Upconversion properties of a transparent Er³⁺-Yb³⁺ co-doped LaF₃-SiO₂ glass-ceramics prepared by sol-gel method

Transparent 0.1ErF₃-0.1YbF₃-5LaF₃-94.8SiO₂ (mol%) glass-ceramics was prepared by sol-gel method. Efficient upconversion emissions at 379, 407, 450, 490, 520, 540 and 660 nm were observed under 973 nm excitation. The signal at 379 nm is only ∼4.5 times weaker than the signal at 520 nm, that is readily visible by the naked eyes even with a pump power of ∼27 mW, indicating that this sample is a very good infrared-to-ultraviolet upconverter. The data obtained from transmission electron microscopy and X-ray diffraction studies indicate that the rare-earth ions were partitioned in the low phonon energy LaF₃ nanocrystals embedded in silica glass. The analysis of the dynamics of the upconversion emissions from level ⁴S_3/2 (∼540 nm) and level ⁴F_9/2 (∼660 nm) of Er³⁺ suggest that distinct energy transfer excitation pathways are responsible for populating these luminescent levels.