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

• The charge traps created by X-ray irradiation in the α-ZnMoO4 were studied by ESR.
• An electron trap was an electron self-trapped at the (Mo(1)O4)3− complex.
• We show delocalization of the self-trapped electron over the complex.
• A hole trap was a hole trapped and stabilized at the O(3) regular oxygen site.
• We report a complete set of the corresponding spin Hamiltonian parameters.

The origin and properties of electron and hole traps simultaneously appearing in α-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 95,97Mo and 67Zn 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)O4)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 95,97Mo nuclei and from 25Mg 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.