Investigation of energy transfer and frequency upconversion in Ho3+/Yb3+ co-doped tellurite glasses

A serials of Ho3+/Yb3+ co-doped tellurite glasses by pumping 970 nm laser diode (LD) were demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Two intense emission bands were observed in Ho3+/Yb3+ co-doped tellurite glasses centered at 549 and 664 nm corresponding to Ho3+: 5S2(5F4)→5I8 and 5F5→5I8 transitions, respectively. The upconversion intensities of red and green emissions in Ho3+/Yb3+ co-doped glasses were enhanced largely when increasing Yb2O3 content. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms had been evaluated by a proper rate equation model. The energy transfer coefficients were estimated by fitting the simulated curves to the measured ones. The obtained three energy transfer coefficients CD2, CD3 and CD4 were CD2=5.0×10−18 cm3/s, CD3=1.5×10−17 cm3/s, CD4=9.0×10−17 cm3/s.