Effects of Si Codoping on Optical Properties of Ce-Doped Ca6BaP4O17: Insights from First-Principles Calculations

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• 作者：Lixin Ning ; Xiaoxiao Huang ; Jiancheng Sun ; Shizhong Huang ; Mingyue Chen ; Zhiguo Xia ; Yucheng Huang
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：February 25, 2016
• 年：2016
• 卷：120
• 期：7
• 页码：3999-4006
• 全文大小：420K
• ISSN：1932-7455

文摘

It was recently reported that Ce-doped Ca<sub>6sub>BaP<sub>4sub>O<sub>17sub> displayed blue-green emission under excitation in the near-ultraviolet (UV) region and that luminescence intensities can be greatly improved by codoping with Si. Here, a combination of hybrid density functional theory (DFT) and wave function-based CASSCF/CASPT2 calculations at the spin–orbit level has been performed on geometric and electronic structures of the material to gain insights into effects of Si codoping on its optical properties. It is found that the observed luminescence arises from 4f–5d transitions of Ce<sup>3+sup> occupying the two crystallograhically distinct Ca1 and Ca2 sites of the host compound with comparable probabilities, with the energy of the lowest 4f → 5d transition of Ce<sub>Ca1sub> being slightly higher than that of Ce<sub>ca2sub>. The codopant Si prefers to substitute for the nearest-neighbor (NN) P1 atom over the NN P2 atom around Ce<sup>3+sup>, and this preference induces a blueshift of the lowest-energy 4f → 5d transition, consistent with experimental observations. The blueshift originates from a reduction in 5d crystal field splitting of Ce<sup>3+sup> associated mainly with electronic effects of the NN Si<sub>P1sub> substitution, while the contribution from the change in 5d centroid energy is negligible. On the basis of calculated results, the energy-level diagram for the 4f ground states and the lowest 5d states of all trivalent and divalent lanthanide ions on the Ca<sup>2+sup> sites of Ca<sub>6sub>BaP<sub>4sub>O<sub>17sub> is constructed and discussed in connection with experimental findings.