β-Na(Y1.5Na0.5)F6:Tm3+—A blue upconversion phosphor

A luminescent material β-Na(Y1.5Na0.5)F6 doped with Tm3+ was synthesized by a solid-state reaction method for a steady phosphor of blue upconversion. Under the 671 nm laser excitation, the green emission band of 511 nm due to the 1D2→3H5 transition is obtained for the first time, while the ultraviolet emission band is also observed at 368 nm, associated with the 1D2→3H6 transition. Especially, a wide band of blue emissions is obtained at the wavelength region of 440–490 nm, originated mainly from the 1D2→3F4 (450 nm) and 1G4→3H6 (471–487 nm) transitions, which have potential application in tunable solid-state blue laser of Tm3+. The upconversion mechanism is explored in terms of the energy-level structures of Tm3+ ion and the power dependence of upconverted emission intensity, which is believed to be performed by excited-state absorption.