1.319 μm excited intense 800 nm frequency upconversion emission in Tm~(3+) -doped fluorogermanate glass

摘要

Generation of near-infrared light within the first biological optical window via frequency upconversion in Tm~(3+)-doped PbGeO_3-PbF_2-CdF_2 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 ℃ range. Generation of detectable 690 nm for temperatures above 100℃ 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 ~3H_6 to the ~3H_5 excited-state level, a rapid relaxation to the ~3F_4 level and followed by an excited-state absorption of the pump photons mediated by multipho-nons connecting the ~3F_4 level to the ~3H_4 emitting level.