Upconversion emission enhancement in Er3+/Yb3+-codoped BaTiO3 nanocrystals by tridoping with Li+ ions

Er3+/Yb3+/Li+-tridoped BaTiO3 nanocrystals were prepared by a sol–gel method to improve the upconversion (UC) luminescence of rare-earth doped BaTiO3 nanoparticles. Effects of Li+ ion on the UC emission properties of the Er3+/Yb3+/Li+-tridoped BaTiO3 nanocrystals were investigated. The results indicated that tridoping with Li+ ion enhanced the visible green and red UC emissions of Er3+/Yb3+-codoped BaTiO3 nanocrystals under the excitation of a 976nm laser diode. X-ray diffraction and decay time of the UC luminescence were studied to explain the reasons of the enhancement of UC emission intensity. X-ray diffraction results gave evidence that tridoping with Li+ ion decreased the local symmetry of crystal field around Er3+, which increased the intra-4f transitions of Er3+ ion. Moreover, lifetimes in the intermediate 4S3/2 and 4I11/2 (Er) states were enhanced by Li+ ion incorporation in the lattice. Therefore, it can be concluded that Li+ ion in rare-earth doped nanocrystals is effective in enhancing the UC emission intensity.