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RESEARCH PAPER

Investigation on the EPR Parameters for Tetragonal VO2+ Centers in LiHSO4 Single Crystals Wu-Tong Chen1 • Bao-Fang Zhang1 • Qin-Yi Zhu1 • Ting-Ting Lu1 Wen-Rui Jia1 • Zhuo Cao1 • Ji-Zi Lin2

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Received: 8 May 2020 / Accepted: 17 July 2020 Ó Shiraz University 2020

Abstract In this work, the electron paramagnetic resonance (EPR) parameters (g-factors and A-constants) of the tetragonal VO2? centers in LiHSO4 single crystals are theoretically investigated by the high-order perturbation formulae for these parameters based on two-spin–orbit-parameter model. Since the spin–orbit coupling coefficient of the ligand O2- is close to that of the central ion V4? for the present system with strong covalence, the contributions to the EPR parameters from the ligand p- and s-orbitals as well as the spin–orbit coupling coefficient of the O2- ligand should be considered. The requirements of the crystal-field parameters are determined from the optical spectrum. The calculated results show good agreement with the experimental values. The signs of A-constants are ascertained in the discussion. Keywords Electron paramagnetic resonance  Crystal field  Two-spin–orbit-parameter model  VO2?  LiHSO4

1 Introduction Transition metal ion and rare-earth ion are often used as the active ions in most new functional materials, such as laser materials, magnetic materials and nonlinear optical materials (Ramteke et al. 2017; Wilson 2019; Almeida et al. 2019; Kaczmarek 2007; Fletcher et al. 2012), which have received much attention due to the great potential application in medicine, optical communication, military and other fields (Ma et al. 2009; Renfrew 2018; Maqbool and Corn 2010; Jung et al. 2017). The vanadyl ion (VO2?) doped in host crystal has aroused extensive interest of researchers, because doping VO2? in the optical crystals can be helpful for not only the studies for the optical properties of such optical materials but also the

& Ji-Zi Lin [email protected] 1

Department of Electronic Information Engineering, Suzhou Institute of Technology, Jiangsu University of Science and Technology, Zhangjiagang 215600, People’s Republic of China

2

Department of Physics, Suzhou Institute of Technology, Jiangsu University of Science and Technology, Zhangjiagang 215600, People’s Republic of China

understanding of the local distortion structure information of these materials (Ding et al. 2018; Srinivas et al. 2019; Reddy et al. 2017; Li et al. 2015a, b; Zhang et al. 2014). For example, the EPR studies for VO2? ions in LiHSO4 single crystals were carried out by Maurya et al. (1995), and the anisotropic g-factors (gk, g\) and the hyperfine structure constants (Ak, A\) were also obtained for this center (Maurya et al. 1995). Based on the EPR and optical absorption studies, the oxygen octahedron around the central ion V4? was assumed to show tetragonal compression distortion (Maurya et al. 1995). However, until now, the EPR results were not satisfactorily interpreted, except that the si