When Halides Come to Lithium Niobate Nanopowders Purity and Morphology Assistance

Highly Stable Colloidal Lithium Niobate Nanocrystals with Strong Violet and Blue Emission

High-quality LiNbO₃ colloidal nanocrystals were synthesized by the sol-gel technique. Morphological, structural, and optical spectroscopy methods were used to characterize LiNbO₃ colloidal nanocrystals. To investigate the optical properties, UV-visible absorption spectroscopy was used, which showed that the absorption peak was around 250 nm. Zeta potential was used to determine the stability of colloidal LN nanoparticles. Selected area electron diffraction patterns and X-ray diffraction patterns indicated that the dried LiNbO₃ sol formed in the rhombohedral crystal system. Field-emission scanning electron microscopy and transmission electron microscopy were used to study the morphological properties, which showed that the average diameter of colloidal nanocrystals is about 23 nm. Finally, two emission peaks were observed at 420 (violet) and 485 nm (blue) wavelengths in the photoluminescence (PL) spectrum. Also, using the PL measurements, the quantum yield for colloidal LiNbO₃ was calculated to be 87% at an excitation wavelength of 250 nm. Experimental results have shown that highly stable LiNbO₃ colloidal nanocrystals were synthesized that have enough potential for quantum photonics applications such as waveguides. The highly stable colloidal form of LiNbO₃ nanocrystals has not been synthesized before, and the mentioned optical properties are reported for the first time.

One-pot synthesis of sub-10 nm LiNbO3 nanocrystals exhibiting a tunable optical second harmonic response

Nanophotonics, dealing with the properties of light interacting with nanometer scale materials and structures, has emerged as a sought after platform for sensing and imaging applications, and is impacting fields that include advanced information technology, signal processing circuits, and cryptography. Lithium niobate (LiNbO₃) is a unique photonic material, often referred to as the "silicon of photonics" due to its excellent optical properties. In this article, we introduce a solution-phase method to prepare single-crystalline LiNbO₃ nanoparticles with average diameters of 7 nm. This one-pot approach forms well-dispersed LiNbO₃ nanocrystals without additional organic additives (e.g., surfactants) to control growth and aggregation of the nanoparticles. Formation of these LiNbO₃ nanocrystals proceeds through a non-aqueous sol-gel reaction, in which lithium hydroxide and niobium hydroxide species were generated in situ. The reaction proceeded through both a condensation and crystallization of these reactants to form the solid nanoparticles. These nanocrystals of LiNbO₃ were active for optical second harmonic generation (SHG) with a tunable response from 400 to 500 nm. These nanoparticles could enable further development of non-linear optical techniques such as SHG microscopy for bioimaging, which requires the dimensions of nanoparticles to be well below 100 nm.