We show our approach in the structural and spectroscopic analysis of Yb3+-doped YAG nano-ceramics prepared by the low temperature-high pressure sintering technique (LTHP) by conjugation of both TEM-EDX and optical techniques. Pressure sintering dependences of absorption, emission and decays are analyzed and interpreted. The sample pressurized at 8GPa for sintering is characterized by the highest transparency and confirms the Y3Al5O12 garnet structure of the grains of ∼21 nm average size. Yb3+ ion distribution has been analyzed by both TEM-EDX evaluation in grains and grain boundaries and spectroscopy of Yb3+ pairs of small population from the cooperative luminescence phenomenon. EDX analysis at the TEM scale provides unambiguous results on a clear tendency of almost uniform Yb3+ distribution. An important new observation has been made at 4K and room temperature with the2F7/2 →2 F5/2 0-phonon absorption line at 975.7 nm in addition of the 0-phonon line of the YAG structure of grains at 968 nm similar to that of bulky YAG single crystals. We have discussed the origin of this new 0-phonon line relaxing only by non-radiative transitions and conclude that this line might be assigned to Yb3+ distorted sites on the grain surfaces. © Springer Science+Business Media Dordrecht 2015.