Efficient resonant energy transfer occurs within the R-1 line of the (4)A(2) --> E-2 transition of the [Cf(ox)(3)](3-) chromophore in mixed crystal [Rh(bpy)(3)][NaAl1-xCrx(ox)(3)]ClO4 (x = 0.05-0.9, ox = oxalate, bpy = 2,2'-bipyridine). This manifests itself in the form of multiline patterns in resonant fluorescence line narrowing (FLN) experiments at 1.5 K. The conditions for such a resonant process to occur are that the inhomogeneous line width of the R1 line is larger than the zero-field splitting of the ground state, which, in turn, is larger than the homogeneous line width of the transition. The number of lines and their relative intensities depend critically upon the [Cr(ox)(3)](3-) concentration and the excitation wavelength within the inhomogeneous distribution. The basic model for resonant energy transfer as presented by von Arx et al. (Phys. Rev B 1996, 54, 15800) is extended to include the effects of diluting the chromophores in an inert host lattice and of nonresonant R-2 excitation. In addition, Monte Carlo simulations serve to explain the temporal evolution of the multiline pattern following pulsed excitation.