Evolution characteristic of OH absorption in Mg (5Â mol% in melt):LiNbO3 crystal with post-grown Li-poor vapor transport equilibration

► Evolution of OH absorption in Mg:LN with Li-poor VTE duration is clearly followed. ► VTE induces a new center resulting in absorption at 3483 cm− 1. ► The VTE duration for crystal fully below photorefractive threshold is ~ 16 h. ► Three-layer model is suggested and supported by experimental results. ► Li out-diffusion theory is established and correlated with three-layer model.