Optical spectroscopy ofYb2Ti2O7andY2Ti2O7:Yb3+and crystal-field parameters in rare-earth titanate pyrochlores

Optical absorption spectra of the ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ single crystals and luminescence spectra of the ${\mathrm{Y}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}:\mathrm{Yb}$ (1%) polycrystalline samples were registered at temperatures $4.2\char21{}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These spectra and earlier published data on magnetic properties of ${\mathrm{Yb}}^{3+}$ ions and on the temperature dependence of the electric field gradient at Yb nuclei in ${\mathrm{Yb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ were used to analyze the crystal-field parameters in rare-earth titanates with the pyrochlore structure. The self-consistent sets of crystal-field parameters for rare-earth ions in the $16d$ sites with the ${D}_{3d}$ symmetry that describe satisfactory all known single-ion magnetic properties and low-energy excitations in ${R}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ crystals ($R=\mathrm{Tb}$, Ho, Er, Tm, Yb) are presented.