Ultraviolet-enhanced upconversion emission mechanism of Tm3+ in YF3:Yb3+, Tm3+ nanocrystals.

Dependences of the spectral profiles on the both Tm(3+)- and Yb3+ additive amounts were presented. Further, the temporal evolution of Tm3+ luminescence in the nanocrystals was explored. Enhanced ultraviolet emissions with Tm3+ upconversion were investigated in the Y(0.800-x)Fa:Yb(3+)0.200, Tm3+(x), nanocrystal samples following excitation with 980 nm. The emissions can be attributed to the transitions of 1G4 --> 3H6, 1D2 --> 3F4 or 3H6 and (3P0 and 1I6) --> 3F4 or 3H6. A detailed energy-transition scheme was proposed and described well the ultraviolet-enhanced upconversion of Tm3+ and the energy-transfer processes from Yb3+ to Tm3+ based on energy-matching conditions.