Crystal growth, optical and spectroscopic characterisation of monoclinic KY(WO4)2 co-doped with Er3+ and Yb3+

We grew un-doped KY(WO4)2 (hereafter KYW), Er3+ and Yb3+ single-doped KYW and Er3+, Yb3+ co-doped KYW single crystals at several dopant concentrations by the Top-Seeded Solution Growth slow-cooling method (TSSG). We studied several optical properties of the host (the transparency window, the orientation of the principal optical axes and the measurement of the refractive indices as a function of the wavelength). We also analysed the spectroscopy of Er3+ and Yb3+ ions in KYW in terms of the optical absorption at room temperature (RT) and at low temperature (6 K), and the luminescence at RT and 10 K in the 1425–1650 nm range corresponding to the 1.5 μm emission of Er3+ (4I13/2 → 4I15/2 transition), after pumping at 981 nm (overlap in energy between 4I11/2 and 2F5/2 levels of Er3+ and Yb3+, respectively) and at 798 nm (4I9/2 level of Er3+). Luminescence was studied in terms of optical emission and lifetimes measurements.