Absorption spectra and energy levels of Gd3+, Nd3+, and Cr3+ in the garnet Gd3Sc2Ga3O12.

Abstract

Absorption spectra measured between 0.3 and 6.7 \ensuremath{\mu}m are reported for ${\mathrm{Gd}}^{3+}$, ${\mathrm{Nd}}^{3+}$, and ${\mathrm{Cr}}^{3+}$ in single-crystal gadolinium scandium gallium garnet, ${\mathrm{Gd}}_{3}$${\mathrm{Sc}}_{2}$${\mathrm{Ga}}_{3}$${\mathrm{O}}_{12}$, at various temperatures. Energy levels split by the crystal field are identified between 1500 and 35 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ${\mathrm{Gd}}^{3+}$(4${f}^{7}$), ${\mathrm{Nd}}^{3+}$(4${f}^{3}$), and ${\mathrm{Cr}}^{3+}$(3${d}^{3}$). The rare-earth ions occupy sites of ${D}_{2}$ point-group symmetry, and chromium ions are found primarily in sites of ${C}_{3i}$ point-group symmetry. A Hamiltonian consisting of Coulombic, spin-orbit, and crystal-field terms is diagonalized to obtain theoretical energy levels for each symmetry. Empirical crystal-field parameters ${B}_{\mathrm{km}}$ were determined by fitting calculated energy levels to observed levels through a variation of the ${B}_{\mathrm{km}}$; these were compared with a lattice-sum calculation. The rms deviations between calculated and observed levels are 1.7 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ${\mathrm{Nd}}^{3+}$ (45 levels), 4.0 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ${\mathrm{Gd}}^{3+}$ (14 levels), and 87.7 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ${\mathrm{Cr}}^{3+}$ (35 levels).