“…The centered bands at 346, 384, 426, 522, 546, 650, 800, 980, and 1554 nm are attributed to the occurred transitions in Er 3+ ion between the ground state 4 I 15/2 and the excited states 2 K 15/2 , 4 G 11/2 , 4 F 3/2 , 2 H 11/2 , 4 S 3/2 , 4 F 9/2 , 4 I 9/2 , 4 I 11/2 , and 4 I 13/2 respectively 58 – 61 . The observed band at 1512 nm arose as a result of the split 4 I 13/2 level 59 , 60 . In Co doped glass ErCoCu2 as shown in Fig.…”