Laura Pihlgren

Preparation and Characterization of Nanocrystalline ZrO2:Yb3+,Er3+ Up-conversion Phosphors

Nanocrystalline up‐converting phosphors with zirconium oxide (ZrO2) as the host lattice were prepared with combustion and sol–gel methods. Impurities were analyzed with Fourier transform infrared (FT‐IR) spectroscopy. Yb3+ absorption was studied in the wave number region 10,000–11,500 cm−1 at room temperature and at 10 K. The whole‐blood absorption was measured in the region 9100–41,600 cm−1 at room temperature. Up‐conversion luminescence was excited at room temperature with an IR‐laser at 977 nm. The up‐conversion luminescence spectra showed red (650–685 nm) and green emission (520–560 nm) due to the 4F9/2 → 4I15/2 and (2H11/2, 4S3/2) → 4I15/2 transitions of Er3+, respectively. The materials prepared with combustion synthesis were found to yield the most efficient up‐conversion intensity and the longest luminescence decay.

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.