FREQUENCY UPCONVERSION FLUORESCENCE OF Er 3+ -DOPED TeO 2-WO3 GLASS

4 I 15/2, 4 S 3/2→ 4 I 15/2 and 4 F 9/2→ 4 I 15/2 transitions of Er 3+ , were observed under 977 nm excitation. The dependence of upconversion intensities on excitation power presents two photon absorption processes for the three emission bands. The upconversion mechanism is discussed, and the dominant mechanisms are excited state absorption and energy transfer upconversion. The intense frequency upconversion fluorescence of Er 3+ -doped TeO2–WO3 glass may be a potential material for developing upconversion fiber optical devices.