Upconversion studies in Er3+ doped TeO2-M2O (M = Li, Na and K) binary glasses

摘要

The luminescence properties of Er3+ doped alkali tellurite [TeO2-M2O (M = Li, Na and K)] glasses are investigated. Infrared to visible upconversion emissions are observed at 410, 525, 550 and 658 nm using 797 nm excitation. These bands are assigned to the H-2(9/2) -> I-4(15/2), H-2(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2), F-4(9/2) -> I-4(15/2) transitions of Er3+ respectively. Detailed study reveals that the H-2(9/2) -> I-4(15/2) transition at 410 nm involves a three-step process while the other transitions involve two-steps. Excitation with 532 nm radiation gives additional bands at 380, 404, 475 and 843 nm wavelengths due to the (4)G(11/2) -> I-4(15/2) -> P-2(3/2) -> I-4(13/2) -> P-2(3/2) -> I-4(11/2), and S-4(3/2) -> I-4(13/2) transitions, respectively, along with the bands observed on NIR excitation. The fluorescence yield is found to be largest for the TeO2-Na2O glass. The lifetime of the S-4(3/2) level has been measured for all the three cases and used to explain the upconversion mechanisms. The fluorescence intensity ratio corresponding to the two thermally coupled levels (H-2(11/2), S-4(3/2)) has been used to estimate the temperature of the glass. It is observed that the temperature sensing capacity of TeO2-Li2O glass is better than the other two glasses. (c) 2006 Elsevier Ltd. All rights reserved.