Ultraviolet and violet upconversion fluorescence of europium (III) doped in YF_3 nanocrystals

Under 980 nm excitation, Eu(3+)/Tm(3+)/Yb(3+) tri-doped YF(3) nanocrystals emitted ultraviolet and visible fluorescence. Besides the upconversion emissions from Tm(3+) ions, not only were the unusual (5)D(2)-->(7)F(3), (5)D(3)-->(7)F(J) emissions of Eu(3+) observed, but also the ultraviolet upconversion luminescence of Eu(3+) from (5)H(3-7), (5)G(2-6), (5)L(6)-->(7)F(0) transitions were recorded. This unique optical property was attributed to the bridging function of Tm(3+) ions in populating high-energy states of Eu(3+) ions.