Synthesis by Size Focusing of Lithium Tantalate Nanoparticles with a Tunable Second Harmonic Optical Activity

Abstract: Nonlinear optics at the nanoscale has emerged as a sought-after platform for sensing and imaging applications. The development of these materials is having an impact on fields that include advanced information technology, signal processing circuits, and cryptography. Lithium tantalate (LiTaO3) is an attractive nonlinear optical material due to its high optical damage threshold (e.g., tolerance to greater than 500 MW per cm^2 from a nanosecond pulsed laser) and broad range of ultraviolet-visible (UV-Vis) transparency relative to many other nonlinear optical materials. Despite many synthetic reports on metal oxides, very little is known about the preparation of uniform, crystalline LiTaO3 nanoparticles (NPs) of a pure phase, as well as details on their mechanism of nucleation and growth. In this article, we introduce a solution-phase method for the preparation of LiTaO3 NPs with tunable dimensions. This solution-phase process results in the formation of crystalline, uniform NPs of LiTaO3 of a pure phase when carried out at 220 C. This method can prepare crystalline LiTaO3 NPs without the need for further heat treatment or the use of an inert atmosphere. Results presented herein also provide insights into the growth mechanism of these NPs. The reaction included the processes of oriented attachment and Ostwald ripening. The results of our study also indicate that the growth of the LiTaO3 NPs was a result of a size focusing effect, which enables the ability to tune their diameters from 200 to 500 nm. The crystalline NPs were optically active towards second harmonic generation. These studies deepen our understanding of the methods by which NPs can be prepared from metal oxides. These studies specifically demonstrate the preparation of optically active LiTaO3 NPs of uniform and controllable dimensions that could be used in a broad range of fundamental studies and applications in nanophotonics.