Optical characterization of Cr3+ centers in LiNbO3 |
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Authors: | S.A. Basun A.A. Kaplyanskii A.B. Kutsenko V. Dierolf T. Troester S.E. Kapphan K. Polgar |
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Affiliation: | A.F. Ioffe Physical-Technical Institute, Polytekhnicheskaya 26, 194021 St.-Petersburg, Russia, RU Fachbereich Physik, Universit?t-GH Paderborn, 33095, Germany, DE Fachbereich Physik, Universit?t Osnabrück, 49069, Germany, DE Research Institute for Solid State Physics and Optics, 1121 Budapest, Hungary, HU
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Abstract: | Low-temperature luminescence spectra of stoichiometric Cr:LiNbO3, congruent Cr:LiNbO3 and congruent Cr,Mg:LiNbO3 were studied. Dominant low-field and minor high-crystal-field optical centers are the Cr3+ impurity ions that preferentially occupy Li+ sites (CrLi) in the Cr:LiNbO3 crystals. Low-field centers related to Cr3+ substitution of Nb5+ (CrNb) occur in addition to CrLi in co-doped Cr,Mg:LiNbO3 samples. Application of high hydrostatic pressure leads to the transformation of dominant Cr3+ centers from low- to high-field type due to strong pressure-induced blue shift of the 4 T 2 state, resulting in its crossing with the 2 E state of Cr3+. This level-crossing effect was observed for the dominant Cr3+ Li and Cr3+ Nb centers at pressures that correlate well with estimations based on the 4 T 2-2 Eenergy gap (230 cm-1 and 1160 cm-1) and on the rate of their pressure-induced change (14.35 and 11.4 cm-1/kbar, respectively). We also studied inhomogeneous broadeningof the 2 E?4 A 2transitions at ambient pressure for the minor high-field “defect” Cr3+ Li centers in congruent LiNbO3. A fine structure in the spectral response of these centers was observed. The obtained results are discussed on the basis of a microscopic hierarchic model for perturbed Cr3+ ions in the LiNbO3 lattice. Received: 25 June 2001 / Published online: 2 November 2001 |
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Keywords: | PACS: 81.40.Vw 71.70.Ch 77.84.Dy |
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