1. Chemistry and Physics of Materials Unit; Jawaharlal Nehru Centre for Advanced Scientific Research; Bangalore 560064 India
2. Optoelectronics Group; Cavendish Laboratory; University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE; U.K
3. International Centre for Materials Science; Jawaharlal Nehru Centre for Advanced Scientific Research; Bangalore 560064 India
4. School of Advanced Materials; Jawaharlal Nehru Centre for Advanced Scientific Research; Bangalore 560064 India