Optical properties of manganese-doped yttrium orthoaluminate crystals (Mn:YAlO 3 ), grown by the Czochralski technique, are reported. Luminescence and absorption spectra indicate the presence of Mn 4ϩ ions in as-grown crystals, and Mn 3ϩ , Mn 4ϩ , and Mn 5ϩ ions simultaneously in photoexcited crystals. A permanent diffraction grating, erasable by heating, was obtained in the crystals with diffraction efficiency of more than 50% at 514.5 nm reading wavelength and 1-2 % in 632-930 nm wavelength range. Reading at wavelengths longer than 630 nm did not damage the recorded grating. The electro-optical effect observed in the photoexcited crystals implies that manganese ions disturb the YAlO 3 crystal structure so that it becomes noncentrosymmetric.
A sharp microwave response centered at zero magnetic field was observed in manganese- and iron-doped Na2O–CaO–MgO–SiO2 glasses with phase opposite to the normal Mn+2 and Fe+3 paramagnetic signals. The response can be described as magneto-induced microwave conductivity in the dielectric glass that derives from spin-dependent charge migration within the first coordination sphere of the paramagnetic ion. In contrast to the spin-polarized tunneling in ferromagnets between different valence states of metals, the observed effect is due to spin-dependent tunneling that occurs in the vicinity of manganese or iron in diluted paramagnetic systems.
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