Abstract
The optical spectra and the second-harmonic generation (SHG) are studied in a noncentrosymmetric GdFe3(BO3)(4) magnet. In the region of weak absorption (alpha similar to 20-400 cm(-1)) below similar to3 eV, three absorption bands are distinguished, which can be unambiguously assigned to forbidden electronic transitions from the ground (6)A(1) state of the Fe3+ ion to its excited states T-4(1) (similar to1.4 eV), T-4(2) (similar to2 eV), and (4)A(1), E-4 (similar to2.8 eV). Intense absorption begins in the region above 3 eV (alpha similar to 2-4 x 10(5) cm(-1)), where two bands at similar to4.0 and 4.8 eV are observed, which are caused by allowed electric dipole charge-transfer transitions. The spectral features of SHG in the 1.2-3.0-eV region are explained by a change in the SHG efficiency caused by a change in the phase mismatch. It is shown that in the weak absorption region, phase matching can be achieved for SHG. (C) 2004 MAIK "Nauka / Interperiodica".
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