The luminescence properties of Er 3+ doped alkali tellurite [ TeO 2 –M 2 O (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 2 H 9/2 → 4 I 15/2 , 2 H 11/2 → 4 I 15/2 , 4 S 3/2 → 4 I 15/2 , 4 F 9/2 → 4 I 15/2 transitions of Er 3+ respectively. Detailed study reveals that the 2 H 9/2 → 4 I 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 → 4 I 15/2 , 2 P 3/2 → 4 I 13/2 , 2 P 3/2 → 4 I 11/2 , and 4 S 3/2 → 4 I 13/2 transitions, respectively, along with the bands observed on NIR excitation. The fluorescence yield is found to be largest for the TeO 2 –Na 2 O glass. The lifetime of the 4 S 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 ( 2 H 11/2 , 4 S 3/2 ) has been used to estimate the temperature of the glass. It is observed that the temperature sensing capacity of TeO 2 –Li 2 O glass is better than the other two glasses.