ENERGY-LEVELS AND UP-CONVERSION FLUORESCENCE IN TRIVALENT THULIUM-DOPED YTTRIUM SCANDIUM ALUMINUM GARNET

Absorption spectra of Tm3+ ions in Yttrium scandium aluminum garnet are reported between 1.9 and 0.25 mum at 4 K. Laser-excited fluorescence was observed at 4 K from Tm3+ (4f12) multiplet manifolds 1D2, 1G4, F-3(2), and H-3(4) to the ground-state manifold H-3(6). Emission from 1D2 and 1G4 also includes transitions to Stark levels in manifolds F-3(4) and H-3(5). Upconversion excited fluorescence was observed between 1D2 and F-3(4) at 10 K. Analysis of the fluorescence emission confirms assignments given to individual Stark levels based on an analysis of the absorption spectra. A crystal-field splitting calculation was carried out in which a parameterized Hamiltonian (including Coulombic, spin-orbit, and crystal-field terms in D2 symmetry) was diagonalized for all multiplets of the Tm3+ (4f12) configuration. The rms deviation between 42 experimental and calculated Stark levels was 8 cm-1.