Efficient continuous wave laser operation of Tb3+-doped fluoride crystals in the green and yellow spectral regions

In this work Tb3+ is revisited as a laser ion for efficient visible laser operation. In detailed spectroscopic investigations of absorption and fluorescence properties we reveal, that neither the spin-forbidden transitions nor the widespread belief of excited state absorption or upconversion into 4f(7)5d(1)-states ultimately prevent efficient visible laser operation in Tb3+-doped fluorides. In contrast, the rise of blue semiconductor-based pump sources enabled us to achieve slope efficiencies up to 58% around 545 nm in the green spectral region in highly Tb3+-doped LiLuF4, LiYF4, KY3F10, beta-BaLu2F8 and LaF3 crystals. In addition, we obtained laser emission from Tb3+ in the yellow spectral region around 585 nm with slope efficiencies approaching 20%. To the best of our knowledge, these results represent the first continuous wave laser operation of Tb(3+)doped crystals and demonstration of laser oscillation on the D-5(4) -> F-7(4)-transition in this ion.