MULTIPLE-EXCITED-STATE ABSORPTION OF V2-FIELD CRYSTALS - AN AB-INITIOMODEL-POTENTIAL EMBEDDED-CLUSTER STUDY( IN LOW)

In this paper we present an ab initio model-potential embedded-cluster study of the spin doublet excited states of V2+-doped KMgF3, KZnF3, a nd CsCaF3 fluoroperovskites, which includes intracluster electron corr elation and quantum-mechanical lattice effects. The discrepancies of t he calculated ground-state absorptions to the spin doublets with avail able experiments are systematic and amount to some 1000 cm(-1), leavin g room for improvement of the treatment of valence electron correlatio n. The calculated excited-state absorption spectra originating in E-2( g) and T-2(1g) show that the broad E-2(g), T-2(1g)-->(2)A(1g) absorpti on bands considerably overlap the potential T-4(2g)-->(4)A(2g) laser e mission, thus establishing a mechanism for laser loss that had not bee n considered so far in these low-field materials. The results obtained in these V2+-doped fluoroperovskites, together with those in other d( 3)-doped low-field crystals, point out that the observed excited-state absorption spectra may correspond to either a single absorbing excite d state or to the superposition of electronic transitions originating in all the different stable excited states lying below the energies us ed for pumping. Each of these excited states becomes a channel for abs orptions that may result in multiple laser loss mechanisms. The separa te study of each of these channels appears to be feasible using ab ini tio embedded-cluster methods. The conditions for the occurrence of sin gle (T-4(2g)) versus multiple (T-4(2g), E-2(g), T-2(1g)) excited-state absorption, and, therefore, single versus multiple loss mechanisms, a re discussed in this paper in terms of the energy barrier to E-2(g), T -2(1g)-->T-4(2g) nonradiative decay. [S0163-1829(98)08019-9].