There is a need to investigate the possible improvements of rare earth ion-doped transparent ceramics in terms of better optical performances for lasers, scintillators and phosphors. Especially, the spatial distribution of the rare earth ions within their host material is important for quenching processes. Results from Transmission Electron Microscopy (TEM, both conventional and high resolution TEM) and EDX (energy dispersive X-ray) quantitative chemical analysis positively show that there is no significant segregation of Yb3+ ions, the last active rare earth element, in the grain boundaries of Yb3+-doped YAG and Yb3+-doped Y2O3 polycrystalline ceramics. The large value of the Yb3+ segregation coefficient (1.09 in YAG ceramic) explains the homogeneity of this distribution, in opposition to the low values of the Ce3+ and Nd3+ segregation coefficients, the first active rare earth elements, (0.08 and 0.18 respectively in YAG ceramic), which leads to a strong segregation at grain boundaries.
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