A method is provided including acquiring detection events with a radiation detector that includes a semiconductor plate. Electrons and holes are generated in the semiconductor plate responsive to absorption of ionizing radiation. The holes including groups of holes having different effective masses for corresponding different valence energy bands. The method also includes optically coupling infrared (IR) radiation into the semiconductor plate of the radiation detector. The IR radiation has at least one wavelength selected from a spectral range including wavelengths to which the semiconductor plate is partially transparent. The wavelengths of the IR radiation are configured to excite at least some of the holes from a first group at a first valence energy band to a second group at a second valence energy band, with the holes of the second group having lower effective masses than corresponding holes of the first group.