1. Centre for Energy Studies; Indian Institute of Technology Delhi; Hauz Khas New Delhi 110016 India
2. Department of Electronics and Information Technology; Ministry of Communications and Information Technology; 6 CGO Complex, Lodhi Road New Delhi 110003 India
3. Luminescent Materials and Devices Group; National Physical Laboratory, Council of Scientific and Industrial Research; Dr. K. S. Krishnan Road New Delhi 110012 India