ANALYSIS OF THE OPTICAL-SPECTRA OF TRIVALENT HOLMIUM IN YTTRIUM SCANDIUM GALLIUM GARNET

The absorption spectrum of Ho3+ ions in yttrium scandium gallium garnet (Ho3+:YSGG) is reported at 4 K between 1.93 and 0.28 mum. Laser excitation spectra and laser-excited fluorescence spectra from Ho3+(4f10)2S+1L(J) multiplet manifolds F-5(4), S-5(2), and F-5(3) to the ground-state manifold I-5(8) were obtained at 4, 8, and 70 K. Unresolved emission is observed from Ho3+ ions in slightly disturbed cation (Y3+) Sites along with emission coming from Ho3+ ions occupying the regular cation (Y3+) sites having D2 symmetry. Temperature-dependent transitions (hot bands) observed in absorption at 8 and 70 K establish experimental crystal-field split (Stark) levels in 24 excited manifolds and the seven lowest energy Stark levels in I-5(8) (Z1 = 0, Z2 = 6, Z3 = 17, Z4 = 29, Z5 = 87, Z6 = 95, and Z7 = 102, all in cm-1). An algorithm is used to establish D2 symmetry labels GAMMA1, GAMMA2, GAMMA3, or GAMMA4 of individual experimental Stark levels. These levels are compared with results obtained from a calculation in which a parameterized Hamiltonian was diagonalized within the 50 lowest multiplet manifolds of Ho3+ (4f10). Comparisons between 157 experimental Stark levels and the corresponding predicted levels out of a total of 486 calculated levels yields a root-mean-square deviation of 5 cm-1.