Covalent mechanism of cooperative optical transitions in lanthanide exchange-coupled pairs. Intensity calculations for double transitions in a M(2)L(11) f(1)-f(1) dimer

The covalent mechanism of cooperative optical transitions in exchange-coupled pairs of lanthanide ions (which is closely related to the magnetic superexchange mechanism) is analyzed in detail for a simple M(2)L(11) f(1)-f(1) model dimer (two ML(6) octahedra sharing one bridging ligand L). New effective electron transfer pathways in the M(A)-L-M(B) exchange system are considered and intensities of cooperative transitions from the (00) ground state to (ij) doubly-excited states of the f(1)-f(1) dimer are calculated including polarization effects.