Abstract
In this work we report the optical properties and upconversion luminescence of Er3+ ions in TeO2-WO3-PbO-BaF2 and TeO2-TiO2-Nb2O5-BaF2 fluorotellurite glasses and their comparison with those of TeO2-TiO2-Nb2O5 glass. The optical properties of Er3+ ions have been established in terms of absorption and emission spectra and lifetime measurements. The 1.5 mu m emission cross-section has been determined from the line shape of the emission spectrum and the calculated emission probability for the I-4(13/2) level. The highest emission cross section (6.9 x 10(-21) cm(2)) corresponds to the TeO2-TiO2-Nb2O5-BaF2 glass with a figure of merit for the bandwidth of 524.4 cm(2) nm. Upconversion emissions at 530, 548 nm, and 660 nm have been obtained under infrared excitation at 800 nm in the I-4(9/2) level and compared with those obtained under one photon excitation. The green emission corresponding to the S-4(3/2) - I-4(15/2) transition is dominant in all glasses. The excitation wavelength dependence of the upconverted luminescence together with its time evolution after infrared pulsed excitation suggest that energy transfer upconversion processes are responsible for the green upconversion luminescence. (C) 2011 Elsevier B.V. All rights reserved.