Tunable upconversion emission in NaLuF4-glass-ceramic fibers doped with Er3+ and Yb3+

In this work, we report the influence of the excitation power density on the upconversion emission of Er3+ ions in novel glass-ceramic optical fibers containing NaLuF4 nanocrystals codoped with 0.5ErF3 and 2YbF3 (mol%) prepared by the rod-in-tube method and controlled crystallization. Intense upconverted green and red emissions due to (2H11/2,4S3/2)→4I15/2 and 4F9/2→4I15/2 transitions, respectively, together with a blue emission due to 2H9/2→4I15/2 transition has been observed under excitation at 980 nm. The upconversion emission color changes from yellow to green by increasing the excitation power density which allows to manipulate the color output of the Er3+ 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.