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Optical enhancement of NMR signals in CdTe Leung, Isaac J. H.


Optical pumping is a powerful tool for increasing the sensitivity of NMR experiments. While it has been widely studied in GaAs, InP and other semiconductors, no previous observations have been made using direct RF inductive NMR techniques on CdTe. We have observed optically enhanced NMR signals from ¹²³Te, ¹²⁵Te, ¹¹¹Cd and ¹¹³Cd in a single crystal of CdTe under excitation with near band-gap illumination. Unlike GaAs or InP, CdTe is unique in that the NMR observable isotopes naturally exist in very low abundances. This provided an opportunity to test the validity of two models describing the mechanism of optical enhancement. From a comparison of the amplitudes of the NMR signals observed from the different nuclear species, we conclude that the optical enhancement of the nuclear spin polarization in the bulk semiconductor is not consistent with a mechanism that relies on spin diffusion, but may be consistent with a recently proposed mechanism involving the direct polarization of the bulk from optically excited excitons. Optically enhanced NMR signals are observed at temperatures as high as 100 K using a tuneable 1 W laser.

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