The effect of erbium oxide in physical and structural properties of zinc tellurite glass system by Shahrol, Nazirul Nazrin, Mohamed Kamari, Halimah, Muhammad, Farah Diana, Yip, Jen Sheng, Laoding, Hasnimulyati, Mohd Fudzi, Faznny, M.A., Hazlin, Ismail, Zaitizila