Lattice Site of Rare-Earth Ions in Stoichiometric Lithium Niobate Probed by OH− Vibrational Spectroscopy

Kovács, László and Kocsor, Laura and Szaller, Zsuzsanna and Hajdara, Ivett and Dravecz, Gabriella and Lengyel, Krisztián and Gábor, Corradi (2017) Lattice Site of Rare-Earth Ions in Stoichiometric Lithium Niobate Probed by OH− Vibrational Spectroscopy. Crystals, 7 (8). p. 230. ISSN 2073-4352

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Abstract

Rare-earth (RE = Er3+, Nd3+, or Yb3+) ion-doped stoichiometric LiNbO3 crystals were grown by the Czochralski and the high-temperature top-seeded solution growth methods. For the 0.22–0.87 mol% concentration range of the RE oxides in the melt/solution, in addition to the well-known hydroxyl (OH−) vibrational band in undoped stoichiometric LiNbO3, a new infrared absorption band was observed at about 3500 cm−1, similar to the case of the trivalent optical damage resistant (ODR) dopants In3+ and Sc3+. By comparing the frequencies and polarization dependences of the bands to those detected for ODR ion containing crystals, they are attributed to the stretching vibration of OH− ions in RE3+Nb-OH− complexes. Consequently, above a given concentration threshold, some of the rare-earth ions are assumed to occupy niobium sites in the LiNbO3 lattice. The same model is also suggested for RE-doped congruent LiNbO3 crystals containing over-threshold (>5 mol %) amounts of the Mg-co-dopant.

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