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Li ions affect the upconversion efficiency by changing the local crystal field of the luminescent center.Herein,in order to improve the upconversion efficiency of NaYF4:Yb3+/Eu3+,a series of NaYF4:Yb3+/Eu3+micro-particles with different Li+doping concentrations were synthesized by the hydrothermal synthesis method,respectively.Firstly,the structure and morphology of NaYF4:Yb3+/Eu3+upconversion micro-particles(UCMPs)with differ-ent doping concentrations were analyzed by X-ray diffraction and a scanning electron microscope(SEM).SEM results show that the UCMPs are not only highly crystallized,but also have hexagons with different Li+con-centrations of NaYF4:Yb3+/Eu3+.X-ray diffraction shows that the crystal field around Eu3+changes with the increase of Li+concentration.Then,the fluorescence spectrum of NaYF4:Yb3+/Eu3+was studied under the irradiation of a 980 nm laser.The results show that the fluorescence intensity of NaYF4:Yb3+/Eu3+with 2％Li+is the strongest,which is twice the intensity of NaYF4:Yb3+/Eu3+without Li+.Finally,the fluorescence imaging analysis of NaYF4:Yb3+/Eu3+with 2％Li+concentration was carried out.The UCMPs are used to screen printing to evaluate the imaging effect on different sample surfaces.The results show NaYF4:Yb3+/Eu3+(with 2％Li+)has great application prospects in anti-counterfeiting recognition.