Resonant fluorescence line narrowing of the R(1) line of the [Cr(ox)(3
)](3-) chromophore in [Rh(bpy)(3)][NaCr(ox)(3)]ClO4 at 1.6 K neither g
ives rise to the usual three-line pattern nor to spectral diffusion. I
nstead multi-line spectra with spacings equal to the zero-field splitt
ing of the ground state are observed. This phenomenon is attributed to
efficient non-radiative resonant energy transfer within the R(1) line
.