Effects of Li+ ions on the enhancement of up-conversion emission in Ho3+-Yb3+ co-doped transparent glass–ceramics containing Ba2LaF7 nanocrystals

• In this paper, the up-conversion (UC) and Stokes emission of Ho3+-Yb3+ and Li+ co-doped transparent glass ceramics 45 SiO2-15 Al2O3-12 Na2CO3-21 BaF3-7 LaF3-0.2 HoF3-YbF3-xLi2CO3 (x = 0, 0.5, 1, 2, 4 and 6 mol%) containing Ba2LaF7 nanocrystals were investigated. These glass ceramics samples were prepared using the conventional quenching techniques.
• The Ba2LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction (XRD). Compared with the glass-ceramics sample without Li+ codoping, the UC and Stokes emission intensity of glass-ceramics samples with Li+ codoping were increased.
• It can be proved that the Li+ can effect the enhancement up-conversion (UC) and Stokes emission. Particularly, the green UC emission intensity band centered at 546 nm was strongly increased twice with the increase of Li+ up tp 4mol%. Through the comparison and analysis of the energy graph, it was shown that the 5F4/5S2 → 5I8 transition of Ho3+ ion in the green (546 nm) region.
• There are two weak fluorescence in the red (657 nm) region and near infrared (753 nm) region of spectrum, which is the 5F4/5S2 → 5I7 and 5F5 → 5I8 transition of Ho3+. Therefore, the Stokes emission results showed that the incorporation of Li+ ions into the Ba2LaF7:Eu3+ lattice could induce a remarkable change of the Stokes emission intensity in red region (R = IED/IMD) with 393 nm excitation wavelength. It was indicated that it improved the effect of Li+ co-doped in Ho-Yb on symmetry of the lattice.
• The possible mechanism responsible for the enhancement of UC and Stokes emission in Ho-Yb co-doped were discussed.

The up-conversion (UC) emission of Ho3+-Yb3+ and Li+ co-doped transparent glass ceramics 45SiO2-15Al2O3-12Na2CO3-21BaF2-7LaF3-0.2HoF3-1YbF3-xLi2CO3 (x = 0, 0.5, 1, 2, 4 and 6 mol%) containing Ba2LaF7 nanocrystals were investigated. These glass ceramics samples were prepared using the conventional quenching techniques. The Ba2LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction (XRD). Compared with the glass ceramics sample without Li+, the UC emission intensity of glass ceramics samples with Li+ were enhanced. It can be proved that the Li+ can affect the enhancement up-conversion (UC) emission. Particularly, the green UC emission intensity band centered at 546 nm was strongly increased twice with the concentration of Li+ increasing up to 4 mol%. Through the comparison and analysis of the energy graph, it was shown that the 5F4/5S2→5I8 transition of Ho3+ ion obtained the green (546 nm) light. There are two weak fluorescences in the red (657 nm) region and near infrared (753 nm) region of spectrum, which is the 5F4/5S2→5I7 and 5F5→5I8 transition of Ho3+. Therefore, the emission results showed that the incorporation of Li+ ions into the Ba2LaF7:Eu3+ lattice could induce a remarkable change of the emission intensity in red region (R = IED/IMD) with 393 nm excitation wavelength. It was indicated that the symmetry of the lattice was destroyed by Li+ in glass ceramics. The possible mechanism responsible for the enhancement of UC emission in Ho-Yb co-doped was discussed.

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