Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Science




Liu, Lijia


Cr doped ZnGa2O4 (Cr-ZGO) has shown potential in the field of bioimaging. To achieve the nano-size suiting for bioimaging, Cr-ZGO is normally synthesized using a hydrothermal method. There are few studies on how the hydrothermal conditions influence the structure and optical properties of the Cr-ZGO. The first two parts of this thesis study how different hydrothermal temperatures and pH environments will affect the optical properties of Cr-ZGO by photoluminescence spectroscopy. By combining the electronic structure information extracted from X-ray absorption near-edge structures (XANES) and extended X-ray absorption fine structure (EXAFS), a relationship among hydrothermal conditions, optical properties and electronic structure is built. The last part studies how the surface functionalization will affect the optical properties of Cr-ZGO synthesized under different hydrothermal conditions. It turns out oxygen vacancies around Zn will improve the emission intensity, Cr-ZGO synthesized at a low pH environment shows the strongest emission after functionalization.

Summary for Lay Audience

Cr doped ZnGa2O4 (Cr-ZGO) is a new generation of persistent luminescent nanomaterials, which exhibit long-lasting luminescence for minutes or even hours after the excitation sources are removed. Cr-ZGO can emit light around 700 nm, which can be detected through tissue. Due to its desirable size and outstanding optical properties, persistent luminescent nanomaterials have shown potential in the field of visualizing biological activity. However, the optical properties can be affected by the crystal structure, and different parameters during the experiment can lead to different crystal structures. There will be some defects formed during the formation of the crystal. This means the crystal does not grow as the ideal structure. However, those defects are important for the persistent luminescent because they can store the electrons and release them slowly. During this process, the energy is released in the form of light. Therefore, this project studies how temperatures and pH environments, which are two important parameters during the synthesis of Cr-ZGO, will affect the crystal structures and the optical performance of different structures. To study the optical performance, the Cr-ZGO samples synthesized under different temperatures and pH environments are excited by different wavelengths. Then synchrotron-based techniques are used to determine the local chemical structure of different Cr-ZGO samples. It turns out that Cr-ZGO samples synthesized under 170 ℃ and pH=7 show fewer oxygens surrounding Zn in Cr-ZGO, which will increase the emission intensity. The last part talks about when the surface of Cr-ZGO samples synthesized under different conditions is functionalized by certain function groups, how the optical performance is affected. It turns out samples synthesized under low pH show the strongest light emission after functionalization.