NMR study of holographic Mu-doped yttrium orthoaluminates

The quadrupole coupling constants, asymmetry parameters and spin-lattice re laxation time of Al-27 nuclei have been studied in Mn-doped YAlO3 crystals. The dependence of the relaxation time on temperature and concentration of Mn ions implies a mechanism of relaxation via Mn2+ paramagnetic ions taking into account the nuclear spin diffusion partly restricted by the diffusion barrier. A substantial increase of the relaxation times was observed in th e photoexposed samples. We ascribe this effect to the appearance of fast-re laxing Mn5+ ions produced by photoionization of Mn4+ centers.