Cr3+ centers in the LaMgAl11O19 laser host: theoretical study through a molecular orbital model

The electronic structures of Cr-Cr pair centers at 4f sites detected in fluorescence and absorption studies of LaMgAl11O19 crystal doped with Cr3+ are studied. A molecular orbital model using the spin polarized option of the SCF X alpha method is used. Eigenvalues of 02p, Cr3d and Al3s, Al3p in various clusters representative of undoped and doped 2a, 4f and coupled 4f sites in LaMgAl11O19 are presented. For the 4f site, the 2E→ 4A2 emission line is calculated to be 0.075 eV lower than in the 2a case. The evolution of the calculated 2E and 4T2 energies shows that 2a, 4f and pair centers behave as more and more low-field chromium complexes in the region Dq/B∼ 2 in the Tanabe and Sugnao d3 diagram