Sharp Lines Due to Cr3+ and Mn2+ Impurities in Insulators: Going Beyond the Usual Tanabe鈥揝ugano Approach

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• 作者：J. M. Garc铆a-Lastra ; P. Garc铆a-Fern谩ndez ; M. T. Barriuso ; J. A. Aramburu ; M. Moreno
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：March 27, 2014
• 年：2014
• 卷：118
• 期：12
• 页码：2377-2384
• 全文大小：317K
• 年卷期：v.118,no.12(March 27, 2014)
• ISSN：1520-5215

文摘

This work is aimed at understanding the different behavior of optical sharp lines (corresponding to 10Dq-independent transitions) of Mn²⁺ and Cr³⁺ in normal and inverted perovskites that cannot be explained within the usual Tanabe-Sugano approach. In particular, we want to clarify why on passing from KMgF₃:M to LiBaF₃:M (M = Mn²⁺, Cr³⁺) the energy, E(⁶A₁ 鈫?⁴A₁), for Mn²⁺ decreases by 螖 = 1100 cm^鈥?, while 螖 < 100 cm^鈥? for the energy E(²E 鈫?sup>聽4A₂) corresponding to Cr³⁺. The origin of this surprising difference in these model systems is clarified by writing the transition energies of MF₆ complexes through the ten Coulomb and exchange integrals consistent with the cubic symmetry and not considered in the usual Tanabe鈥揝ugano approach. It is shown that E(⁶A₁ 鈫?⁴A₁) depends on exchange integrals K(3z² 鈥?r², xy) and K(x² 鈥?y², xy), while E(²E 鈫?⁴A₂) depends on K(xz, yz) where the two involved electrons display a 蟺 character. These exchange integrals have been calculated just considering a MF₆ unit subject to the internal electric field due to the rest of the lattice ions. In addition to a reasonably reproduction of the main trends observed experimentally for the model systems, the present calculations prove that the exchange integrals are not related in a simple way to the covalency of involved orbitals. Particular attention is also paid to explain why the transitions, which are 10Dq-independent are less sensitive to the host lattice change than those which do depend on 10Dq. The present work shows that K(xz, yz) for Cr³⁺ is particularly insensitive to the host lattice change and thus sheds light on the origin of the near independence of E(²E 鈫?⁴A₂) along the series of oxides doped with such an impurity .