Blind spheres of paramagnetic dopants in solid state NMR

Abstract

Paramagnetic dopants make the NMR spectroscopist go blind in a sphere around a paramagnetic ion. How big is the blind zone?

A Guide to Brighter Phosphors‐Linking Luminescence Properties to Doping Homogeneity Probed by NMR

“…The resulting peak areas from one pulse experiments were calculated and tested by the visibility function . Deviations from the theoretical visibility function for homogeneous doping indicate a lower degree of NMR homogeneity.…”

“…As the doping level x increases, the signal broadens without significant shifts and the peak area decreases ( 31 P MAS NMR spectra stack plots in Supporting Information Figure S6–S11). Thus the situation in the investigated cases is simpler than in the cases of La 1‐ x Sm x PO 4 and La 1‐ x Eu x PO 4 , where different 31 P signals could be observed.…”

“…[17][18][19][20]26,35,36] The NMR visibility is defined as the visible signal of the doped material normalized by the signal of the diamagnetic host. [35] For a homogeneous doping scenario, the NMR signals vanish in the dead-time of the spectrometer [36] more efficiently thus f(x) approaches zero earlier as x increases. The visibility of the heterogeneous case f(x) is located in the dashed regime between the maximum visibility f max (x) (upper solid line) and the visibility of a homogeneous doping scenario.…”

“…The resulting peak areas from one pulse experiments were calculated and tested by the visibility function. [35,36] Deviations from the theoretical visibility function for homogeneous doping indicate a lower degree of NMR homogeneity. By this comparison for seven Ln 3 + dopants (Figure 4 for Dy 3 + and for other Ln 3 + ions (Supporting Information Figure S6-S11)) it is possible to conclude that the samples series obtained via a solid-statereaction showed a lower degree of NMR homogeneity as compared to the co-precipitated samples of the same dopant series.…”

“…In terms of luminescence the radii of these spheres (big circles) could be interpreted as the critical energy transfer distance R c . The radii r 0 and R c are not the same but typical values fall into a similar range: Å – few nm …”