[1] Govt VYT PG Auto Coll, Dept Phys, Durg 491001, CG, India
[2] Bhilai Inst Technol, Dept Phys, Raipur, CG, India
[3] Rashtrasant Tukadoji Maharaj Nagpur Univ, Dept Phys, Nagpur 440033, Maharashtra, India
[4] Univ Free State, Dept Phys, ZA-9300 Bloemfontein, South Africa