科研之友
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摘要
The elementary-state electronic structure and 4f-5d transitions of Y3Al5O12:Ce3+ nanocrystals simulated by several clusters were computed by the ab initio self-consistent relativistic DV-X alpha (discrete variational X alpha) method. A 35-ion cluster was chosen to simulate the local surroundings of Ce3+ doped in Y3Al5O12 bulk crystals while four additional smaller irregular clusters were also chosen to simulate the local surroundings of Ce3+ ions in nanocrystals. Besides obtaining the elementary-state 4f and 5d electronic structure, based on the transition-state calculations we also obtained the five 4f-5d transition energies for each of these clusters. We found that compared with the bulk crystals, for all the clusters simulating nanocrystals the first 4f-5d transition peak (the lowest energy peak) was blueshifted, and the second peak was redshifted a little, which are both in accordance with the observed experimental excitation spectra of 5d luminescence of Y3Al5O12:Ce3+. We fitted the observed first two transition peaks in a published experimental excitation spectrum of nanocrystals by weighted summing of the excitation spectra of the selected clusters; therefore, the weight contribution of each cluster was obtained. Moreover, the other three unobserved peaks were all expected to be redshifted. According to these calculations and our understanding, in Y3Al5O12:Ce3+ nanocrystals, the shift of the peaks can be mainly attributed to the reduction of the crystal field felt by Ce3+ ions which results in the reduction of the splittings of 5d levels of Ce-3-as well as to the increase of the difference between the 5d average level and the 4f average level of Ce3+.
- 出版日期2011-11
- 单位中国科学技术大学
