Yb3+ Ions Distribution in YAG Nanoceramics Analyzed by Both Optical and TEM-EDX Techniques

We show the approach in the structural and spectroscopic analysis of Yb3+-doped YAG nanoceramics prepared using 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 8 GPa for sintering is characterized by the highest transparency and confirms the Y3Al5O12 garnet structure of the grains of similar to 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 co-operative 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 4 K and room temperature with the F-2(7/2) -> F-2(5/2) 0-phonon absorption line located 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 nonradiative transitions and conclude that this line might be assigned to Yb3+ distorted sites on the grain surfaces.