1. School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai, P. R. China
2. Department of Physics, National Institute of Technology, Calicut, Calicut, Kerala, India
3. Department of Physics, VTMNSS College, Dhanuvachapuram, Thiruvananthapuram, Kerala, India
4. Department of Physics and Atmospheric Sciences Program, Michigan Technological University, Houghton, Michigan, USA