Distribution of Eu3+ ions in LaPO4 nanocrystals

The luminescence spectroscopy of Eu3+ ions in nanocrystal LaPO4 is investigated. The distribution of Eu3+ ions and defects in the LaPO4 nanocrystal host are revealed by different excitation processes. When exciting the Eu–O charge transfer state, the fluorescence emission spectra show distinct sharp lines that indicate the presence of the crystallographic Eu sites in nanocrystalline LaPO4; when directly exciting the Eu3+ intra-4f level transitions, the emission spectra exhibit broad features and a change of the spectral intensity pattern, which are attributed to the presence of a disordered phase and the defects due to the surface effect of the nanocrystal. Two different sizes of LaPO4:Eu3+ nanocrystals, whose particle sizes are 5 and 40 nm, respectively, are studied in this work. In these two nanocrystal samples, the main crystallographic Eu3+ site exhibits the same site symmetry as that in bulk materials. While the Eu3+ ions in the disordered phase distinguish their presence by an obvious contribution to the emission in the 40 nm sample, a strong defect emission dramatically increases its dominance in the spectra, as the particle size decreases to 5 nm.