1. International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University 1 , Kottayam, Kerala 686 560, India
2. Univ. Rennes, INSA Rennes, CNRS, Institut FOTON – UMR 6082 2 , F-35000 Rennes, France
3. School of Nanoscience and Nanotechnology, Mahatma Gandhi University 3 , Kottayam, Kerala 686 560, India
4. School of Pure and Applied Physics, Mahatma Gandhi University 4 , Kottayam, Kerala 686 560, India