Techniques, Theory, and Biological Applications of Optically Detected Magnetic Resonance (ODMR)

Abstract

The past dozen years or so have witnessed the application of a new spectroscopic method to the investigation of biological molecules. Optical detection of triplet-state magnetic resonance (ODMR) represents in the broadest sense a combination of optical measurement (phosphorescence, fluorescence, absorption) with electron spin resonance (ESR) spectroscopy. In ODMR, microwave-induced transitions between magnetic sublevels of the lowest triplet state are detected by their effect on some optical property of the sample which is monitored simultaneously. Historically, the field may be traced back to early work on optical detection of magnetic resonance transitions of atoms and ions in the gas phase by Fermi and Rasetti (1925), Breit and Ellet (1925), and by Brossel and Bitter (1952). The first optically detected magnetic resonance experiment in the solid state was reported by Geschwind et al. (1959) on the 2E excited state of Cr3+ in ruby at 1.6 K. This early work has been reviewed by Bernheim (1965). At about the time of Geschwind’s experiment, Hutchinson and Mangum (1958; 1961) made the first ESR measurements on a photoexcited triplet state in the solid state—the phosphorescent (T 1) state of naphthalene substitutionally incorporated in a single crystal of durene.