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

Abstract

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.