Ultraviolet and visible emissions of Er3+ in monoclinic KYb(WO4)2 single crystals

We observed ultraviolet and visible up-conversion signals with maximum intensity at 383 nm, 407 nm, 457 nm, 474 nm, 525 nm, 552 nm, 652 nm, 696 nm, 772 nm, 801 nm, 814 nm and 848 nm from the 4f states of erbium-doped KYb(WO4)2 single crystals after pumping at 981 nm (10 194 cm−1) at room temperature (RT) and low temperature (10 K). These emissions were generated after simultaneous excitation of erbium and ytterbium at 981 nm (Yb3+ acts as a sensitizer of Er3+). We discuss the up-conversion mechanism in which three and two photons were involved in the generation of the ultraviolet and visible emissions.