Mid-infrared ZnGeP2 single crystal was successfully grown by the vertical Bridgman technique under the condition of spontaneous nucleation. By the X-ray Fluorescence analysis method, the constitution of Zn, Ge and P in as-grown ZnGeP2 single crystal was measured. Its defects were studied with an optical microscope. The laser damage threshold of ZnGeP2 crystals was measured to be 55.67 MW/cm(2) at the wavelength of 1064 nm. The transmission spectra of ZnGeP2 were measured at room temperature. By annealing treatment in vacuum, ZnGeP2 powder and a pressure, its optical absorption in the region 0.7-2.5 mu m was found to decrease. (C) 2010 Elsevier B.V. All rights reserved.