EXAFS study of cation reordering in NaYF4:Yb3+, Tb3+ up-conversion luminescence materials

The NaYF4:Yb3+, Tb3+ (xYb: 0.20, xTb: 0.04) materials were prepared using the co-precipitation method. The as-prepared material was washed either with or without water in addition to ethanol and thereafter annealed for 5 h at 500 °C. This resulted in materials with moderate or very high up-conversion luminescence intensity, respectively. The structural study carried out with X-ray powder diffraction revealed microstrains in the rare earth (R) sublattice that were relaxed for the material with very high up-conversion intensity thus decreasing energy losses. The local structural details were investigated with R LIII and Y K edge extended X-ray absorption fine structure (EXAFS) using synchrotron radiation. Around 10 mol.% of the Yb3+ ions were found to occupy the Na site in the material with very high up-conversion intensity. These Yb species formed clusters with the Tb3+ ions occupying the regular Na/R sites. Such clustering enhanced the energy transfer between Yb3+ and Tb3+ thus intensifying the up-conversion emission.

Distance distributions around Y, Yb and Tb calculated from EXAFS data for Na(Y0.76Yb0.20Tb0.04)F4 with very high up-conversion intensityFigure optionsDownload as PowerPoint slide