Synthesis And Characterization Of Magnetic Upconversion Fluorescent Fe₃O₄/NaYF₄:Yb,Er Micro-/nano-materials

In my work, at first, series of small sized NaYF₄:Yb, Er nanoparticles （NPs） werefabricated via two thermal decomposition methods. It can be seen from TEM images thatNaYF₄:Yb, Er NPs possess uniform sizes and have very good dispersibility in cyclohexane.High bright green luminescence were observed when NaYF₄:Yb, Er NPs were under980laser.Then, to transfer these hydrophobic NPs to be hydrophilic, a very facile method wasinvestigated. Monodispersed Fe₃O₄magnetic NPs sized in¹0nm were synthesized via asimple solvothermal method. These magnetic NPs and upconversion fluorescent were readyfor fabricating Fe₃O₄/NaYF₄:Yb, Er magnetic upconversion fluorescentmicro-/nano-composites.To synthesize Fe₃O₄/NaYF₄:Yb, Er micro-/nano-composites, three fabricating strategies werestudied. They are:（1） Fe₃O₄/NaYF₄submicro-rods were synthesized via a facile hydrothermal process withthe presence of EDTA and Fe₃O₄NPs. A large number of Fe₃O₄NPs were firmly attached onthe surface of NaYF₄submicro-rods to form a hetero structure. The SP property and UCLproperty of Fe₃O₄/NaYF₄hetero-submicro-rods were studied by field-dependent magnetizationloops and luminescence spectrum, which shows their satisfied magnetization is9.4emu.g^－1which is higher than reported figures, and they emitted a bright green light under a980-nmlaser. These demonstrates that Fe₃O₄/NaYF₄submicro-rods performed obvious bifunctionalsuperparamagnetic and upconversion luminescent properties.（2） NaYF₄:Yb,Er/Fe₃O₄-SiO₂nano-composites were fabricated via a SiO₂coating method.From their TEM images we found that multiple¹0nm Fe₃O₄NPs and single NaYF₄:Yb,ErNP were coated by SiO₂layer. They possess smaller sizes and better hydrophilic, comparing with Fe₃O₄/NaYF₄submicro-rods. However, NaYF₄:Yb,Er/Fe₃O₄-SiO₂nano-composites havesome clustering, due to extra amount of SiO₂existing in the obtained samples.（3） NaYF₄:Yb,Er/Fe₃O₄nanocomposites were successfully synthesized via oil phaseevaporation method. From their TEM pictures, We found that obtained products were50nmnanocomposites which are made up of multiple10nm Fe₃O₄NPs and37nm NaYF₄:Yb,ErNPs. These small sized nanocomposites can dispersed in water, making a transparent clearsolution. Their superparamagnetic and upconversion luminescent property was clearly showedby photos. NaYF₄/Ag NPs were synthesized via the same strategy, which demonstrates that wecan fabricate other multi-functional nanocomposites via oil phase evaporation method.