Photoinduced absorption spectra of ZnS:Fe crystals

Photoinduced absorption (PA) spectra of ZnS:Fe crystals are measured between 0.3 and 3.6 eV by means of a modulation technique. Transitions related to the charge states Fe 3+ and Fe + , which have been detected by EPR a long time ago, are believed to be seen in these spectra. In particular, the processes Fe 3+ → Fe 2+ + h and Fe 2+ + Fe 3+ + e are identified, the latter manifesting itself most clearly in the excitation spectrum of the PA band due to the former transition. The shapes of the photoneutralization and photoionization spectra are discussed, and the position of the Fe + ground state in the forbidden gap is estimated.