EFFICIENT GREEN UPCONVERSION EMISSION IN TRANSPARENT TEO2-GEO2 GLASS-CERAMIC OBTAINED BY BILLET EXTRUSION.

Transparent Yb³⁺/Er³⁺ glass-ceramic was successfully obtained by the extrusion method. The extrusion of oxyfluoride tellurite-germanate glass co-doped with Yb³⁺ and Er³⁺ ions at 520 ℃ resulted in the formation of Ba_0.75Er_0.25F_2.25 nanocrystals, leading to an increase in the upconversion (UC) emission intensity of 35 times in glass-ceramic with respect to the glass. The glass to glass-ceramic transition was confirmed by X-ray diffraction (XRD) and Transmission electron microscope (TEM). Also, the structural changes that occurred during crystallization were assessed using Fourier-transform infrared (FTIR) spectroscopy. Furthermore, the pump power and temperature UC emission dependence of glass and glass-ceramic under 976 nm laser excitation were investigated in detail. The assessments showed that i) two-phonons are involved in the UC process and ii) the temperature has a significant influence over it. The Yb³⁺/Er³⁺ codoped glass-ceramic shows relatively high S_a and S_r values in a wide temperature range from 300 to 573 K, presenting the maximal S_a value of 3.50 × 10^-3 at 573 K and the maximal S_r value of 6.30 × 10^-3 at 364 K. These results suggest that the glass-ceramic is a good candidate for optical applications such as luminescent thermometry. [ABSTRACT FROM AUTHOR]