We report the infrared-to-visible upconversion luminescence of Er<sup>3+</sup>-doped lead–niobium–germanate glasses (GeO<sub>2</sub>–PbO–Nb<sub>2</sub>O<sub>5</sub>) with different Er<sub>2</sub>O<sub>3</sub> concentrations (0.5, 1, 2, and 3 wt.%) under continuous-wave and pulsed-laser excitation in the near-infrared region inside the <sup>4</sup>I<sub>9/2</sub> level. Intense green emission due to the (<sup>2</sup>H<sub>11/2</sub>, <sup>4</sup>S<sub>3/2</sub>)→<sup>4</sup>I<sub>15/2</sub> transitions was observed at room temperature together with a weak red emission corresponding to the <sup>4</sup>F<sub>9/2</sub>→<sup>4</sup>I<sub>15/2</sub> transition. These upconversion emissions are attributed to a two-photon process. The time evolution of the green emission from the <sup>4</sup>S<sub>3/2</sub> level indicates that energy-transfer upconversion and excited-state absorption are responsible for the upconversion luminescence. The increase of the weak red emission with increasing Er<sub>2</sub>O<sub>3</sub> concentration, together with its temporal behavior under infrared excitation, suggests that for Er<sub>2</sub>O<sub>3</sub> concentrations higher than 1 wt.%, the upconverted red emission is the result of multiphonon relaxation from the <sup>4</sup>S<sub>3/2</sub> level and energy-transfer processes.
© 2004 Optical Society of America
(160.2750) Materials : Glass and other amorphous materials
(160.4670) Materials : Optical materials
(160.5690) Materials : Rare-earth-doped materials
(190.7220) Nonlinear optics : Upconversion
(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence
Rolindes Balda, Angel J. Garcia-Adeva, Joaquin Fernández, and José M. Fdez-Navarro, "Infrared-to-visible upconversion of Er3+ ions in GeO2–PbO–Nb2O5 glasses," J. Opt. Soc. Am. B 21, 744-752 (2004)