Ruipérez Fernando, Barandiarán Zoila, Seijo Luis
Departamento de Química, C-XIV, Universidad Autónoma de Madrid, 28049 Madrid, Spain.
J Chem Phys. 2005 Dec 22;123(24):244703. doi: 10.1063/1.2137689.
Wave-function-based ab initio calculations on the lowest states of the 4f(n),4f(n-1)5d(t2g)1, and 4f(n-1)5d(e(g))1 configurations of (LnCl6)3- clusters (Ln=Ce to Tb) embedded in the cubic elpasolite Cs2NaYCl6 have been performed, in an attempt to contribute to a comprehensive understanding of the 4f-->5d excitations of lanthanide ions in crystals. Reliable data are provided on the changes of bond lengths and breathing mode vibrational frequencies upon 4f-->5d(t2g) and 4f-->5d(e(g)) excitations, as well as on minimum-to-minimum and vertical absorption and emission transitions, and on the Stokes shifts. The available experimental data are discussed and predictions are made. The stabilization of the 4f-->5d(baricenter) excitation of the doped ions with respect to the 4f-->5d excitations of the free ions, which is a key variable for the understanding of these excitations in solid hosts, is analyzed and found to be due, in two-thirds, to dynamic ligand correlation effects and, in one-third, to orbital relaxation, charge transfer, and covalency effects present in a mean-field approximation.
对嵌入立方铯榴石Cs2NaYCl6中的(LnCl6)3-团簇（Ln = Ce到Tb）的4f(n)、4f(n - 1)5d(t2g)1和4f(n - 1)5d(e(g))1组态的最低能态进行了基于波函数的从头算计算，旨在有助于全面理解晶体中镧系离子的4f→5d激发。提供了关于4f→5d(t2g)和4f→5d(e(g))激发时键长变化和呼吸模式振动频率变化的可靠数据，以及关于最低到最低和垂直吸收与发射跃迁以及斯托克斯位移的数据。讨论了现有的实验数据并进行了预测。分析了掺杂离子的4f→5d（重心）激发相对于自由离子的4f→5d激发的稳定性，这是理解这些激发在固体基质中的关键变量，发现三分之二归因于动态配体相关效应，三分之一归因于平均场近似中存在的轨道弛豫、电荷转移和共价效应。
