Modulation sidebands spectra within inhomogeneous CW-EPR line detected by double modulation EPR spectroscopy.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Materials Science

Background:

• Conventional modulation spectroscopy (MS) in continuous wave electron paramagnetic resonance (CW-EPR) uses radiofrequency (RF) fields exceeding spectral linewidths.
• Double modulation spectrum (DMS) is introduced as a specialized form of MS applicable to homogeneous lines.

Purpose of the Study:

• To present and analyze double modulation spectra (DMS) as a method for studying electron paramagnetic resonance (EPR).
• To demonstrate the capability of DMS in extracting spin-lattice (T1) and spin-spin (T2) relaxation times from inhomogeneous lines.
• To explore the potential of DMS in improving detection sensitivity for paramagnetic centers with long relaxation times.

Main Methods:

• Numerical simulations of DMS using multi-photon transitions formalism (one microwave photon + multiple RF photons).
• Application of the DMS method to analyze the E' defect in irradiated vitreous SiO2.
• Investigation of the 'rapid passage' effect on DMS sensitivity.

Main Results:

• DMS of inhomogeneous lines exhibit a basic structure similar to MS with sideband peaks at multiples of basic radiofrequencies.
• The linewidths of DMS peaks are significantly narrower (2-3 orders of magnitude) than the inhomogeneous linewidth.
• Extracted T1 and T2 relaxation times from the E' defect in SiO2 correlate with underlying homogeneous linewidth components.
• The 'rapid passage' effect enhances DMS detection sensitivity for paramagnetic centers with long relaxation times.

Conclusions:

• Double modulation spectroscopy (DMS) is a valuable complementary technique for analyzing inhomogeneous broadening in EPR spectra.
• DMS enables the extraction of T1 and T2 relaxation times, providing insights into the dynamics of paramagnetic centers.
• The method shows promise for studying systems with long relaxation times due to improved detection sensitivity.