International audienceOxide nanoparticles (NP) are currently drawing a lot of attention because of their diverse applications such as catalysis, drug delivery, sensing and as luminescent materials. Clearly, optimizing the synthesis of such oxide nanoparticles is of high importance. In particular, the manufacturing of crystalline oxide nanoparticles in aqueous solution at room-temperature is industrially very appealing. However, this requires a detailed understanding of all the different phases involved in their formation from the initial homogeneous solution to the final crystalline mineral phase. This complex process is loosely described by the classical nucleation theory, which relies upon a single step description of the formation of the primary centers ("seeds") by means of dynamic and stochastic association of the ions in solution. In this picture, the ions must overcome the free energy barrier before developing to a crystal of critical size which can grow to a mature crystal. However, there is evidence of the existence of non-classical intermediates like clusters, nanoscale amorphous precipitates, and other complex precursors in the liquid phase. The existence of a transient amorphous network with a two-level structuration was indeed confirmed by Fleury et al in the case of Eu:YVO4 nanoparticles using In situ X-ray scattering and steady-state fluorescence techniques
