Transparent glass-ceramics of sodium lutetium fluoride co-doped with erbium and ytterbium

Transparent sodium lutetium fluoride aluminosilicate glasses and glass-ceramics were prepared by the melting-quenching method. The glasses were doped with 0.5 mol% Er3+ and 0.5Er3+-xYb3+ (x = 2, 4 mol%) to obtain efficient up-conversion (UC) emission, as well as infrared emission at ~ 1.0 and 1.5 μm. After suitable thermal treatment, transparent glass-ceramics with cubic NaLuF4 nanocrystals ranging from 10 to 50 nm were obtained. The crystallization process was investigated using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM). Energy dispersive X-ray (EDX) analysis showed the incorporation of rare-earth (RE) ions into the nanocrystals. The luminescent features of the near-infrared emission spectra of Er3+ and Yb3+ in the co-doped samples demonstrated efficient energy transfer between both ions. The presence of Yb3+ greatly enhanced the UC emission in the co-doped samples and tuned the emission from green to yellow. These effects were more pronounced for the glass-ceramics, confirming the incorporation of RE ions in the nanocrystals. The possible UC processes and mechanisms leading to population of 4S3/2 and 4F9/2 excited levels are discussed.