Lanthanide and transition metal oxides are widely used in various applications such phosphors, lasers, magnets, and catalysts, and have formed an important platform for biomedical research and clinical medicine. The synthesis of highly uniform nanomaterials with controlled size, shape, and compositions is paramount to precisely understanding their physical properties and to arrange them into highly ordered arrays to design functional metamaterials. Herein, I describe novel chemistry to synthesize highly uniform lanthanide and transition metal oxide nanocrystals. The size, shape, and compositions of lanthanide-based nanocrystals are systematically controlled with the addition of alkali metal salts. The reaction mechanism is investigated to understand the nanocrystal growth and characterized by X-ray measurements and microscopic analysis. The magnetic resonance relaxometry and the optical properties including phosphorescece, upconversion, and X-ray excited optical luminescence are investigated, which make these nanocrystals a promising platform for multimodal imaging in biomedical applications. The shape-controlled synthesis of isotopically labeled rare earth fluoride nanocrystals is also demonstrated, which is designed for in vitro and ex vivo radioisotopic detection, as well as non-invasive nuclear, optical radioluminescence, and magnetic resonance imaging. Using anisotropic nanocrystal building blocks, shape-directed liquid crystalline self-assembly is presented to understand how complex anisotropic superstructures can be designed with single and binary components in a predictable manner. Finally, transition metal oxides such as tungsten, oxide, titanium oxide, and vanadium oxide are synthesized using non-injection heating up method. In addition, I demonstrate that vanadium oxide nanocrystal can be utilized as the precursors to fabricate thermochromic VO2, which is an important building block for energy research, optics, and electronic devices.