Upconversion and concentration quenching in Er3+-doped TeO2–Na2O binary glasses

The spectroscopic properties of Er3+-doped alkali tellurite TeO2–Na2O glasses are investigated. Infrared-to-visible upconversion emission bands are observed at 410, 525, 550 and 658 nm using 797 nm excitation wavelength. These bands are assigned to the 2H9/2 → 4I15/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transition, respectively. The power dependence study reveals that the 2H9/2 → 4I15/2 transition involves a three-step process while the other upconversion transitions involve only two steps. An excitation with 532 nm wavelength, two upconversion bands are observed in the UV region at 380 and 404 nm in addition to bands in the visible region at 410, 475, 525, 550, 658 and 843 nm. These bands are ascribed to 4G11/2 → 4I15/2, 2P3/2 → 4I13/2, 2H9/2 → 4I15/2, 2P3/2 → 4I11/2, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, 4F9/2 → 4I15/2 and 4S3/2 → 4I13/2 transition, respectively. Increasing Er3+ concentration leads to a rapid growth in the intensity of red emission relative to that for the green emission. An explanation for this observation has been suggested. The temperature dependence profile for the two thermally coupled levels (2H11/2, 4S3/2) shows that they can be used for measuring the temperature.