Shape-Controlled Synthesis And Self-Assembly Of Lanthanide Orthovanadate Nanocrystals

Lanthanide orthovanadates are currently attracting broad attentions due to their prospective utility in many fields, such as catalysts, polarizers, laser host materials and phosphors. Developing shape-controlled synthetic and self-assembly routes of lanthanide orthovanadate nanomaterials, investigating the influences of reaction parameters on the morphologies and phases of nanocrystals, and exploring the formation mechanisms and the relationship among the crystal structure, morphology and properties of nanomaterials have great significance. Self-assembly of nanocrystals provides fundamental scientific opportunities for investigating the size and dimensionality influences with respect to their collective optical, electronic properties and potential applications in nanodevices. In this dissertation, cerium orthovanadate (CeVO4) nanocrystals with various shapes and sizes have been prepared in hydrothermal synthesis. Careful investigations on the influences of reaction parameters on the morphologies of nanocrystals were carried out. The synthesis and self-assembly approach is developed to fabricate other rare earth vanadate nanocrystals. The fluorescence of the arrays was also investigated. The details are summarized as follows:Cerium orthovanadate nanocrystals with various shapes and sizes have been prepared in hydrothermal synthesis, including nanoparticles, nanorods, nanorod arrays, nanosheaves and double-head broccoli nanocrystals. The influences of complexing agents, concentration, pH value, reaction time and temperature on the morphologies of nanocrystals were investigated.A synthesis and self-assembly approach to the two- or three-dimensional uniform CeVO4 nanorod arrays in aqueous media is developed. SEM, TEM and HRTEM were used to further investigate the crystal structure of the smectic superlattice of CeVO4 nanorods. The average diameter and length of the nanorods are estimated to be about 7-10 nm and 70-100 nm respectively. The formation mechanism was also investigated. Key to the controlled synthesis is the use of ethylenediaminetetraacetic acid (EDTA) to mediate the nanocrystal growth in aqueous media instead of organic solutions used previously.For a further step, the hydrothermal synthesis of CeVO4 nanorod arrays were stretched to the other rare earth orthovanadate (LnVO4, Ln= La, Pr, Nd, Sm, Gd and Eu). The fluorescence of Ln3+ doped LnVO4 nanorod arrays was investigated.