Rare earth ions (REIs) doped oxyfluoride glass-ceramic materials, with their low phonon energy and intensive upconversion luminescent properties, have garnered extraordinary attention in bio-imaging, photovoltaic devices, optical communications, three-dimensional displays and temperature sensing.

Up to now, most researches focus on luminescent performances of oxyfluoride glass ceramics containing various crystalline phases. Both the crystallization mechanism and luminescent performances of glasses are highly dependent on the microstructures of them. However, the microstructures of oxyfluoride glasses remain poorly understood, although there is a growing consensus that a clear understanding of them are critical in developing novel oxyfluoride glass-ceramic materials. Most of the works hitherto are discussions at the macro-level.

Recently, researchers from Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences (SIOM, CAS) have reported a comprehensive structural study of the aluminosilicate oxyfluoride glass ceramics containing Er³⁺: CaF₂ nanocrystals. The results were published in The Journal of Physical Chemistry C.

In the experiment, using multiple solid-state nuclear magnetic resonance (SSNMR) techniques and luminescent spectra, they first reported how the local structures of oxyfluoride glasses were reorganized at the atomic level during the crystallization of fluorides.

Following this, the widely concerned matters, such as the local structures of REIs, the distribution of REIs in the glass and glass ceramics, the way that REIs and Al³⁺ ions affect the crystallization, and the evolution of F- ions local chemical environments, were clearly revealed.

The role of each positive ion during the crystallization and the microcrystallization mechanism of the glasses were first clearly shown on the basis of a comprehensive study of glass-to-crystal structural evolution of these glasses at the atomic level.

The ¹³⁹La NMR signals in glasses and glass ceramics were first acquired in this work by a state-of-the-art SSNMR technique, WURST-CPMG, which will trigger the structural study of lanthanide in glass materials using La³⁺ as a mimic of paramagnetic REIs.

These findings are not only important for understanding the crystallization mechanism at the atomic level, but also present a novel profound investigation strategy of the structure-crystallization-property correlation for oxyfluoride glass ceramics.

This work was supported by the National Nature Science Foundation of China.

Structrual evolution of Er³⁺: CaF₂ crystallization (Image by SIOM)