MULTISITE OPTICAL-SPECTRA AND ENERGY-LEVELS OF TRIVALENT THULIUM IONSIN YTTRIUM SCANDIUM GALLIUM GARNET

Intrinsic structural disorder in scandium-substituted garnets, attribu ted to mixed occupancy o certain sites in the crystal lattice by diffe rent cations, has direct consequences for the optical spectra of rare- earth activator ions dispersed over multiple sites. In trivalent thuli um-doped yttrium scandium gallium garnet (Tm3+:YSGG), site-selective l aser excitation spectra reveal the presence of Tm3+ ions in regular D2 sites, disturbed regular sites, and in octahedral C3i sites. Absorpti on spectra obtained at 4 K between 0.26 and 1.85 mum are broader than those observed in more-ordered crystal hosts and include structure att ributed to Tm3+ ions in sites of other than D2 symmetry. A crystal-fie ld splitting calculation was carried out in which a parametrized Hamil tonian (including Coulombic, spin-orbit, and crystal-field terms for T m3+ ions in D2 symmetry) was diagonalized for all manifolds of the Tm3 + (4f12) configuration. The rms deviation between 52 experimental and calculated Stark levels of Tm3+ in regular D2 sites was 5 cm-1.