Optically-pumped NMR

This review will include both types of studies, but will not discuss in any detail optically pumped NMR of semiconductors, which has been well-reviewed [5, 11, 12,14], or other unconventional techniques for detection of NMR signals. Physics-related NMR studies of more complicated semiconductor behavior such as Kondo insulators or semiconductors and other unusual semiconducting phases, and semiconducting phases of high-Tc superconductors, while very important in physics, will be neglected here. I have deemed it of some value to provide rather extensive citation of the older as well as of the more recent literature, since many of the key concepts and approaches relevant to current studies (e.g., of nanoparticle semiconductors) can be found in the older, often lesser-known, literature. My overall aim is to provide a necessarily individual perspective on experimental and theoretical approaches to the study of semiconductors by NMR techniques that will prove useful to chemists and other scientists. 

R 605 A. Goto, T. Shimizu and K. Hashi, Excitation Spectra in Compound Semiconductors Observed by the Optical Pumping NMR Method , Kotai Butsuri, 2004,39,497... 

Fig. 5.3.8 Photograph of the detection region of the NMR probe with radiofrequency coil. A methane—air mixture was ignited above the zeolite pellets. The mixture also contained xenon for NMR detection. Hp-129Xe NMR spectra with 30% xenon (from high-density xenon optical pumping) in 70% methane is depicted. (1) The spectrum in the absence of combustion and (2) the spectrum during combustion. Adapted from Ref. [2],...

Answer. There has been little effective interplay between experimental results obtained on single nanostructures grown as quantum-wells and studied by optical-pumping methods and those obtained on bulk nanoscale semiconductors by more conventional NMR approaches. However, this situation may change, since the former studies can provide information about the effects of, e.g., charge carriers or strain or compositional interfaces upon NMR parameters such as chemical and Knight shifts and EFGs in reasonably well-defined systems. 

Applications of Optical Pumping and Polarization Techniques in NMR I. Optical Nuclear Polarization in Molecular Crystals... 

The combination of collinear fast-beam laser spectroscopy and P-RADOP (radiation-detected optical pumping) has been used to measure nuclear spins and moments of neutron-rich isotopes of the light alkali elements jLi [72-74] and Na [75]. Here, the optically pumped fast atomic beam is implanted into a single crystal placed in a static magnetic field. The NMR signal is destroying the nuclear polarization detected by measuring the p-decay asymmetry. 

A well-known and important phenomenon in the area of nuclear-spin resonance (NMR) in gases, liquids, or solid samples is dynamic nuclear-spin polarisation (DNP) (see e.g. [M6]). This term refers to deviations of the nuclear magnetisation from its thermal-equilibrium value, thus a deviation from the Boltzmann distribution of the populations of the nuclear Zeeman terms, which is produced by optical pumping (Kastler [31]), by the Overhauser effect [32], or by the effet solide or solid-state effect [33]. In all these cases, the primary effect is a disturbance of the Boltzmann distribution in the electronic-spin system. In the Overhauser effect and the effet solide, this disturbance is caused for example by saturation of an ESR transition. Owing to the hyperfine coupling, a nuclear polarisation then results from coupled nuclear-electronic spin relaxation processes, whereby the polarisation of the electronic spins is transferred to the nuclear spins. 

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