Synthesis And Enhancement Of Near-infrared Luminescence Of Fluoride Nanoparticles Doped With Nd³⁺

In recent years,considerable researches have focused on the upconversion phosphor nanoparticles in the application of biomedical imaging which emit visible lights,nevertheless,these kinds of nanoparticles limit the light penetration depth and the imaging quality.The Nd3+ doped nanoparticles excited and emitting in the spectral range of 700-11 OOnm can overcome that shortcoming.The main researches are as follows:(1)Synthesis of small-sized NaGdF4:3%Nd3+ nanoparticles.Through controlling concentration of oleic acid,reaction temperature and reducing reaction time,small-sized nanoparticles can be achieved.NaGdF4:Nd3+ cores with an average diameter of 4.5 nm were obtained at a temperature of 280 ? for 40min with 4 mL oleic acid.The XRD data of core NaGdF4:Nd3+ nanoparticles indicates that the products are single-phase hexagonal NaGdF4 nanoparticles.(2)Improving the efficiency of NaGdF4:Nd3+ nanoparticles through homogeneous/heterogeneous shell coating.The shell thickness can be controlled by molar ratio of core and shell.The prepared nanoparticles' luminescence properties are characterized by photoluminescence spectra and fluorescence lifetimes.When excited at 808 nm,the fluorescence intensity of core/shell nanoparticles increased significantly,and the lifetimes of Nd3+ at 4F3/2 level become longer,which evidence that the shell can protect the Nd3+ ions from surface defects and improve the efficiency of NaGdF4:Nd3+nanoparticles.Notably,compared with the homogeneous NaGdF4:Nd3+@NaGdF4 nanoparticles,the fluorescence intensity of heterogeneous NaGdF4:Nd3+@NaYF4 nanoparticles enhances and the lifetimes become longer.(3)Synthesis of NaGdF4:3%Nd3+ nanoparticles with different alkali metal ions(K+?Ca2+)doped concentration.The PL intensity increased with the increase of K+ doped concentration and the lifetimes of Nd3+ at 4F3/2 level become longer.Compared with the undoped NaGdF4:Nd3+ nanoparticles with the same size,the PL intensity of NaGdF4:Nd3+ nanoparticles with K+ doped concentration of 30%doesn't exists increment,which indicates that K+ can improve the crystallinity of nanoparticles so it can help to minimize quenching sites.In addition,when Ca2+ was doped in nanoparticles with a low concentration,The PL intensity can also increase.(4)We have demonstrate that Nd3+ doped NaGdF4 nanoparticles,in addition to be excellent luminescence properties,can also be used as photo-thermal agents under 808 nm laser.It has been found that higher Nd3+ concentration lead to lager thermal effects.