1. Centre for Nanoscience and Nanotechnology, Sathyabama University, Chennai 600 119, India
2. Department of Physics, Maamallan Institute of Technology, Sriperumpudur 602 105, India
3. Directorate of Distance Education, Alagappa University, Karaikudi 630 003, India
4. Crystal Research Lab, Department of Physics, Anna University, Chennai 600 025, India