  Light excitation of a semiconductor, known to dynamically-polarize the
nuclear spins by hyperfine contact interaction with the photoelectrons, also
generates an intrinsic nuclear depolarization mechanism. This novel relaxation
process arises from the modulation of the nuclear quadrupolar Hamiltonian by
photoelectron trapping and recombination at nearby localized states. For nuclei
near shallow donors, the usual diffusion radius is replaced by a smaller,
quadrupolar, radius. If the light excitation conditions correspond to partial
donor occupation by photoelectrons, the nuclear magnetization and the nuclear
field can be decreased by more than one order of magnitude.
