【摘要】 在Y2 O3 ∶Eu3 + 体材料和纳米材料中 ,观察到紫外激发下处于S6格位的Eu3 + 的5D0 →7F1发射 ( 5 82nm)的强度 ,相对处于C2 格位的5D0 →7F0 发射 ( 5 80nm)的强度 ,随着激发波长在 2 0 0～ 3 0 0nm紫外区由长变短而增强。这一现象说明Y2 O3 ∶Eu3 + 中两种格位的电荷迁移带及基质激发的性质不同。光谱分解得出S6格位的电荷迁移带位于C2 格位电荷迁移带的高能侧 ,Y2 O3 基质倾向于向S6格位进行能量传递。与体材料相比 ,两种格位的电荷迁移带在纳米材料中都发生红移 ;相对于C2 格位的电荷迁移带 ,S6格位的电荷迁移带强度在纳米材料中比在体材料中明显降低 ,并对结果进行了讨论。更多还原

【Abstract】 Trivalent europium-activated Y₂O₃ has attracted much attention as red emitting phosphor in commercial application on fluorescent lighting and displaying. With the development of nanotechnology, the optical properties of nanocrystalline （NC） Y₂O₃∶Eu³⁺ have also been investigated extensively for its potential application on high resolution images and for fundamental researches such as local environment probing because Eu³⁺ is supersensitive to its surroundings. As well known, Y₂O₃∶Eu³⁺ phosphor can absorb the UV light through a charge transfer band （CTB） or host excitation band and then generates red color fluorescence peaking at 611 nm. Some investigations on CTB of bulk and NC Y₂O₃∶Eu³⁺ have been reported. There exist S₆ and C₂ crystallographic sites in cubic Y₂O₃. The S₆ site has inversion symmetry center in which electric dipole transition is forbidden. Due to the absence of the inversion symmetry center, the C₂ site makes dominant contribution to the 611 nm emission which corresponds to the electronic dipole transition of （）⁵D₀→⁷F₂ in Y₂O₃∶Eu³⁺. Hence, the generally observed CTB and host excitation band in the excitation spectra by monitoring the red color fluorescence from （）⁵D₀→⁷F₂ transition merely corresponds to the C₂ site. Although the S₆ site has almost no contribution to the red color fluorescence, it possibly competes with the C₂ site for energies under UV excitation. To our knowledge, there is no report on the UV excitation properties of the S₆ site in bulk and nanocrystalline Y₂O₃∶Eu³⁺. The S₆ site allows the magnetic dipole transition （）⁵D₀→⁷F₁ of Eu³⁺, which provides the possibility to study the UV excitation properties of the S₆ site. The CTB and host excitation band for Eu³⁺ at the S₆ site in bulk and nanocrystalline Y₂O₃∶Eu³⁺ is mainly investigated. The NC （Y₂O₃∶）0 01 Eu³⁺ was prepared by fast thermal decomposition of metal nitrate solution. The advantage of this method is that pure cubic phased Y₂O₃∶Eu³⁺ nanocrystals can be obtained at a relatively lower temperature than by any other methods. The particle sizes were determined to be 7 nm from a survey of the transmission electron microscopy micrographs. The bulk Y₂O₃∶0 01 Eu³⁺ powders was formed by annealing as-prepared corresponding nanoparticles at （1 250） ℃ in air. It was determined to be 2～3 μm by field-emission scanning electron microscopy （FE-SEM）. Both the samples were identified as cubic structure from XRD. The spectra were carried out at room temperature with a Hitachi F-4500 florescence spectrometer using a Xe lamp as the excitation source. Increases of emission intensities for Eu³⁺ at the S₆ site relative to that at the C₂ site have been observed as UV excitation wavelength decreases from 200 ～ 300 nm in both bulk and nanocrystalline cubic (Y₂O₃∶Eu³⁺.) It indicates that the two kinds of sites have different charge transfer states and host lattice excitation responds. Decomposition of excitation spectra shows that the charge transfer band（CTB） of Eu³⁺ at the S₆ site is located at the high-energy side of the C₂ site and the host prefers transferring energy to the S₆ site. Compared with the bulk material, the CTBs for the two sites both shift toward the red and the number ratio of S₆ to C₂ sites is smaller in nanocrystalline Y₂O₃∶Eu³⁺. Above results are discussed.更多还原