Preparation And Properties Of NaYbF₄/CaS-based Rare Earth Doped Fluorescent Nanomaterials Based On Near-infrared Second Region Emissio

Compared with traditional near-infrared first-region（NIR-Ⅰ）fluorescence imaging,near-infrared second-region（NIR-Ⅱ）fluorescence imaging has higher tissue penetration and resolution.Rare-earth doped inorganic nanomaterials are defined as one of the efficient NIR-Ⅱ fluorescence imaging materials due to their excellent optical properties.Nanoparticles with smaller particle size have the characteristics of strong penetration,fast kidney filtration and fast excretion in biological systems.However,the preparation of high-brightness multifunctional small-size nanoprobe materials with good biocompatibility is still a problem and research hotspot.In this paper,a variety of new multifunctional inorganic fluorescent nanomaterials were prepared for the above problems.The details are as follows:（1）Hexagonal NaYbF₄:Tm³⁺nanoparticles were prepared by thermal decomposition method using Tm³⁺with characteristic emission at about 1470 nm as the activation center and NaYbF₄ as the host.The absorption efficiency of nanoparticles to 980 nm excitation light is increased by doping Yb³⁺.In addition,the cubic NaYbF₄:Tm³⁺nanoparticles with irregular morphology are transformed into highly monodisperse hexagonal NaYbF₄:Tm³⁺,Gd³⁺nanoparticles with controllable size by doping appropriate concentration of Gd³⁺,which reduces the nucleation and growth temperature and endows the nanoparticles with certain magnetism.Ce³⁺doping inhibits the upconversion pathway of Tm³⁺and enhances the emission intensity of the product at 1470 nm.The quenching effect is then suppressed by coating the Na YF₄ shell on the core nanoparticles.Finally,NaYbF₄:Tm³⁺,Gd³⁺,Ce³⁺@Na YF₄（NTC）nanoparticles were modified by DSPE-m PEG.After a series of tests,the final product can be used for NIR-Ⅱ bioimaging and has excellent performance.（2）The hexagonal NaYbF₄:5%Tm³⁺,30%Gd³⁺,2%Ce³⁺nanoparticles with small size and bright emission in NIR-Ⅱ were selected as the core,and the quenching effect was suppressed by coating the CaF₂ shell on the core nanoparticles.Nitrite tetrafluoroborate（NOBF₄）was used to treat the surface of the nanoparticles by ligand exchange,and then polyvinylpyrrolidone（PVP）was used to further modify the surface of the nanoparticles.After a series of tests,the final product can be used for NIR-Ⅱ bioimaging and photothermal therapy（PTT）with good results.（3）CaS:Er³⁺was synthesized by high temperature co-precipitation method.The product has small size,good monodispersity and certain NIR-Ⅱ emission intensity.By changing the amount of Er³⁺in the raw materials,the best doping concentration of Er³⁺and the best luminescence efficiency were obtained.After preliminary imaging tests,the best sample shows good near-infrared emission characteristics,and has the potential to further improve the emission intensity by co-doping Yb³⁺and Ce³⁺and apply it to bioimaging after surface modification.