51V-NMR and (51)T(1)(T) of charge ordering and spin gap in alpha'-NaV(2)O(5).

We report the interpretation of the first (51)V data on the low-temperature phase of alpha'-NaV(2)O(5) which presents more than two vanadium valences and compare the data to structural models. The influence of the dependence of the line positions on very small amounts of Na substitution by Ca and Li is reported and discussed. The doping and orientation dependence of the spin gap as seen by (51)T(1) is documented, the evidence points towards a significant anisotropy in the nature of the gap which is sensitive to doping.