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Tuning color output and enhancing upconversion emission of Er3+ ions in transparent sodium lutetium fluoride glassceramics in bulk and optical fibers, by adjusting the Yb3+ doping level and the excitation power, has been demonstrated. The addition of Yb3+ enhances the UC emission and tunes the color from green to yellow due to an increase of the red-to-green intensity ratio. Moreover, the relative emission intensities of blue, green, and red emissions can be changed by controlling the excitation power which tunes the color from yellow to green.

[EN] Novel glass-ceramic optical fibers containing NaLuF nanocrystals doped with 0.5ErF and 2YbF (mol%) have been prepared by the rod-in-tube method and controlled crystallization. NaLuF nanocrystals with a size around 20 nm are obtained after heat treatment at 600 °C. Intense upconverted green and red emissions due to (H, S) → I and F → I transitions, respectively, together with a blue emission due to H → I transition have been observed under excitation at 980 nm. The intensity of the green and red upconversion bands shows a nearly linear dependence on the excitation power which can be explained by saturation effects in the intermediate energy states and proves that a sensitized energy transfer upconversion process is responsible for the population of the emitting levels of Er ions. The upconversion emission color changes from yellow to green by increasing the excitation power density which allows to manipulate the color output of the Er emission in the glass-ceramic fibers. The tunable emission color is easily detected with the naked eye. This interesting characteristic makes these glass-ceramic fibers promising materials for photonic applications.

In this work, the study of the near infrared to visible upconversion (UC) emission in transparent sodium lutetium fluoride glass-ceramics doped with ErF 3 and co-doped with YbF 3 is reported. Intense UC green and red emissions due to ( 2 H 11/2 , 4 S 3/2 ) →4 I 15/2 and 4 F 9/2 →4 I 15/2 transitions respectively together with a more weak blue emission due to the 2 H 9/2 →4 I 15/2 transition have been observed under excitation at 980 nm. The influence of Yb 3+ co-doping and excitation power density on the upconversion emissions is investigated. The addition of Yb 3+ ions greatly enhances the overall UC emission intensity and can be used to tune the UC emission from green to yellow due to an increase of the red-to-green ratio.

Transparent oxyfluoride glass-ceramic fibers containing Nd3+doped- LaF3 nano-crystals were drawn using single crucible method and crystallized before cladding deposition. Optical fibers with Nd-NaGdF4 were also prepared by double crucible method with AR glass cladding. The fibers were characterized from a structural and optical point of view.