Non-Centrosymmetric Oxide (NCO) materials are known to exhibit (multi)-functional properties that allow a range of useful applications in our everyday life. These properties, like piezoelectricity that is for instance used in ultrasound medical imaging (echography), must be understood in terms of “structure-property” relationships. The concept of dipole moment will first be introduced together with the reverse piezoelectric effect. Controlling a sample position with a nm resolution, when a low-frequency electric field is applied, is today very easy to achieve and at the heart of the well-known scanning probe techniques. STM and AFM will thus be rapidly discussed together with a few famous examples, allowing to quickly decipher some differences between science and science fiction. At high-frequency, in the optical domain, non-linear optics will then be also presented in terms of dipole moments and oscillating charges.
After this broad and general introduction dedicated to bulk NCO materials, the presentation will concentrate more on their preparation at the nanoscale with a special focus on the solution-based routes. They are indeed more prone to result in nanocrystals with size- and shape-control and, more importantly, with a low degree of aggregation, a prerequisite when biomedical applications are then foreseen. Our deep understanding of the reaction pathways and formation mechanisms of LiNbO3 nanoparticles will first be addressed. The synthesis is based on the aqueous sol-gel route after a simple mixing and hydrolysis of the metal alkoxide precursors. I will also provide insights that this sol-gel route can be easily extended to the preparation of highly-doped LiNbO3 nanocrystals with optimal concentrations in lanthanide ions such as Er3+ and Yb3+.
Before concluding, possible applications and recent proof-of-concept studies based on these NCO nanocrystals will also be introduced. In particular, our collaborators have developed advanced functionalization strategies to finely tailor their surface-chemistry so that specific cell-targeting and multi-modal imaging with the attachment MRI probes have been evidenced. The non-linear emission from the NCO nanocrystal cores is also studied with the aim to explore the local and on-demand photo-release of therapeutic agents.
