Laser-diode excited intense upconversion luminescence of Er3+ in bismuth--lead--germanate glasses
Laser-diode excited intense upconversion luminescence of Er^3＋ in bismuth-lead-germanate glasses

We have investigated infrared-to-visible upconversion luminescence of Er3+ in bismuth--lead--germanate glasses. The UV cutoff wavelength is shortened while its lifetime is increased almost linearly, with PbF2 substituting for PbO in the bismuth--lead--germanate glasses. Three emissions centred at around 529, 545 and 657nm are clearly observed, which are identified as originating from the 2H11/2\rightarrow ^4{\rm I15/2, 4S3/2\rightarrow 4I15/2 and 4 F9/2\rightarrow 4I15/2 transitions, respectively. It is noted that all the upconversion emission intensities increase with PbF2 concentration increasing. The ratio between the intensities of red and green emissions increases with the increasing of PbF2 content. Energy transfer processes and nonradiative phonon-assisted decays account for the populations of the 2H11/2,4 S3/2 and 4F9/2 levels. The quadratic dependence of fluorescence on excitation laser power confirms a two-photon process to contribute to the upconversion emissions.