Ce³⁺,Yb³⁺ Co-Doped Yttrium Aluminium Garnet Phosphors

How to improve the conversion efficiency of solar cells has attracted more and more attention. As crystalline Si solar cells have the band gap 1.12ev, for the ultraviolet(UV)/blue photons whose energy is much higher than the band gap, they can generate one pair of electron-hole by 1.12ev, and the rest of energy is lost through thermalization. Recently, the luminescent rare earth (RE) materials have shown potential applications in photovoltaic systems. By doping RE ions into host and using the energy transfer process between the different ions, the quantum cutting materials can realize two near-infrared phtons emitting by absorbing one UV/blue photon, and the theoretical quantum efficiency can exceed 100%. As the quantum cutting materials can modify the incident solar spectra by splitting one UV/blue photon into two near-infrared photos whose energies are more suitable for the silicon bandgap, it becomes possible that the quantum cutting materials can effectively improve the photoelectric conversion efficiency of crystalline Si solar cells.In this thesis, we investigated the fabricating process of YAG:Ce3+,Yb3+ and its luminescent emission properties. The materials were synthesized by the solid-state reaction method. The raw materials includeing four kinds of powder Al2O3, Y2O3, Yb2O3 and CeO2 were mixed well. Then these materials were moved into a furance of 1660℃ for 10h to prepare YAG:Ce3+,Yb3+ quantum cutting materials with different Yb3+ concentrations. During the period, the mixture of H2 and N2 were input to reduce the materials. X-ray diffraction was carried out to analyze the lattice properties of YAG:Ce3+,Yb3+. The emission spectra of YAG:Ce3+,Yb3+ phosphors and the fluorescent lifetime of Ce3+ were measured to analyze the energy transfer mechanism and quantum yields.The XRD patterns of YAG:Ce3+,Yb3+ shows that direct crystallization of pure-phase YAG was successfully achieved. Based on the XRD data, the lattice constant can be calculated to 1.2022 for YAG: Ce3+,Yb3+. It is very close to the lattice constant 1.2002 nm of pure YAG. This indicates that the Ce3+ and Yb3+ ions take over the position of Y3+ ions in the YAGThe energy transfer in Ce3+ and Yb3+ co-doped YAG phosphors are verified through their emission spectra of different Yb3+concentrations. Under the excitation wavelength of 450nm, the phosphors can emit the light with wavelength of around 550nm by Ce3+ and 1000nm by Yb3+. With the increase of Yb3+ concentration, the emission from Yb3+ rises, and the emission from Ce3+ decreases. The quenching concentration of Yb3+ under the excitation of 450nm is higher than that under 940nm, and the energy transfer mechanism was discussed. The measurements of fluorescence lifetimes demonstrated that the maximum quantum yields can be 163.32% for Yb3+ doping concentration of 15%.