Enhancement of the upconversion luminescence intensity in Er3+ doped BaTiO3 nanocrystals by codoping with Li+ ions

Infrared-to-visible upconversion luminescence spectra were investigated in Er3+ doped and Er3+–Li+ codoped BaTiO3 nanocrystals following excitation with 976 nm. By introducing Li+ ions, the upconverted emission intensity is found to be greatly enhanced compared to that of the nanocrystals without Li+ ions. The enhanced luminescence might be attributed to the oxygen vacancy generated by Li+ ion incorporation in the lattices and the distortion of the local asymmetry around Er3+. We observe that excitation power dependence and decay time are increased by the incorporation of Li+ ions. Li+ ions also can reduce the OH groups in specimen, which decrease nonradiative decay from the 4S3/2 to 4F9/2, enhancing the upconversion emission intensities.

Research highlights
► Li+ strongly enhanced upconversion luminescence intensity of Er3+–Li+ codoped BaTiO3.
► Li+ changed the local symmetry around Er3+.
► Excitation power dependence and decay time were increased by Li+ ions.
► OH groups in specimen were decreased by Li+ ions.