Abstract
Generation of near-infrared light within the first biological optical window via frequency upconversion in Tm3+-doped PbGeO3-PbF2-CdF2 glass excited within the second biological window at 1.319 μm is reported. The upconversion emission at 800 nm is the sole light signal observed in the entire ultraviolet-visible-near-infrared spectral region making it possible obtaining high contrast imaging. The dependence of the 800 nm signal upon the sample temperature was investigated and results showed an increase by a factor of ×2.5 in the 30–280 °C range. Generation of detectable 690 nm for temperatures above 100 °C in addition to the intense 800 nm main signal was also observed. The proposed excitation mechanism for the 800 nm thulium emitting level is assigned to a multiphonon-assisted excitation from the ground-state 3H6 to the 3H5 excited-state level, a rapid relaxation to the 3F4 level and followed by an excited-state absorption of the pump photons mediated by multiphonons connecting the 3F4 level to the 3H4 emitting level.
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