Energy transfer and upconversion luminescence in Tm3+/Yb3+ co-doped lanthanum-zinc-lead-tellurite glasses

A series of Tm3+/Yb3+ co-doped lanthanum-zinc-lead-tellurite (TPZL) glasses pumped by a 980 nm laser diode (LD) were demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Effects of PbO content on the thermal stability, structure and upconversion properties of Tm3+/Yb3+ co-doped TPZL glasses had been investigated. The efficient visible upconversion fluorescences corresponding to the 1G4→3H6, 1G4→3F4 and 3H4→3H6 transitions of Tm3+ were observed under 980 nm excitation. The upconversion intensities of blue, red and near infrared emissions in Tm3+/Yb3+ co-doped TPZL glasses were obviously enhanced with increasing PbO content. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms had been evaluated by a proper rate equation model. Population density in different levels and coefficients of the energy transfer rate CDi (i=2, 4, 6) between Tm3+ and Yb3+ were estimated by fitting the simulated curves to the measured ones. The obtained three energy transfer coefficients CD2, CD4, and CD6 were determined to be 5.7x10-17, 1.3x10-16 and 8.6x10-17 cm3/s, respectively