Hydroxyl ion probing transition metal dopants occupying Nb sites in stoichiometric LiNbO3

Transition metal ion (TM = Fe3 +, Cr3+, Ti4+) doped stoichiometric LiNbO3 crystals have been grown by the high temperature top-seeded solution growth and Czochralski methods. Vibrational bands of hydroxyl ions (O H −) have been observed for dopants above a threshold concentration at wavenumbers of 3502 cm−1 for Fe3+ and Cr3+, and 3486 cm−1 for Ti4+. The absorption bands have been attributed to the stretching vibration of O H − ions in M N b n+ – O H − type complexes, where the dopant M occupies a Nb site. The observed vibrational frequencies of the O H − ions and their polarization dependences agree well with the model established for LiNbO3 doped with optical damage resistant (Mg2+, Zn2+, In3+, Sc3+, Hf4+, Zr4+, Sn4+) and rare-earth ions (Nd3+, Er3+, Yb3+), confirming its general validity.