Ce³⁺-Tb³⁺-Yb³⁺ Co-Doped Yttrium Aluminium Garnet Phosphors

Solar energy, as a type of inexhaustible, clean, safe and renewable energy, has attracted more and more attentions. However, solar cell are too expensive to be used widely, owing to low power conversion efficiencies. One of the reasons is that crystalline Si solar cells, with the band gap of 1.12ev, absorb one ultraviolet/blue photon whose energy is much more than the band gap, and then generate one pair of electron-hole accompanying with carriers thermalization. In rencent years, luminescent rare earth (RE) downconversion materials, which are capable of converting one ultraviolet/blue photon to two or more near-infrared photons whose energy matches well with the Si solar cells have been synthesized and used to minimize the carrier thermalization.In this thesis, the energy transferring mechanism in Ce3+-Tb3+-Yb3+ tri-doped yttrium aluminium garnet (YAG) phosphors energy transferring efficiency and the Tb3+ quenching concentration are investigated. The materials were synthesized by the solid-state reaction method. X-ray diffition (XRD) test was conducted to analyse the lattice structure of Ce3+-Tb3+-Yb3+ tri-doped YAG phosphors. The excitation and emission spectra of Ce3+-Tb3+-Yb3+ tri-doped YAG and the fluorescent lifetime of Ce3+ and Tb3+ were measured to analyse the energy transferring mechanism and the Tb3+ quenching concentration. The XRD patterns of Ce3+-Tb3+-Yb3+ tri-doped YAG shows that direct crystallization of YAG was achieved successfully. The calculated lattice constant is 1.2009nm which is very close to the pure YAG. This indicates that the Ce3+, Tb3+ and Yb3+ take over the positions of Y3+ in YAG.The energy transferring efficiency results which are calculated from the fluorescent lifetime of Ce3+ and Tb3+ show that the energy transfers from Tb3+ to Ce3+ and from Ce3+to Yb3+ are efficient while the energy transfers from Ce3+ to Tb3+ and from Tb3+ to Yb3+ are inefficient. Meanwhile in Ce3+-Tb3+-Yb3+ tri-doped YAG, Yb3+ receives mainly energy from Ce3+. The emission spectra of the different Tb3+ ion concentration in the tri-doped YAG phosphors indicates that the Tb3+ ions quenching concentration is 15%.