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

Abstract

Solid-state nuclear magnetic resonance (NMR) spectroscopy is used to study heavily Yb3+ and Er3+ doped, fluorescent NaY1–x–y Yb x Er y F4 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.

Probing Surface Effects on α-NaYF4 Nanoparticles by Nuclear Magnetic Resonance

“…Although the β-phase has been more extensively investigated because of its efficient upconversion emission, the cubic α-NaYF 4 NP is postulated as the simplest structure to understand fundamental properties , such as surface effects in the structure. Previous NMR studies , investigated structural properties of undoped and rare earth doped NPs, evaluating the quality of the crystals formed and the influence of the dopant in the crystalline lattice parameter and spin diffusion. Despite the completeness of these studies, no size dependence on the structural properties influenced by surface effects was reported though they are among the fundamental features of nanoscaled materials.…”

Relaxation Processes in Rare-Earth-Doped α-NaYF4 Nanoparticles by Nuclear Magnetic Resonance Spectroscopy

“…The spin−lattice relaxation times (T 1 ) were obtained from the IR-MAS experiments using the intensity-areas for the longitudinal-relaxation analysis (I(τ)) also taken from the integration of the spectra and by fitting the data to the following function ) where I 0 is the equilibrium magnetization and f < 2 accounts for incomplete magnetization inversion after the π pulse. 19 F{ 23 Na} and 23 Na{ 19 F} REDOR experiments were performed in the Agilent DD2 spectrometer, operating at 5.64 T, following the experimental details presented in ref 42. Typical acquisition parameters were: π-pulse lengths of 4.4 and 3.6 μs for 19 F and 23 Na, respectively, recycle delays of 15 s for 19 F and 0.1 s…”

“…19 F{ 23 Na} and 23 Na{ 19 F} REDOR experiments were performed in the Agilent DD2 spectrometer, operating at 5.64 T, following the experimental details presented in ref 42. Typical acquisition parameters were: π-pulse lengths of 4.4 and 3.6 μs for 19 F and 23 Na, respectively, recycle delays of 15 s for 19 F and 0.1 s…”

“…The Journal of Physical Chemistry C for 23 Na observation, MAS at 24 kHz and up to 96 and 256 scans accumulated for each REDOR spectrum, either for 19 F and 23 Na observation. Experimental dipolar second moments (M 2(S−I) ) were obtained from parabolic fits of the initial part of the REDOR curves ΔS/S 0 < 0.2, using the following equation 43,44 S S I I fM NT 1 (…”

“…21,36 Furthermore, NPs of ϕ ≈ 7 nm or those with high size polydispersity are prompt to present distortions due to surface effects and site defects. 36 context, we have prepared RE-doped α-NaYF 4 (from La 3+ to Lu 3+ ) NPs with a moderate doping level (≈2%), about 7 nm diameter and low polydispersity, and characterized their local structure by 23 Na and 19 F high-resolution NMR and magnetic relaxation. We also support our discussion by investigating 1% Lu 3+ -and 1% Gd 3+ -doped NPs.…”