Most of the ${}^{2S+1}L_J$ multiplets of the ${\mathrm{Nd}}^{3+}$ ion $\left(4f^3\right)$ in ${\mathrm{Bi}}_4{\mathrm{Ge}}_3{\mathrm{O}}_{12}$ and ${\mathrm{Bi}}_4{\mathrm{Si}}_3{\mathrm{O}}_{12}$ single crystals have been experimentally observed in the UV, visible, and NIR spectroscopic regions. The majority of the Stark energy levels were identified for each multiplet, including some recently identified. In these crystals, the ${\mathrm{Nd}}^{3+}$ ions substitute ${\mathrm{Bi}}^{3+}$ ions at sites of $C_3$ point group symmetry. A Hamiltonian including the Coulomb, spin-orbit, interconfigurational interaction terms of the ${\mathrm{Nd}}^{3+}\left(4f^3\right)$ configuration, and trigonal crystal-field terms was used to fit these energy levels. The Hamiltonian was diagonalized in the $\mid {\mathrm{SLJM}}_J⟩$ complete $4f^3$ basis that includes 364 states. A least-squares fit was carried out for all the observed energy levels. Previously obtained $B_{kq}$ crystal-field parameters did not reproduce all of the observed ${\mathrm{Nd}}^{3+}$ energy levels. The $B_{kq}$ parameters obtained in this work allow a good energy level fitting for both lattices. The obtained crystal-field parameters produced an average standard deviation of about $20{\mathrm{cm}}^{-1}$. Although the intensity of the crystal field experimented by the neodymium ions in both lattices is quite similar, an analysis of the nephelauxetic ratio shows a larger wave-function overlap in bismuth silicate than in bismuth germanate. Also, the spectroscopic electron paramagnetic resonance Landé $g$ factors were calculated for both lattices, obtaining excellent agreement with the experimental values.

• Received 2 June 2006

DOI:https://doi.org/10.1103/PhysRevB.75.125405