MAGNON-ASSISTED CHROMIUM EMISSION IN YCRO3 LUCRO3 AND GDCRO3

Measurements have been made of the absorption and fluorescence spectrum of Cr3+ in orthorhombic YCrO3, LuCrO3, and GdCrO3. We observe several very sharp emission lines at energies about 100 cm-1 lower than the intrinsic 4A2 to 2E Cr3+ absorption, and attribute the emission to impurity-perturbed Cr3+ ions. Intrinsic emission was not observed. Magnon sideband fluorescence is found at lower energy and results in the simultaneous optical de-excitation of a perturbed Cr3+ ion and the creation of a magnon on a neighboring lattice site. The sideband is spin allowed if the photon and magnon are created on the same sublattice, and has electric dipole polarization. Analysis of the sideband line shape shows the nearest-neighbor exchange interaction between pairs along the c axis, and between pairs in the plane perpendicular to the c axis are not equal. The value of J averaged over the six nearest neighbors is 22.1, 17.6, and 25.5 cm -1 for the Y, Lu, and Gd chromites, respectively. These results are in good agreement with J values computed from magnetic data. © 1969 The American Institute of Physics.