Photoluminescence study of Er-doped zinc-sodium-antimonite glasses

Bulk samples of Er-doped zinc-sodium-antimonite glasses have been investigated by transmission and photoluminescence (PL) spectroscopy. Two series of compositions, (Sb2O3)90−x(Na2O)10(ZnO)x and (Sb2O3)80−x(Na2O)20(ZnO)x, doped with 0.25 mol% Er2O3, have been chosen for this study. Transmission spectra exhibit sharp absorption bands centred at 450, 489, 521, 545, 652, 795, 975 and 1530 nm, which correspond to absorption of Er3+ ions and they are attributed to the optical transitions from the ground state 4I15/2 to the excited states 4F5/2, 4F7/2, 2H11/2, 4S3/2, 4F9/2, 4I9/2, 4I11/2 and 4I13/2, respectively. The optical gap has been found to vary from 3.09 to 3.15 eV with a tendency to decrease at higher Na2O and/or ZnO contents. Four extrinsic bands due to OH−, Si-O, CO2, and (CO3)2− carbonate group vibrations have been identified in the infrared region. Emission spectra are overwhelmed by narrow 4f-4f emission bands. Fine structure of emission bands at 980 and 1530 nm, corresponding to radiative transitions from two lowest excited states of Er3+ ions to the ground state manifold have been investigated at room temperature and at 4 K. A schematic energy diagram of Stark levels splitting for the three lowest manifolds 4I11/2, 4I13/2 and 4I15/2 has been deduced and the nature of temperature broadening of 4f-4f PL bands has been discussed.