Antiresonance in the Optical Spectrum ofEu3+inEu3Ga5O12:Pt

Abstract

The absorption line shape of the ${\mathrm{Eu}}_{3+}$ $^{7}F_{0}\ensuremath{-}\mathrm{to}\ensuremath{-}^{5}D_{0}$ transition is severely modified in garnet crystals where there is an overlapping absorption band from an impurity such as Pt. Below 77 \ifmmode^\circ\else\textdegree\fi{}K the transition has a dispersionlike line shape which changes as the temperature is increased to an approximate antiresonance at 300 \ifmmode^\circ\else\textdegree\fi{}K. The absorption was fitted to Fano's line-shape formula and the four parameters were obtained as a function of temperature. Weak antiresonances are also observed near the $^{7}F_{0}$ to $^{5}D_{1}$ transitions. A two-ion model consisting of one ion with sharp-line states and a second with a broad absorption band is shown to reproduce Fano's line-shape formula. The interion coupling results from a transfer of excitation between the sharp line and the band and the coupling is shown to be consistent with an anisotropic superexchange interaction.