Laser-induced polarized fluorescence in cubic yttrium sesquioxide doped with trivalent europium

The fluorescence spectrum of ${\mathrm{Eu}}^{3+}$ in the $C_2$—approximately $C_{2v}$—site of the $C$-${\mathrm{Y}}_2$ ${\mathrm{O}}_3$ structure was recorded using a tunable dye laser to populate the ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}$ level of the $4f^6$ configuration. Because the active ion occupies an anisotropic point site in an overall cubic unit cell one can make use of the Feofilov theory to interpret the experimental polarization of the emission lines. The polarized laser beam was applied perpendicular to the (111) plane of a single crystal and the polarization for each line of the ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}\to {}_{}{}^7{}_{}{}^{}F_{1,2,3,4}^{}{}_{}{}^{}$ transitions was measured. From the data the irreducible representations associated with the Stark levels can be found. In particular the transitions $A_1\to A_1$ and $A_1\to A_2$ can be unambiguously distinguished from $A_1\to B_1$ and $A_1\to B_2$. A preliminary crystal-field analysis was undertaken on the basis of the 49 ${}_{}{}^7{}_{}{}^{}F_J^{}{}_{}{}^{}$ states using an Hamiltonian (including spin-orbit coupling) written in true $C_2$ symmetry, that is including imaginary crystal-field parameters. To derive approximate values of the crystal-field parameters the electrostatic point-charge model was applied.