The Preparation And Upconversion Luminescent Properties Of NaScF₄:Yb,Er Upconversion Nanomaterials

During the past decade,the rare earth upconversion nanocrystals have gradually attracted the attention of researchers,due to their applications in the fields of biosensing,biological imaging,photodynamic therapy,optical storage and 3D display,security and so on.Its main advantages lie in:1)morphology and size of rare earth upconversion nanocrystals can be controlled by different synthesis methods,adapt to the requirements of rare earth nanoparticles in various fields;2)upconversion nanocrystals can absorb near-infrared light,the energy of near-infrared light could be less damage to the biological tissue;3)upconversion fluorescence emission can achieve controlled emission wavelength and emission intensity by doping different activator,altering the concentration of dopants or tuning nanoparticle size.At present,the research on the host materials of rare earth nanomaterials primarily focus on NaLnF4(Ln = La-Lu,Y)nanocrystals.Scandium is the rare earth element and transition element,to the best of our knowledge,studies of the synthesis and optical properties of inorganic compound of scandium is still rare.However,as for indispensable RE element,scandium behaves comparatively distinct electronic structures and small radius,which may produce unique optical properties.In this paper,by adjusting the polarity of the reaction medium,we obtained different sizes of NaScF4:Yb,Er nanoparticles,we study size-dependence of upconversion luminescence in Yb3+/Er3+ doped NaScF4 host.Finally,based on heterostructure of core-shell,the upconversion luminescence emission can be controlled by different synthesis methods.It mainly includes following several partial contents:1.We reported the multicolour emission of NaScF4:Yb,Er(Tm)upconversion nanoparticles,which are synthesized by thermal co-precipitation,doped with different rare-earth ions and possess different sizes,and finally the nanoparticles can be tuned by different colors.At the same time,we study the properties of NaScF4 with different doped ions,and we prove the energy transfer between sensitizers and activitors,and in the end,we can obtain different emission colors.2.We reported the synthesis of different size and morphology NaScF4:Yb,Er nanocrystals with hot coprecipitation method by tuning the ratio of oleic acid(OA)and 1-octadecene(ODE).The upconversion luminescence of NaScF4:Yb,Er nanoparticles,including the decay time,green red ratio,and the temperature response with different sizes,are further investigated.Finally,a potential application of these materials as fluorescent thermometer is demonstrated.3.We reported improved the intensity of luminescence emission by homoepitaxial core-shell NaScF4:Yb,Er@NaScF4 nanostructures.The previous prepared NaYF4:Yb,Er upconversion nanocrystals as core by thermal co-precipitation,the precursor Sc-OA reacts with the Na-TFA-OA precursor to produce NaScF4 as shell by successive layer by layer method.More interestingly,the thickness of shell and the intensity of upconversion emission can be adjusted the concentration of shell precursor.