EXCITED-STATE PROPERTIES OF CR3- A DENSITY-FUNCTIONAL STUDY( IN CS2NAYCL6 AND CS2NAYBR6 )

The ground and excited state properties of the Cr3+ ion doped into the cubic host lattices Cs2NaYCl6 and Cs2NaYBr6 have been studied using d ensity functional theory. A new symmetry based technique was employed to calculate the energies of the multiplets (4)A(2g), T-4(2g), (2)E(g) , and T-4(1g). The geometry of the CrX(6)(3-) cluster was optimized i n the ground and excited states, A Madelung correction was introduced to take account of the electrostatic effects of the lattice. The exper imental Cr-X distance in the ground state can be reproduced to within 0.01 Angstrom for both chloride and bromide systems. The calculated d- d excitation energies are typically 2000-3000 cm(-1) too low. An energ y lowering is obtained in the first T-4(2g) excited state when the oct ahedral symmetry of CrX(6)(3-) is relaxed along the e(g) Jahn-Teller c oordinate. The geometry corresponding to the energy minimum is in exce llent agreement with the T-4(2g) geometry derived from high-resolution optical spectroscopy of Cs2NaYCl6:Cr3+. It corresponds to an axially compressed and equatorially elongated CrX(6)(3-)-octahedron. (C) 1996 American Institute of Physics.