Upconversion fluorescence of Nd$^{3+}$ ions in K2YF5 single crystal

RADIOCHUpconversion fluorescence of Nd3+ ions in K2YF5 single crystal was studied under 785-nm (near-infrared), 514.5-nm (green) and 325-nm (ultraviolet) laser excitation. With laser excitation set at 785 nm, a near-infrared upconversion emission band centered at 745 nm with a peculiar linear power dependence was observed and explained successfully by using a multiphonon assisted upconversion mechanism. With 514.5-nm laser excitation, five upconversion emission bands centered at 358, 386, 417, 451 and 496 nm were recorded. The power dependence of these emission bands was also studied and the upconversion mechanism was attributed to the excited state absorption from F-4(3/2) state. In addition, the ultraviolet upconversion fluorescence which peaked at 287 nm under 325-nm laser excitation was also presented and analyze