(169e) Quantitative Spatial Distribution of Rare Earth Dopants in NaGdF4 Nanoparticles

Exploring distribution of rare earth dopants within nanoparticles are crucial to understand the relationship between dopants and their optical properties, and thusly to rationally improve and optimize their optical properties. Energy dispersive X-ray spectroscopy (EDS) element mapping is the well accepted method to map out the distribution of the dopants within the nanoparticles. Firstly, EDS line mapping provides a two dimensional and depth-averaged qualitative distribution of the dopants in the nanoparticles and, secondly, the mapping is only done on few selected nanoparticles which might not represent the distribution within all the nanoparticles. Here, we employ anomalous small angle X-ray scattering (ASAXS) measurements to quantitatively measure the three-dimensional distribution of Yb³⁺/Y³⁺/Lu³⁺ in NaGdF₄. These measurements revealed a radial gradient distribution of dopants (Yb³⁺/Y³⁺/Lu³⁺) from the core to the outer edges of the NaGdF₄ nanoparticles. Moreover, shells with the same dopant species and concentration were epitaxially grown on Yb³⁺-doped sample (NaGdF₄:18%Yb,2%Er, denoted as Gd:Yb) to synthesis core/shell (Gd:Yb@Gd:Yb) and core-shell-shell (Gd:Yb@Gd:Yb@Gd:Yb) samples. We discovered heterogeneous distribution of ytterbium ionswithin the shell-regions. The overall features of the distribution of the sensitizer ions in the host matrix obtained from detailed ASAXS analyses were also qualitatively confirmed by independent EDS measurements. These findings are useful for rationalizing shell-dependent emission properties, understanding the emission mechanisms in complex core/shell nanostructures, and for creating models for multifunctionality and optimal performance in applications.