Electron Spin Resonance study of charge trapping in α-ZnMoO4 single crystal scintillator

The origin and properties of electron and hole traps simultaneously appearing in alpha-ZnMoO4 scintillator after X-ray irradiation at low temperatures (T< 35 K) were studied by Electron Spin Resonance (ESR). ESR spectrum of the electron type trap shows pronounced superhyperfine structure due to the interaction of electron spin with nuclear magnetic moments of Mo-95,Mo-97 and Zn-67 lattice nuclei. Considering the nearly tetragonal symmetry of the center this allows us to identify the electron trap as an electron self-trapped at the (Mo(1)O-4)(2-) complex. Nearly 60% reduction of the spin-orbit coupling at the Mo(1) ion is caused by the overlap of the Mo and ligand oxygen orbitals indicating an essential delocalization of the electron over the complex. Holes created by the X-ray irradiation form the O- type defects. Superhyperfine structure of their ESR spectra shows the contributions from two groups of Mo-95,Mo-97 nuclei and from Mg-25 nucleus as an uncontrolled impurity. It proves that namely the O(3) regular oxygen site is transformed into the O- center after the X-ray irradiation. Spectral parameters of the traps have been analyzed in the framework of the crystal field theory. (C) 2015 Elsevier B.V. All rights reserved.