High resistivity CdZnTe:In (CZT:In) single crystals were annealed under Te atmosphere with various annealing times. They were characterized in terms of near-infrared spectrum (NIR), infrared transmission microscopy (IRM), infrared (IR) transmittance, current-voltage (I-V), and photoluminescence (PL) characteristics, and the Am-241 gamma-ray spectra of the detectors were also measured. The results indicated that the concentration of Zn and the density of Te inclusions decreased slightly as the annealing time increased, whereas the resistivity exhibited an initial increase followed by a decrease. The conduction type was changed from weak n-type conduction in the as-grown crystal to p-type conduction in the crystal that was annealed for 240 h. The IR transmittance exhibited no significant change. In the PL spectra, the obvious reduction of the intensity of the (D-0,X) peak and the increase of the intensity of the D-complex peak in the CZT:In crystal that was annealed for 240 h indicated a degradation of the crystal quality. The energy resolution and the corresponding mu tau value of the detector fabricated with crystals that were annealed for 60 h were improved compared to the detector fabricated with as-grown crystals. However, the characteristic peak of the Am-241 gamma-ray could not be observed in the detectors fabricated with crystals annealed for 120 and 240 h. The optimal annealing conditions are a temperature of 773 K and a duration of 60 h. (C) 2013 Elsevier B.V. All rights reserved.