Studies of light-induced charge transfer in Sn2P2S6 by combined EPR/optical absorption spectroscopy

The light-induced charge transfer in ferroelectric tin hypothiodiphosphate Sn2P2S6 is investigated by means of optical absorption and EPR spectroscopy and their combination. Light-induced metastability at 298 K, known to affect the holographic sensitivity, is observed via optical absorption. EPR measurements support the recent identification of holes as the dominating charge carriers. For excitation energies exceeding the band gap of 2.5 eV at 10 K, EPR reveals that the following processes are likely to occur: a hole is captured at one of two different Sn2+ sites, creating Sn3+. At an energy of 1.5 eV the hole is first transferred to the other Sn2+ and for excitation of 2.0 eV to a further center. Since these defects are intrinsic and therefore not limited in quantity, the light-induced sensitisation is a very effective way to improve the holographic performance. (C) 2001 Elsevier Science B.V. All rights reserved.