Excited-state absorption spectra of V2+-doped fluoroperovskites. An ab initio model potential embedded-cluster study

In this paper we present an ab initio model potential embedded-cluster study of the electronic structure of the local excited states of V2+-doped KMgF3, KZnF3, and CsCaF3 fluoroperovskites, which are more directly involved in their potential laser activity: the T-4(2g), T-4(1g)a, and T-4(1g)b, states of the (VF6)(4-) embedded-cluster. The ab initio model potential embedded-cluster model used allows for the consideration of intracluster electron correlation and Jahn-Teller coupling in the excited states, as well as of lattice effects which include quantum mechanical interactions resulting from a relaxed, dipole polarized crystal lattice. The embedding potentials enable the geometry optimization of the embedded-cluster electronic ground-state but also of the excited states; as a consequence, the ab initio calculation of the vertical ground-state absorption, excited-state absorption, and emission spectra is possible and it is done in this work, without resorting to the use of experimental structural parameters of the local defect, which, in any case, are not available for the ground state and not attainable for the excited states. The agreement of the calculated ground-state absorption, excited-state absorption, and emission transition energies with the available experimental data is satisfactory and systematic. Our results allow for the discussion of (a) the competition between the infrared T-4(2g)-->T-4(1g)a, excited-state absorption and the T-4(2g)-->(4)A(2g) spontaneous emission, (b) the overlap between the excited-state absorption bands and the pumping bands, and (c) the (4)A(2g)-->T-4(2g) reabsorption, for all three V2+-doped fluoroperovskites, as well as their host dependency. The overall conclusion is that the laser efficiency is expected to deteriorate in the investigated series, going from KMgF3:V2+ to CsCaF3:V2+. (C) 1996 American Institute of Physics.