Site-selective laser spectroscopy of Sm3+ ions in Y4Al2O9

Sm3+ doped Y4Al2O9 (YAM) crystals were prepared by the micro-pulling down method. Optical-absorption and laser-selective-excitation techniques along with luminescence decays have been used to reveal that Sm3+ ions in YAM normally occupy four sites, which were characterized and discussed. The comprehensive sets of Stark energy levels of the four Sm3+ centers in YAM were established. The intensity ratio of forced electric dipole (4G5/2 → 6H9/2) and magnetic dipole (4G5/2 → 6H5/2) transitions has been used to estimate the degree of asymmetry of Sm3+ sites. The lifetime of Sm3+ ions and the cross-relaxation rates were experimentally determined as a function of concentration for two distinct crystallographic Sm3+ centers. The dependencies of the nearest surroundings on the relaxation of the 4G5/2 excited state was discussed.