Composition determination of off-congruent Li-deficient MgO (5 mol%)-doped LiNbO₃ crystals by absorption spectroscopy

¹ Department of Opto-Electronics and Information Engineering, School of Precision Instruments and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, P.R. China
² Key Laboratory of Opto-Electronics Information Technology, Tianjin University, Ministry of Education, Tianjin 300072, P.R. China
³ Department of Electronic Engineering, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, P.R. China

^a e-mail: dlzhang@tju.edu.cn

Received: 29 April 2011
Revised: 23 September 2011
Accepted: 14 October 2011
Published online: 2 December 2011

Abstract

Off-congruent Li-deficient MgO:LiNbO₃ crystals were prepared by carrying out post-grown Li-poor vapor transport equilibration (VTE) treatments on a number of 0.47 mm thick MgO (5 mol% in growth melt or 6 mol% in crystal)-doped, initially congruent LiNbO₃ plates at 1100 °C over different durations ranged in 40–395 h. At first, the VTE-induced Li composition reduction was measured as a function of the VTE duration using the gravimetric method. Then, optical absorption spectroscopy was applied to study the crystal composition effects on the fundamental optical absorption edge and OH absorption characteristic parameters including the peaking position, band width, peaking absorption and band area. These crystal composition effects enable one to establish the optical methods used for determination of the crystal composition from the spectroscopic measurements. These optical methods overcome the demerit that the gravimetric method is limited to a specific VTE temperature or crystal thickness, and can be applied to design and produce an MgO-doped crystal with desired Li composition.