Intense green and red upconversion emissions from Ho3+ in presence of Yb3+ in Li:TeO2 glass

Weak visible emission is observed at 545 nm and 660 nm on 976 nm excitation of Ho3+ ions doped in tellurite glass. Addition of ytterbium to the doped glass causes a large increase in intensity of the green and the red emissions. In addition to these two new emissions of Ho3+ one in the blue and the other in the NIR region are also observed. This increase in intensity is ascribed to energy transfer from ytterbium ions to holmium ions. Rate equation model has been proposed to study the upconversion emission and its dependence on pumping power. Possible upconversion mechanisms for these emissions are also discussed. Effect of changing the concentration of Yb3+ on the emission intensity, lifetime and full width at half maximum (FWHM) in 5F4(5S2) → 5I8 transition of Ho3+ in codoped sample has also been studied.