Ion–ion interactions in β-NaGdF4:Yb3+,Er3+ nanocrystals – the effect of ion concentration and their clustering

Abstract

In this work we report co-thermolysis as a suitable method for nanomaterial synthesis which allows the creation of hexagonal upconverting nanocrystals, NaGdF₄:Yb³⁺,Er³⁺, in a wide range of sizes (20–120 nm). Only a very high Yb³⁺ concentration (above 70%) results in pure cubic-phase nanocrystals with irregular shape. Additionally, we showed that the impact of Yb³⁺, Er³⁺ and Gd³⁺ ions on the size and optical properties of nanocrystals is significant. We found that the main changes in optical properties do not depend on the nanocrystal size mostly, but are determined by the ion–ion interactions which include both Er³⁺–Er³⁺ and Er³⁺–Yb³⁺ cross relaxation.