Luminescence spectroscopy of matrix-isolated atomic manganese: Excitation of the "forbidden" a(6)D(J)<-> a(6)S transitions

International audienceLaser-induced excitation spectra recorded for the electric-quadrupole 3d(6)4s a(6)D(J) a(6)S(5/2) transition at 585.75 nm. The identified matrix-shift of +20 cm(-1) allows an assessment of the extent of the ground state stabilization in the red (2 degrees) site of atomic Mn isolation in solid Kr. Emission produced with direct a(6)D state excitation yielded both the 585.75 and 626 nm features. The former band arises for Mn atoms occupying the red site-the latter from blue site occupancy in solid Kr. The excitation linewidths recorded for these two sites differ greatly, with the blue site yielding a broad featureless profile, in contrast to the narrow, structured features of the red site. The corresponding red site a(6)D(J) a(6)S(5/2) transitions in Ar and Xe matrices are broader than in Kr-a difference considered to originate from the site sizes available in these hosts and the interatomic Mn center dot RG potentials. The millisecond decay times recorded for the red emission bands in the Mn/RG systems are all much shorter than the 3 s value predicted for the gas phase a(6)D(9/2)-> a(6)S(5/2) transition. This enhancement allows optical pumping of the forbidden a(6)D(J) a(6)S transitions with low laser powers when atomic manganese is isolated in the solid state. However all the emission decays are complex, exhibiting triple exponential decays. This behavior may be related to the dependence of the excitation linewidths on the J value, indicating removal of the J degeneracy due to weak matrix-induced, crystal field splitting