1. Department of Physics Kazi Nazrul University Asansol 713340 WB India
2. Centre for Organic Spintronics and Optoelectronics Devices Kazi Nazrul University Asansol 713340 WB India
3. Solid State Physics Division Bhabha Atomic Research Centre Mumbai 400085 India
4. Homi Bhabha National Institute Anushaktinagar Mumbai 400094 India