Core-shell Structured Upconversion Nanocomposites:Synthesis,Tuning Of Luminescent Properties,and Anticancer Study

Because of the small size and high surface area,nanoparticles possess speciall physical and chemical properties,which provide them enormous potential in the fields of laser,biomedicine,catalysis,sensing and environmental technology.Along with the development of the applications,the requirement of structure,function,size and composite for nanomaterials is urgent.And the single function of pure materials can not satisfy the needs already.So,functional materials come into being,and studied widely.Herein,we designed several luminescent and/or magnetic nanocomposites with core-shell structures,because the combined functionalities of cores and shells endow them with great potential application in various fields.And we synthesized three kinds of core-shell structure nanocomposites.In the first part,monodisperse,regular-shaped and well-crystalline NaGdF4:Yb3+/Er3+@NaLaF4 nanocrystals(NCs)with diverse shapes and structures have been successfully prepared using oleic acid(OA)and 1-octadecene as high boiling solvents via a competitive nucleation and growth pathway.The phase,morphology,structure,and photoluminescence properties of the as-synthesized NCs are well characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),high resolution transmission electron microscopy(HRTEM),Fourier transform infrared spectroscopy(FT-IR),and photoluminescence(PL)spectra,respectively.The as-synthesized NCs can easily be dispersed in non-polar cyclohexane solvent for their hydrophobic surface.Under a single 980 nm NIR excitation,Yb/Er,Yb/Tm and Yb/Ho co-doped NaGdF4 NCs show the characteristic up-conversion(UC)emissions of Er3+,Tm3+ and Ho3+,respectively.It is important that the size,high dispersity and UC luminescence of the converted hydrophilic NCs can be maintained,suggesting its potential application in the fields of biolabel,bioimaging,and other optical technologies.Then,we report for the first time the synthesis of monodisperse,magnetic and up-conversion luminescent Fe3O4@NaGdF4:Yb/Er@NaGdF4:Yb/Er core-shell structured nanoparticles(NPs)by a seed-growth process.The growth of a NaGdF4:Yb/Er shell on Fe3O4@NaGdF4:Yb/Er NPs can significantly enhance the upconversion emission intensity.In the third part,we for the first time proposed a self-produced bubble-template synthesis of La2O3:Yb/Er hollow mesoporous spheres(HMSs)through a facile one-step co-precipitation process.The temperature which decides the bubble formation and citric acid/NaOH which determine the dispersibility are the main factors to the formation of La2O3:Yb/Er HMSs.Au nanocrystals(NCs)with the particle size of 9 nm were conjugated to the as-prepared La2O3:Yb/Er HMSs without adding any organic reagents.It is noted that the up-conversion(UC)luminescence intensity of La2O3:Yb/Er@Au was markedly improved by 49.7-fold under low pump power.Doxorubicin(DOX)release property,and obvious cytotoxicity to MCF-7 tumor cells,revealing the potential application as drug carrier.In particular,the facile and mass-production synthetic strategy may pave the way for the production of a wide class of materials.