Energy-level and line-strength analysis of optical transitions between Stark levels in Nd3+:Y3Al5O12.

Abstract

Results obtained from optical absorption measurements on ${\mathrm{Nd}}^{3+}$:${\mathrm{Y}}_{3}$${\mathrm{Al}}_{5}$${\mathrm{O}}_{12}$ (Nd:YAG) at 10 and 29 K are reported and analyzed. The low-temperature (10 K) absorption spectrum shows transitions from the lowest Stark component of the $^{4}$${\mathit{I}}_{9/2}$ (ground) multiplet to 133 of the 155 crystal-field (Stark) levels predicted to be located between 3900 and 40 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, spanning 35 excited multiplet manifolds of ${\mathrm{Nd}}^{3+}$(4${\mathit{f}}^{3}$). Among the 133 transitions observed in the 10-K absorption spectrum, 97 are sufficiently well resolved to permit quantitative determination of transition line strengths. Energy levels for the $^{4}$${\mathit{I}}_{9/2}$ and $^{4}$${\mathit{I}}_{11/2}$ multiplets are taken from previously obtained optical emission measurements, and the resulting 144-level data set is analyzed in terms of a model Hamiltonian that assumes ${\mathrm{D}}_{2}$ site symmetry for the ${\mathrm{Nd}}^{3+}$ ions in Nd:YAG. Inclusion of two-electron correlation crystal-field (CCF) interaction terms in the model Hamiltonian explains the crystal-field splittings of several anomalous multiplets, and reduces the rms deviation between calculated and observed energies (for 144 levels) from 28 to 14 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The optical line-strength data obtained in this study are analyzed in terms of an f-f transition intensity model developed by us in previous work. This model has broad applicability in analyses of f-f intensity data for transitions between Stark levels. Emission branching ratios for transitions from the $^{4}$${\mathit{F}}_{3/2}$ multiplet are calculated and compared with literature values.