Cryst. Res. Technol. 42, No. 7, 718 – 722 (2007) / DOI 10.1002/crat.200610894 © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Influence of doping on OH absorption in LiNbO 3 crystals R. K. Choubey 1 , B. Q. Khattak 2 , S. Kar 3 , P. Ramshankar 2 , P. Sen 1 , and K. S. Bartwal* 3,4 1 Department of Applied Physics, SGSITS, Indore - 452 003, India 2 Chemical Treatment Facility 3 Laser Materials Development & Devices Division, Raja Ramanna Centre for Advanced Technology, Indore – 452 013, India 4 Advanced Materials Division, Korea Research Institute of Chemical Technology, KRICT P.O. Box 107, Yusong-Gu, Daejeon, South Korea Received 27 February 2007, accepted 23 March 2007 Published online 10 June 2007 Key words optical materials, crystal growth, IR spectroscopy, optical properties. PACS 81.10.Fq, 81.10.h Undoped, Cr doped and Mg, Cr codoped LiNbO 3 crystals were grown by conventional Czochralski technique. Comparative study was carried out using Fourier transform infrared (FTIR) and UV-Visible spectroscopy. Infrared optical absorption for OH ion has been used to study the effect of dopants on the crystals. The peak position of OH shift to 3535 cm -1 for Mg, Cr codoped crystals compared to 3484 cm -1 for undoped and Cr doped crystals. Prominent absorption bands are found in the visible region centered at 480 nm (20833 cm -1 ) and 653 nm (15313 cm -1 ) in Cr doped crystals. Whereas in Mg, Cr codoped crystals these broad absorption bands are red shifted to 517 nm (19342 cm -1 ) and 678 nm (14749 cm -1 ). UV cutoff in Cr doped crystals shift towards higher wavelength compared to undoped LiNbO 3 crystals. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Lithium niobate, LiNbO 3 (LN) is a ferroelectric crystal with variety of applications. The OH  ions, which are always present in air grown LiNbO 3 , are assumed to affect the photorefractive behavior [1]. The lattice positions for optically active impurities (transition metals and rare earth ions) in LN crystals have been extensively studied. The location of Cr 3+ ions in LN has been investigated by optical, electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) techniques [2]. Optical spectroscopy of the Cr 3+ ions in LiNbO 3 crystals and codoped with MgO has been studied by Jaque et al. [3]. Recently, we have reported the effect of codoping on crystalline perfection of Mg:Cr:LiNbO 3 crystals using high resolution X-ray diffraction (HRXRD) technique [4, 5]. The well-established band structure approach for variation in optical properties of LiNbO 3 crystal is given by Kityk et al. [6, 7]. It is known that in Czochralski grown LN crystals the moisture enters during the growth processes. In LiNbO 3 crystal, the position of OH  absorption bands are affected by Mg, Fe, Cr, Sc and rare earth ions [8]. Changes in the OH  polarization absorption in LiNbO 3 lattice perturbed by addition of other impurities have been reported in the literature [9]. The characterization of OH  centers formed in LiNbO 3 crystals are important to explain many features for optical applications. The OH  absorption spectra of highly doped LiNbO 3 , such as MgO, ZnO, In 2 O 3 , and Sc 2 O 3 , have also been widely investigated. Band shifts from 3484 cm -1 to about 3535 cm -1 for divalent ions and to 3504 cm -1 for trivalent ions were observed when the doping concentration is above a certain threshold value. The thresholds for divalent and trivalent ions were reported as 5.5 and 2.5 mol%, respectively [10]. The 3504 cm -1 peaks were also found for some trivalent ions (such as In 3+ , ____________________ * Corresponding author: e-mail: bartwalks@yahoo.co.in