We report the effects of get composition and crystallization condition on the hydrothermal synthesis of optical-clear large AIPO(4)-5 crystals. By using a gel with excessive A] species and high HF content, large perfect hexagonal-shaped AIPO(4)-5 crystals (size 1.25 min x 0.65 mm) were obtained, at a synthesis temperature of 453 K with a crystallization period of 36 h. The optical quality of the crystals is sensitive to the crystallization temperature and time duration. (c) 2005 Elsevier B.V. All rights reserved.