Crystal field analysis of Nd3+ energy levels in monoclinic NdAl3(BO3)4 laser

The energies of 135 Kramers doublets extending up to the (2)H1(11/2) multiplet for Nd3+ in a monoclinic C2/c space group (No 15) NdAl3(BO3)(4) (NAB) single crystal laser have been determined from polarized optical absorption and photoluminescence measurements at 7 K. The strongly polarized character of the Nd spectra has been discussed under the assumption of a local D-3 symmetry, higher than the C-2 symmetry of NAB, and the observed energy levels have been labelled with the adequate crystal quantum numbers and irreducible representations. A detailed Hamiltonian of 21 parameters has been used in the simulation of the energy levels and associated wavefunctions of the 4f(3) configuration of Nd3+. The diagonalized complete energy matrix combines simultaneously the free-ion and single-particle crystal field interactions. Starting B-q(k) CF parameters were calculated from the semi-empirical simple overlap model SOM. A comparative simulation considering the C2 symmetry of NAB is provided. Moreover, two-electron CF interactions as well as an empirical correction have been tested in calculating the anomalous splitting of the (2)H2(11/2) levels. A final fit in D-3 symmetry produces a very good adjustment with a low rms deviation sigma = 15.3 cm(-1) between observed and calculated energy levels.