 367. In addition, the brighter luminescence intensity of NaErF4:Yb, 30% Mn can be achieved by Mn2+ doping. The single-band red emission of NaErF4:Yb, 30% Mn nanomaterials is 2.3 times brighter than that of NaErF4:Yb.3. The multi-functional pure hexagonal phase NaLuF4:Gd/Yb/Er nanorods were synthesized by a hydrothermal method through doping Gd3+. The results show that the method of Gd3+ doping can controlled size and crystal phase of NaLu F4:Gd/Yb/Er nanomaterials. The tunable crystalline phase, shape and size of the nanorods can be realized by Gd3+ doping, from small cubic phase to larger hexagonal phase. More importantly,the magnetic property can be induced by Gd3+ doping.