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Photoluminescence Properties of CeO 2 :Eu 3+ Nanoparticles Synthesized by a Sol-Gel Method

2008; American Chemical Society; Volume: 113; Issue: 2 Linguagem: Inglês

10.1021/jp808688w

1932-7455

Ling Li, Hyun Kyoung Yang, Byung Kee Moon, Zuoling Fu, Chongfeng Guo, Jung Hyun Jeong, Soung Soo Yi, Kiwan Jang, Ho Sueb Lee,

Gas Sensing Nanomaterials and Sensors

Nanocrystalline Eu3+-doped CeO2, CeO2, Sm3+-doped CeO2, and Li+, Eu3+-codoped CeO2 samples were prepared through a sol−gel process. The structure and the optical properties of the samples were characterized by X-ray diffraction, diffuse reflection spectra, and photoluminescence spectra. No luminescence was observed for nanocrystalline CeO2. The systematic investigation shows that the broad band in the excitation spectrum of CeO2:Eu3+ comes from the charge transfer (CT) transition from O2− to Ce4+, not from the oxygen vacancy, or from the CT of O2− to Eu3+. Upon increasing the fired temperature from 600 to 800 °C, the excitation spectrum shifts to lower energy. With increasing concentrations of Eu3+ up to 1% in CeO2, red shifts of the excitation spectra are observed; however, when the concentration of Eu3+ increases to 5% and 10%, blue shifts occur. The emission spectrum shows that the symmetry of the Eu3+ site becomes lower with increasing Eu3+. Based on the dielectric theory of complex crystals, the environmental factor (he) and the dielectric definition of average energy gap around the centers of Eu3+ are calculated. The reasons for the shifts of the excitation spectra are discussed in detail.