Separation of quadrupolar and paramagnetic shift interactions with TOP‐STMAS/MQMAS in solid‐state lighting phosphors

A new approach for processing satellite‐transition magic‐angle spinning (STMAS) and multiple‐quantum magic‐angle spinning (MQMAS) data, based on the two‐dimensional one‐pulse (TOP) method, which separates the second‐rank quadrupolar anisotropy and paramagnetic shift interactions via a double shearing transformation, is described. This method is particularly relevant in paramagnetic systems, where substantial inhomogeneous broadening may broaden the lineshapes. Furthermore, it possesses an advantage over the conventional processing of MQMAS and STMAS spectra because it overcomes the limitation on the spectral width in the indirect dimension imposed by rotor synchronization of the sampling interval. This method was applied experimentally to the 27Al solid‐state nuclear magnetic resonance of a series of yttrium aluminum garnets (YAGs) doped with different lanthanide ions, from which the quadrupolar parameters of paramagnetically shifted and bulk unshifted sites were extracted. These parameters were then compared with density functional theory calculations, which permitted a better understanding of the local structure of Ln substituent ions in the YAG lattice. A new approach for processing STMAS/MQMAS spectra that permits the separation of the paramagnetic shift and quadrupolar lineshape into orthogonal dimensions is shown. Using this method, we were able to identify and extract quadrupolar coupling parameters of both paramagnetically shifted and unshifted Al environments in a series of lanthanide‐doped yttrium aluminium garnets. The obtained parameters were then compared with density functional theory calculations, which provided valuable insight into the local structure of the substituent ions.