Modulation frequency dependence of continuous-wave optically/electrically detected magnetic resonance

Continuous-wave optically and electrically detected magnetic resonance spectroscopy (cwODMR/cwEDMR) allow the investigation of paramagnetic states involved in spin-dependent transitions, like recombination and transport. Although experimentally similar to conventional electron spin resonance (ESR), there exist limitations when applying models originally developed for ESR to observables (luminescence and electric current) of cwODMR and cwEDMR. Here we present closed-form solutions for the modulation frequency dependence of cwODMR and cwEDMR based on an intermediate pair recombination model and discuss ambiguities which arise when attempting to distinguish the dominant spin-dependent processes underlying experimental data. These include (1) a large number of quantitatively different models cannot be differentiated; (2) signs of signals are determined not only by recombination but also by other processes like dissociation, intersystem-crossing, pair generation, and even experimental parameters, such as modulation frequency, microwave power, and temperature; (3) radiative and nonradiative recombination cannot be distinguished due to the observed signs of cwODMR and cwEDMR experiments.