ZnGeP2 crystal is the leader among nonlinear crystals for middle IR. Large sized Phi 20 x 90 mm(3) ZGP single crystals have been grown successfully by the vertical gradient freeze technique. The crystallinity and optical properties of as-grown crystals were measured by XRD and transmission spectra respectively. The thermal conductivity was tested using PPMS. The absorption coefficient can be reduced to 0.08 cm(-1) at 2 mu m by post-annealing. The fabricated devices were also utilized to demonstrate SHG and OPO experiments for nonlinear optical applications. (C) 2012 Elsevier B.V. All rights reserved.