Photoinduced trapping of charge at sulfur vacancies and copper ions in photorefractive Sn2P2S6 crystals
Abstract
Electron paramagnetic resonance (EPR) is used to monitor photoinduced changes in the charge states of sulfur vacancies and Cu ions in tin hypothiodiphosphate. A Sn2P2S6 crystal containing Cu+ (3d10) ions at Sn2+ sites was grown by the chemical vapor transport method. Doubly ionized sulfur vacancies (VS2+) are also present in the as-grown crystal (where they serve as charge compensators for the Cu+ ions). For temperatures below 70 K, exposure to 532 or 633 nm laser light produces stable Cu2+ (3d9) ions, as electrons move from Cu+ ions to sulfur vacancies. A g matrix and a 63,65Cu hyperfine matrix are obtained from the angular dependence of the Cu2+ EPR spectrum. Paramagnetic singly ionized (VS+) and nonparamagnetic neutral (VS0) charge states of the sulfur vacancies, with one and two trapped electrons, respectively, are formed during the illumination. Above 70 K, the neutral vacancies (VS0) are thermally unstable and convert to VS+ vacancies by releasing an electron to the conduction band. These released electrons move back to Cu2+ ions and restore Cu+ ions. Analysis of isothermal decay curves acquired by monitoring the intensity of the Cu2+ EPR spectrum between 74 and 82 K, after removing the light, gives an activation energy of 194 meV for the release of an electron from a VS0 vacancy. Warming above 120 K destroys the VS+ vacancies and the remaining Cu2+ ions. The photoinduced EPR spectrum from a small concentration of unintentionally present Ni+ ions at Sn2+ sites is observed near 40 K in the Sn2P2S6 crystal.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Feb 23, 2021
- Source ID
- 10.1063/5.0042905
Entities
People
- Alexander A. Grabar
- David Evans
- E. M. Golden
- E. M. Scherrer
- Jonathan E. Slagle
- L E Halliburton
- N. C. Giles
- S. A. Basun
- T. D. Gustafson
Organizations
- Air Force Institute of Technology
- Air Force Office of Scientific Research
- Air Force Research Laboratory
- Azimuth Corporation
- Science and Technology Center in Ukraine
- Uzhhorod National University
- West Virginia University