Are the homogeneous Linewidths of spin resonance (ODMR) and optical transitions related?

This paper examines two problems that are central to the question raised in the title. First, we describe formally the origin of homogeneous broadening of ODMR and optical transitions in the presence and absence of spin-orbital couplings between the lowest triplet and other triplet or singlet states. Second, we deduce expressions that relate the spin-to-orbital widths to the rates of orbital and spin scatterings in the singlet and triplet states. In the absence spin-orbital coupling, it is found that the optical width caused by pure dephasing has a much different origin than the ODMR width. In the presence of spin-orbital coupling, on the other hand, the two widths are related and depend on the phonon-induced scattering cross section of the ground electronic state and the other spin sublevel that is involved in the ODMR transition and is not perturbed by spin-orbital interactions. Throughout the paper the coupling of only one triplet sublevel to the singlet was chosen to sufficiently represent the effect of spin-orbital coupling on ODMR and optical widths. Finally, using these theoretical findings we compare the results with some available data on aromatics (ππ*states) and azines and carbonyls (nπ*states) and also conjecture on possible future experiments.