Infrared-to-visible upconversion of Er 3+ ions in GeO 2 –PbO–Nb 2 O 5 glasses

We report the infrared-to-visible upconversion luminescence of Er3+-doped lead–niobium–germanate glasses (GeO2–PbO–Nb2O5) with different Er2O3 concentrations (0.5, 1, 2, and 3 wt.%) under continuous-wave and pulsed-laser excitation in the near-infrared region inside the 4I9/2 level. Intense green emission due to the (2H11/2, 4S3/2)→4I15/2 transitions was observed at room temperature together with a weak red emission corresponding to the 4F9/2→4I15/2 transition. These upconversion emissions are attributed to a two-photon process. The time evolution of the green emission from the 4S3/2 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 Er2O3 concentration, together with its temporal behavior under infrared excitation, suggests that for Er2O3 concentrations higher than 1 wt.%, the upconverted red emission is the result of multiphonon relaxation from the 4S3/2 level and energy-transfer processes.