Energy levels and crystal quantum states of trivalent holmium in yttrium aluminum garnet

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Abstract
Absorption spectra of Ho3+ ions in yttrium aluminum garnet (Ho3+:YAG) are reported between 2.16 and 0.23 μm at various temperatures between 4 K and room temperature. Laser-excited excitation spectra and emission spectra from the 5F4 and 5S2 multiplet manifolds to the ground state manifold 5I8 were obtained at 4, 20, and 55 K. The majority of Ho3+ ions substitute for Y3+ ions in sites of D2 point-group symmetry in the lattice. Over 1000 temperature-dependent transitions (hot bands) establish 280 experimental Stark levels of the 4 f 10(2S+1LJ) multiplet manifolds. Symmetry labels Γ1, Γ2, Γ3, or Γ4, appropriate to D2 symmetry, have been assigned to Stark levels up to 43 000 cm−1. Experimental levels are compared with results obtained from a theoretical calculation. The model Hamiltonian includes Coulombic, spin-orbit, and interconfiguration interaction terms for the 4 f 10 atomic configuration of Ho3+ and crystal-field terms in D2 symmetry. The Hamiltonian was diagonalized within the 50 lowest 2S+1LJ manifolds in a LSJMJ basis set that includes 486 calculated levels. Comparison between 151 experimental Stark levels and the corresponding levels of the lowest 199 calculated levels yields an rms deviation of 4.3 cm−1.