Affiliation: | 1. Department of Physics, Sri Venkateswara University, Tirupati 517502, India;2. Department of Physics, Chadalawada Ramanamma Engineering College, Renigunta Road, Tirupati 517506, India;3. Ceramic and Glass Engineering Department, CICECO, University of Aveiro, Campus Santiago, 3810-193 AVEIRO, PORTUGAL |