Segregation of impurities that cause low infrared (IR) transmission in horizontal Bridgman (HB) grown cadmium zinc telluride (CdZnTe) has been investigated. This segregation was characterized using IR transmission, glow discharge mass spectrometry (GDMS), and IR microscopy measurements. In the studied HB CdZnTe ingots, impurity segregation causes the formation of a small volume in the last-to-freeze portion of the ingot that has high impurity concentration and low IR transmission. Outside this region the concentration of impurities is low and the material shows high IR transmission. The region is visibly observable on CdZnTe slices and appears as a dark area with a sharp boundary. Free carrier absorption within the region causes a decrease in IR transmission with an increase in wavelength and correlates with the concentration of lithium and sodium impurities. Impurity segregation in HB ingots is described and explains the location of the high impurity region. The location of the visible boundary correlates with the first measurable change in IR transmission as compared to the high IR transmission of the surrounding material and supports the hypothesis that the darkening of the region is due to a reduction of the reflectivity due to free carrier absorption. With a properly controlled cool-down recipe, the impurities segregated in the last-to-freeze section of the ingots can remain localized, thereby improving the purity of the remaining bulk of the material.