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Doping Characterization by NMR

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Participants :
Sébastien Maron* (thèse), Thierry Gacoin

Work in collaboration with: François Devreux (PMC – Physics of irregular systems group), Géraldine Dantelle (Institut Néel, Grenoble) and Nadège Ollier (Laboratoire des Solides Irradiés, Palaiseau)

Knowledge of the doping paramagnetic level is an important challenge. A lot of phenomena depend of the concentration, e.g. the well-known concentration quenching where the rare-earth luminescence decreases with the concentration above a certain level.1 As model material, we choose LaPO4, synthesized by coprecipitation, where Lanthanum could be substituted by a Rare-Earth element from Cerium to Gadolinium.
In Phys. Chem. Chem. Phys. we showed that we could determine very low doping level if we know the longitudinal nuclear relaxation time T1, with a better accuracy than some classical technique such as the measurement of the unit cell parameters by XRD.2 In fact, in this range of concentration, 1 / T1 obey to a linear law in function of the doping concentration whereas the variation of the unit cell parameter is chaotic and does not respect the Vegard’s law (Figure below). We showed too that the relaxation time depends of the precursors’ mixing. Electronic relaxation times values obtained by ESR at LSI or at INSP (Pierre-et-Marie-Curie University) confirmed our data of nuclear relaxation time.
Some others phosphate materials, amorphous or crystalline, were synthesized and their relaxation time studied for trying to determinate a universal law between T1 and the doping concentration.

Figure 1

1. A. Huignard, V. Buissette, A.-C. Franville, T. Gacoin and J.-P. Boilot, The Journal of physical Chemistry B ,2003, 107, 6764-6759.
2 S. Maron, G Dantelle, T. Gacoin and F. Devreux, Physical Chemistry Physics 2014,16,18788-18798.