Ab Initio Calculation of Electronic Structure and 4f–5d Transition Energies of Ce3+ Doped in Y3Al5O12 Nanocrystals
Abstract: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-Xα (discrete variational Xα) 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 Ce3—as well as to the increase of the difference between the 5d average level and the 4f average level of Ce3+.
Document Type: Research Article
Publication date: November 1, 2011
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