Direct imaging of inhomogeneous distribution of Er3 + ions in lead fluoride nanocrystals

Er3 +-doped lead fluoride nanocrystals (NCs) were precipitated in glasses by heat treatment at 490 °C, and the distribution of Er3 + ions inside the NCs was investigated using electron energy loss spectroscopy. Nucleation started with the formation of 2–4-nm-diameter NCs highly enriched in Er3 +. With further heat treatment, NCs with inhomogeneous Er3 + distribution grew. Crystal structure in individual fluoride NCs changed from tetragonal to cubic due to the variation in Er3 + concentration.