Energy transfer and frequency upconversion in Ho~(3+)/Yb~(3+) co-doped bismuth-germanate glasses

摘要

We report an intense room-temperature green and red upconversion in Ho~(3+)/Yb~(3+) co-doped xBi_2O_3-(90 -x)GeO_2-10Na_2O glasses upon excitation with a convenient 980 nm laser diode. Effect of Bi_2O_3 on upconversion properties of Ho~(3+)/Yb~(3+) co-doped bismuth-germanate glasses have been investigated based on IR spectra. We find that the increase of Bi_2O_3 decreasing the phonon energy of host glasses. The upconversion intensity of green and red emissions in Ho~(3+)/Yb~(3+) co-doped glasses is enhanced largely with increasing Bi_2O_3 content. Three intense emission bands were observed in Ho~(3+)/Yb~(3+) co-doped BGN glasses centered at 549, 644 and 750 nm correspond to Ho~(3+): ~5S_2(~5F_4) -> ~5I_8, ~5F_5 ->~5I_8 and ~5S_2(~5F_4) ->~5I_7 transitions, respectively. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms had been evaluated by a proper rate equation model.