Synthesis, structure and nonlinear optical properties of solution-processed Bi₂TeO₅ nanocrystals

Nonlinear optical (NLO) nanocrystals like bismuth tellurite (Bi₂TeO₅) have attracted increasing interest in the applications of nonlinear micro-photonic devices, bioimaging and holographic devices. These NLO applications require the development of facile synthesis methods to prepare NLO nanocrystals on a large scale. Here, a novel solution-based method using a mixed solvent is proposed to synthesize layered Bi₂TeO₅ nanocrystals with controllable sizes and shapes, such as nanobelts, cross-shaped and rectangular nanoplates. These solution-processed Bi₂TeO₅ nanocrystals can be easily formed in a mixed solvent of ethylene glycol and water when heated at the boiling temperature of 128–141 °C for only 3 hours. The successful formation of Bi₂TeO₅ nanocrystals is certified by transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The Bi₂TeO₅ nanocrystals are confirmed to be nonlinear optically active for second-harmonic generation (SHG), and their non-centrosymmetric and rotational symmetric structures are also identified by the SHG test. This facile solution-processed method paves an intriguing way for developing other NLO nanocrystals and nanophotonic devices.