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

• Published in: Crystals (Basel) 2017-08, Vol.7 (8), p.230
• Main Authors: Kovács, László, Kocsor, Laura, Szaller, Zsuzsanna, Hajdara, Ivett, Dravecz, Gabriella, Lengyel, Krisztián, Corradi, Gábor
• Format: Article
• Language: English
• Subjects: Absorption spectra; Dopants; hydroxyl ions; Infrared absorption; IR spectroscopy; lithium niobate; Lithium niobates; Niobium; Rare earth elements; rare-earth dopants; Stretching
• ISSN: 2073-4352; 2073-4352
• DOI: 10.3390/cryst7080230

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.