Fluorescence line narrowing Zeeman spectroscopy of Cr3+-doped Gd3Sc2Al3O12 garnet crystals. II. Calculation of the lineshape

Abstract

For pt.I see ibid., vol.4, p.7307 (1992). The R1 line of Cr3+ in an antiferromagnetic garnet crystal Gd3Sc2Al3O12 (GSAG) is broadened inhomogeneously and homogeneously. Site-selective techniques, such as fluorescence line narrowing (FLN), can remove the inhomogeneous broadening created by strain and compositional disorder. The FLN spectrum then reflects the broadening due to processes including spin-spin exchange interaction between Cr3+ ions in octahedral positions and Gd3+ ions in dodecahedral positions in the GSAG unit cell. A magnetic field can remove the homogeneous broadening due to antiferromagnetic exchange. The R1 line is associated with the spin-forbidden 2E to 4A2 transition. In general, the selection rule on the R1 line breaks down through spin-orbit interaction on the Cr3+ ion. Simulations of the FLN spectra of Cr3+:GSAG as a function of both temperature and magnetic field have been used to estimate the magnitude of the spin-spin exchange coupling constant, J approximately=0.25-0.33 cm-1. Such simulations also show that for the 2E to 4A2 transition to antiferromagnetic GSAG the Gd3+ spin in the Cr3+-Gd3+ spin exchange system is conserved in the presence of a magnetic field (B>2T), whereas the selection rule breaks down in the absence of a magnetic field.