Investigation On Controllable Synthesis And Upconversion Luminescence Of NaGdF₄:Er³⁺,Yb³⁺

Due to unique optical properties, rare earth doped up-conversion(UC) luminescent materials have profound applications prospects in the fields such as integrated optics, solar cells, biomedical imaging. It finds that the luminescent properties have close relationships with the morphology, size and crystal structure of the UC materials in the previous research. Therefore, the controllable synthesis of UC materials is of great practical significance to the expansion of its application. Herein, this paper chose NaGdF4as host material,and used the solvothermal method as the basic approach to synthesize the UCNPs. By changing the reaction temperature, dosage of chelating agent or the doping concentration of Yb3+series of NaGdF4:Er3+,Yb3+which had different morphology and size were synthesized. Furthermore, the effects of these synthesis conditions on the final products were also investigated. The main results are as follows:A series of β-NaGdF4:Er3+,Yb3+UCNPs whose sizes between7-15nm but with strong luminosity were synthesized by changing the synthesis temperature. The XRD and TEM images showed morphology, size and structure, the UC spectra of different β-NaGdF4:Er3+,Yb3+nanocrystals were also measured.About all, the effects of temperature on the properties of final products were investigated, the result indicates that along with the increase of the solvothermal-treatment temperature, the size, crystallinity, and luminescence intensity of the sample increase. While, opposite size dependences of the red/green UC luminescence intensity ratio were observed for the UC luminescence in different surface condition(dry and moisture-adsorbed)We studied the influence of the dosage of chelating agent(sodium citrate) on the various performance ofβ-NaGdF4:Er3+,Yb3T UCNPs. The result shows that: the higher the Cit/RE ratio is, the better the dispersity, crystallinity and luminescence intensity of the UCNPs are, and the more like a regular sphericity looks. Besides, by comparing the power curves of different samples, we found that the dosage of chelating agent (sodium citrate) can affect the UC mechanism of the sample’s red and green UC luminescence.We changed the doping concentration of Yb3+to synthesize a series of β-NaGdF4:Er3+,Yb3+nanocrystallines which have a large change in size (10nm-160nm). The characterization of whose properties shows that: Along with the increase of doping concentration of Yb3+, the size, luminescence intensity and luminescence efficiency of the sample increase, too.We also found that the red/green luminescence intensity ratio of the sample demonstrates step-wise rising with the increase of the doping concentration of Yb3+, which also influences theup-conversion mechanism of the red and green UC luminescence.