Controlled Synthesis And Characterization Of Up-Conversion Micromaterials/Nanomaterials

The history of upconversion luminescence recent progress and future prospect were reviewed in this dissertation. So far, based in NaYF₄ upconversion luminescence materials is the most efficient upconversion luminescence of the conversion materials, including the hexgonal-phase crystal of up-conversion efficiency of light-emitting fluorescent materials contribute a great deal. In this work, we have successfully synthesised monodisperse hexagonal-phase NaYF₄ microprismatic via a facile solvothermal route. With second octanol as the reagent, by transmission electron microscopy and scanning electron microscopy measurements, all as-prepared samples crystallized in hexagonal microprismatic with an average length of 17μm and a diameter of about 3.4μm. The luminescence properties of hexagonal sodium gadolinium fluoride microprismatic NaYF₄, prepared using a microemulsion hydrothermal synthesis route for the first time, were evaluated following 980 nm excitation, by transmission electron microscopy and scanning electron microscopy measurements, shows the sample is hexgonal-phase microscopy NaYF₄:Yb, Er with an average length of 2.4μm and a diameter of about 1.5μm. And then we also synthesized spheric NaYF₄:Yb, Er, Tm, with an average diameter of about 98nm.Herein, the samples were characterized by XRD, FESEM, EDS, TEM, HRTEM, SAED, and so on. And we have discussed the influences of varing the molar ratio of F/Y and Na/Y, temperature and reaction time was responsible for phase control and fluorescence intensity of the NaYF₄ microprismatics. To determine the number of photons involved in the UC process of these nanocrystals, the intensities of the UC emissions are recorded as a function of the 980 nm excitation intensity density in log-log plots. Located at 410nm and 438nm are three-photon emission, both the slopes for the green and red curves at 521nm, 539nm and 654nm, respectively, which are about 2 at relatively low excitation densities, indicating a two-photon emission process. And we also discussed the detailed description about the up-conversion mechanism.