Fluorophosphate Upconversion-Luminescent Glass-Ceramics Containing Ba2LaF7:Er3+ Nanocrystals: An Advanced Solid-State Nuclear Magnetic Resonance Study

Fluorophosphate glass-ceramics containing Ba2LaF7:Er3+ nanocrystal upconversion-luminescent materials were prepared via a melt-quenching method, followed by heat treatment. The glass structure evolution, which was induced by the change in composition, as well as heat treatment, was characterized via solid-state nuclear magnetic resonance (SSNMR) spectroscopy. Multiple Q(mLa)(n) phosphorous species (n and m represent the numbers of P-O-P and P-O-La bonds, respectively) were proved via multiple 31P magic-angle spinning (MAS). Three fluorine species [P-F center dot center dot center dot Na, Ba-F center dot center dot center dot Na, and (Ba, La)-F center dot center dot center dot Na] were resolved using F-19 MAS spectra. Unlike Y3+, La3+ cannot attract F to form an La-F center dot center dot center dot Na linkage in phosphate glasses. Furthermore, dissimilar to the competition behavior between the positive ions to attract F-, the F-19 NMR results demonstrates that Ba2+ and La3+ combined preferentially to attract F-, thus inducing the preferential formation of the (Ba, La)-F center dot center dot center dot Na species, followed by the ultimate precipitation of the Ba2LaF7 crystal after the heat treatment. The paramagnetic effects of Er3+ on F-19 and P-31 indicates that there are still many Er3+ ions in the glass phase after crystallization, even though the Er3+ ions dominated the Ba2LaF7 crystal. The evolution of the P-3(1) spectrum via crystallization indicates that the precipitation of Ba2LaF7 facilitates the polymerization of the phosphorus glass network. Finally, a structural evolution model is developed.

Automated summary

The presence of Ba2LaF7 crystals facilitates the polymerization of the phosphorus glass network, with Er3+ ions still present in the glass phase even after crystal formation, as indicated by the evolution of the P-31 spectrum.