Multicolour and up-conversion fluorescence of lanthanide doped Vernier phase yttrium oxyfluoride nanocrystals

Multicolour and up-conversion fluorescent nanocrystals of lanthanide doped orthorhombic yttrium oxyfluorides were prepared via a facile precursor route for the first time. The stepwise fabrication procedure involves room-temperature coprecipitation of Y3+ ions with CO32- and F- in water and subsequent thermal decomposition. Powder X-ray diffraction studies confirmed that all of the undoped and lanthanide ion-doped samples annealed at 400 degrees C were pure Vernier phase adopting an orthorhombic structure. The crystal structure, synthetic details, morphologies, and luminescence properties of the nanocrystals were investigated by means of TEM, thermal and spectroscopic measurements. In the structure, Y atoms occupy four crystalline sites with different coordination by O2-/F-, giving rise to complex environments for the doping of rare earth ions. Green emission bands were observed from the Tb3+ doped samples under UV excitation (lambda(ex) = 284, 377 nm), while the Eu3+ doped nanocrystals exhibited bright red emission upon both UV and blue irradiation (lambda(ex) = 381, 465 nm). Those nanocrystals codoped with Yb3+/Er3+, Yb3+/Ho3+ and Yb3+/Tm3+ show intense red, green and blue up-conversion fluorescence respectively upon irradiation at 980 nm with a diode laser. The Vernier phase yttrium oxyfluoride phosphors have the potential for use in applications such as bioprobes, optical nanodevices, and chromatic displays.