Affiliation: | a Department of Physics, Sree Vidyanikethan Engineering College, Tirupati 517 102, India b Department of Physics, Changwon National University, Changwon 641-773, South Korea c Department of Physics, Rayalaseema University, Kurnool 518 002, India d Department of Physics, Sri Krishnadevaraya University, Anantapur 515 003, India |