Using NMR Relaxometry to Probe Yb³⁺–Er³⁺ Interactions in Highly Doped Nanocrystalline NaYF₄ Nanostructures

Solid-state nuclear magnetic resonance (NMR) spectroscopy is used to study heavily Yb3+ and Er3+ doped, fluorescent NaY1–x–yYbxEryF4 nanoparticles. An understanding of the 19F wide line NMR response suggests that the 0 ppm portion of the 19F NMR spectrum can be used as a probe of trivalent lanthanide content via spin–lattice relaxation time changes. A Yb3+ and Er3+ magnetic interaction is manifest as a cooperative contribution to the 19F spin–lattice relaxation rate in heavily co-doped nanoparticle samples. The results from this study will aid in the understanding of the mechanism of enhanced optical up-conversion among these well-known nanostructures