Synthesis Of Rare Earth Ion-Doped Core-Shell Nanostructures And Their Phonon-Dependenced Luminescence Properties

Because of the unique ability of absorb the low energy photon and emission the high energy photon, the rare earth upconversion material, it has been researched widely used in scientific. Rare earth conversion materials have wide application prospect in many aspects, so it has been researched a lot of. Its applications contains: solid state laser, display technology, especially biological imaging, biological label and photodynamic therapy fields. But the rare earth upconversion material has the problem of low efficiency. In recent years researching, core/shell structure nanoparticles(including the inert shell and the active shell) have been wide used extensively to increase the luminous efficiency. And the effect of phonon on the core/shell structure is not deeply studied. In this thesis, the NaYF4:Yb3+ Er3+ core/shell structure upconversion nanoparticles, which has different Yb3+ concentrations(including 0 concentration), is prepared by the thermal decomposition method. In this thesis, the influence of the phonon on the luminescent properties and the dynamic properties is studied. The results obtained are as follows:1. The heating rate, synthesis temperature, the properties of the matrix materials have a great influence on the synthesis of the nanoparticles.2. The ratio of 525 nm emission peak and 545 nm emission peak of NaYF4:Yb3+ Er3+ core/shell structure upconversion nanoparticles showed a monotonic decline with the increase of the temperature. And the emission spectra of 525 nm emission peaks are related to the concentration of Yb ions in the active shell. The ratio curve of the two emission peaks can be fit by exponential. This explains that the 525 nm emission peak is obtained by the thermal population. This shows that, in the NaYF4:Yb3+ Er3+ core/shell structure upconversion nanoparticles, the doping of Yb3+ in the shell increased the coupling effect between the energy and the surface defect and the environment molecules. So the level population corresponding to the 525 nm emission peak is reduced.3. The Yb3+ in the shell of the NaYF4:Yb3+ Er3+ core/shell structure upconversion nanoparticles can lead to a cross relaxation at the interface between the core and shell. And makes the NaYF4:Yb3+ Er3+ core/shell structure upconversion nanoparticles more easily affected by phonon. This phenomenon has a saturation effect. The saturation effect means that the concentration of Yb3+ in the shell is as high as 60%, the ratio of green to red is not changed with the doping concentration. This is due to the limited of the Yb3+ at the core/shell interface.4. For the NaYF4:Yb3+ Er3+ core/shell structure upconversion nanoparticles, there exists an optimum shell’s Yb3+ doping concentration. The optimum shell’s Yb3+ doping concentration obtained in this paper are 20%. Reasonable Yb3+ doping concentration is important for improving the intensity of upconversion luminescence, which plays an important role in searching and developing new ways to improve the efficiency of the upconversion.