Preparation Of NaErF₄:Ce³⁺ Rare Earth-doped Nanocrystals And Study Of Its Near-infrared Luminescence Properties

As an emerging technology,the fluorescent probes in the second near infrared window(1000-1700nm)have attracted widespread attention.Compared with the traditional probes in the visible range(400-700nm)and in the first near infrared window(700-900nm),the probes in the second near infrared window,which provide higher signal-to-noise ratio and deeper penetration,have greater potential in disease detection and treatment.Among the existing luminescent materials in the second near infrared window,the rare-earth doped nanocrystals have the advantages of good light stability,low biotoxicity,narrow emission band,low photobleaching rate and long fluorescence lifetime,etc.Therefore,they are one of the best choices for the fluorescent probes in the second near infrared window.In this paper,the "non-doped" rare-earth nanocrystals NaErF4@NaYF4 with strong luminescence in the second near infrared window were synthesized via Ostwald ripening method.In order to improve their biocompatibility,two surface modification methods were used to produce water-soluble nanocrystals.In addition,the biocompatibility and light stability were verified by cell experiments.The main contents of this paper are as follows:(1)Controlled synthesis of rare-earth doped nanocrystals.The monodispersed hexagonal-phase core-shell nanocrystals with uniform size distribution and good crystallinity were successfully synthesized by thermal decomposition method.X-ray diffractometer(XRD),Transmission electron microscope(TEM),Dynamic light scattering granulometer(DLS)and some other testing methods were used to characterize the phase,morphology and size of the nanocrystals.(2)Studies on fluorescence properties of rare-earth doped nanocrystals.By measuring and analyzing the fluorescence performance of NaErF4:x%Ce3+@NaYF4(x=0,0.1,0.5,1,2,3,4,5,7,10)nanocrystals,it was found that the luminous intensity of the nanocrystals in the second near infrared window was significantly improved by a certain amount of Ce3+doping.The luminescence mechanism and energy transfer of the nanocrystals were analyzed.(3)Studies on surface modification of rare-earth doped nanocrystals.The surface of nanocrystals was modified by two methods:silica coating and lipid polymer coating.By means of TEM,DLS,zeta and fluorescence characteristics,the modification effects of the two-methods were analyzed.(4)Verification of the biocompatibility of nanocrystals.Through cytotoxicity experiments and cell phagocytosis experiments,it was verified that the low-biotoxicity nanocrystals have successfully entered the cells and kept good luminescence properties.