We have developed a new technique, localized spontaneous nucleation, to grow large KBe(2)(BO(3))F(2) (KBBF) single crystals with high optical quality. By localizing the nucleation process in a small, predetermined area, we are able to limit the number of nuclei, which significantly helps us to grow large single crystals and also improve crystal optical quality. KBBF single crystals up to 3.7 mm in thickness have been grown for the first time from KBF(4) and KF-B(2)O(3) solution systems. The quality and defects of KBBF crystals were also discussed. (C) 2010 Elsevier B.V. All rights reserved.