1. DST/CSIR Nanotechnology
Innovation Centre, National Centre for Nano-Structured Materials, Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001, South Africa
2. CSIR-National Laser Centre, 626 Meiring
Naude Rd., Brummeria, Pretoria 0001, South Africa
3. Department
of Physics, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
4. Department
of Physics, University of the Free State, P.O. Box 339, Bloemfontein ZA9300, South Africa
5. School
of Chemistry and Physics, Westville Campus, University of KwaZulu-Natal, Private
Bag X54001, Durban 4000, South Africa