The influence of monochromatic optical stimulation with wavelengths from 400 to 1100 nm on the characteristics of CdZnTe quasi-hemispherical detectors was studied. It was found that illumination with infrared (IR) light with wavelengths of 870-900 nm close to the absorption edge of the CdZnTe significantly improves the performance of the detector at room temperature. Improvement can be achieved with low-intensity IR illumination at 1-300 μW depending on the chosen wavelength of illumination. Higher intensity illumination was observed to lead to the degradation of the detector's spectrometric characteristics. IR radiation was noted to influence the detector's sensitivity, changing the equilibrium between free and trapped carriers and improving charge collection. For practical purposes, the use of an IR light-emitting diode (LED) as the IR source is suggested. We tested various LEDs with light wavelengths of 770 to 1020 nm. The degree of improvement was different for different detectors due to the different source materials used in the detectors and their dimensions. For example, the performance of a detector that was 10 mm × 10 mm × 5 mm in size with an initial energy resolution (FWHM) of 14.9 keV at 662 keV was improved with an IR LED illumination of up to 8.6 keV. IR stimulation improved the spectrometric characteristics for a wide range of energies starting at 59.6 keV without decreasing detection efficiency and over the temperature range from - 30°C to + 70°C. We found that the use of IR illumination with a properly chosen wavelength not only improves the performance of detectors at low temperatures but also stabilizes them over time.