Site-selective polarized spectroscopy of trivalent holmium-doped yttrium aluminum garnet

Site-selective, polarized measurements of laser-induced fluorescence of ${\mathrm{Ho}}^{3+}$ ions in a specially oriented sample of yttrium aluminum garnet (YAG) are reported. To overcome the optical isotropy of the cubic YAG host, a sample was cut from a ${\mathrm{Ho}}^{3+}$:YAG boule in a manner that favored the excitation and detection of fluorescence from ${\mathrm{Ho}}^{3+}$ ions residing in specifically oriented sites in the YAG crystal lattice. Careful selection of crystal orientation, excitation and detection wavelengths, excitation-detection geometry, and polarization of incident and emitted radiation permitted analysis of ${\mathrm{Ho}}^{3+}$ ions on those sites. This approach facilitated the identification of the electric or magnetic dipole character of 25 selected excitation and emission transitions, and also provided data that support previous assignments of symmetry labels of the Stark levels involved in those transitions.