Germanate-based oxyfluoride transparent glass-ceramic embedded with Tm3+:Ca2YbF7 nanocrystals for high-performance optical thermometer

Germanate-based oxyfluoride transparent glass-ceramic functionalized by Tm3+:Ca2YbF7 nanocrystals was newly developed. The tremendously enhanced upconversion emission of 3F2,3 energy levels by in situ crystallization was extremely beneficial for constructing optical thermometry involving the indirect thermally coupled energy levels (1G4 and 3F2,3) of Tm3+ ions. Utilizing the fluorescence intensity ratio technique, the thermometry po-tentials of PG and GC8 were systematically evaluated based on the emissions from 3F2,3 and 1G4 energy levels. The relative and absolute sensitivities, thermometry resolutions, and repeatabilities were superior to many re-ported materials. This work provides an avenue for precipitating ternary fluoride nanocrystals containing rare earths in germanate-based oxyfluoride glass, and proposes a promising way to achieve high performance optical thermometry based on the emissions from widely spaced energy levels.