Synthesis and ultraviolet upconversion fluorescence of Tm3+ doped YbF3 microparticles

YbF3 microparticles doped with Tm3+ were synthesised by coprecipitation method, from which intense ultraviolet and blue emission bands are observed under 980 nm excitation. It is found that the upconversion fluorescence intensity of YbF3:Tm3+ synthesised by coprecipitation method is efficiently enhanced comparing with that prepared by solid state reaction method. The dependence of the emission intensity on pumping power was investigated in the Tm3+ doped YbF3. It is believed that two- and three-photon processes perform populations of 1G4 and 1D2 levels of Tm3+ respectively. The dominant upconversion mechanism may be attributed to a cooperative sensitisation process, which makes two Yb3+ ions in excited states cooperatively transfer their energy to a Tm3+ ion. The dependence of the emission intensity on the concentration of Tm3+ was also discussed.