Electron paramagnetic resonance spectroscopy (EPR)

Electron paramagnetic resonance (EPR) or electron spin resonance spectroscopy is an experimental technique that allows obtaining information on the quantity, the chemical composition, and the microscopic structure of the paramagnetic centers under study. The presence of atoms with nonzero nuclear magnetic moment can be detected by the presence of hyperfine signals, for obtaining additional information on the environment of a given center. The chapter presents the EPR lineshape of paramagnetic systems consisting of powdered crystal or embedded in amorphous materials. In many systems, the unpaired electron can be located near one or more atoms having nonzero nuclear spin. The resonant cavity efficiency in accumulating microwave energy is given by its quality factor; it depends on different factors and affects the sensitivity of the EPR spectrometer. The signal-to-noise ratio is increased using a RC filter and finally an analogical digital integrator, with selectable integration time, integrates the signal and the latter is displayed on the screen of the EPR spectrometer computer.