Anomalous Anisotropic Dopant Distribution in Hexagonal Yttrium Sublattice

Trivalent lanthanides are commonly incorporated into sodium yttrium fluoride nanocrystals to enhance their optical properties. Lanthanides are expected to randomly replace trivalent yttrium cations due to their isovalent nature, and the dopant-dopant distance decreases with increasing dopant concentration. Combining spectroscopy with quantum mechanical calculations, we find that large lanthanides exhibit an anisotropic distribution in the hexagonal yttrium sublattice at low dopant concentrations. This counter-intuitive substitution suggests the formation of one-dimensional dimers or chains with short dopant-dopant distances. Our study of the distance-sensitive cross-relaxation between Nd3+ dopants in beta-NaYF4 nanocrystals confirms that the concentration quenching threshold is lower than that of their cubic counterparts, consistent with the proposed chain-like model. Moreover, we demonstrate modulation of the anisotropic distribution by microstrain management via alkali metal codoping. Research into dopant distribution in inorganic crystals may enable the development of new materials and properties for future challenges.

Automated summary

Trivalent lanthanides are commonly used in sodium yttrium fluoride nanocrystals to improve their optical properties. At low dopant concentrations, large lanthanides exhibit an anisotropic distribution in the hexagonal yttrium sublattice, suggesting the formation of one-dimensional dimers or chains. Our research indicates that the concentration quenching threshold of beta-NaYF4 nanocrystals is lower than that of their cubic counterparts, and the anistropic distribution can be modulated by microstrain management via alkali metal codoping. Understanding dopant distribution in inorganic crystals may lead to the development of new materials and properties in the future.