Pulsed laser ablation has proved its reliability for the synthesis of nano-particles and nano-structured materials, including metastable phases and complex stoichiometries. The possible nucleation of the nanoparticles in the gas phase and their growth has been little investigated, due to the difficulty of following the gas composition as well as the thermodynamic parameters. We show that such information can be obtained from the optically active plasma during its short lifetime, only a few microseconds for each laser pulse, as a result of a quick quenching due to the liquid environment. For this purpose, we follow the laser ablation of an α-Al2O3 target (corindon) in water, which leads to the synthesis of nanoparticles of γ-Al2O3. The AlO blue-green emission and the Al(I) (2)P(0)-(2)S doublet emission provide the electron density, the density ratio between the Al atoms and AlO molecules, and the rotational and vibrational temperatures of the AlO molecules. These diagnostic considerations are discussed in the framework of theoretical studies from the literature (density functional theory). We have found that starting from a hot atomized gas, the nucleation cannot occur in the first microseconds. We also raise the question of the influence of water on the control of the stoichiometry.

We performed laser ablation of doped oxides, Y 2 O 3 :-Eu 3þ , Gd 2 O 3 :Eu 3þ , and Y 3 Al 5 O 12 :Ce 3þ (YAG:Ce), in an aqueous solution of 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA). Nanoparticles are produced and characterized using electron microscopy and luminescence spectroscopy. We show that the polyether chain ensures the stabilization of the objects formed in aqueous medium while the complexing group limits their size and sharpens the size distribution. The nanoparticles produced from the sesquioxide targets are in a "cubic disordered" phase as expected for very small particles. The ablation of the YAG target leads to a majority of R-Al 2 O 3 and YAG nanoparticles and a minority of YAlO 3 nanoparticles. Infrared spectroscopy is used to characterize the nature of the complex formed between the ligand and the particle surface. We demonstrate that the coordination mode of the carboxylate (-COO -) group to metal ions of the nanoparticles' surface is the bridging bidentate mode.

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