Improving the photoluminescence of CeO2 nanoparticles via creating oxygen vacancies in the crystal lattice

Abstract

Cerium oxide (CeO2) is a type of crystal semiconductor that's been getting a lot of attention lately because of its optical features, notably photoluminescence (PL). CeO2 nanoparticles can emit strong blue PL bands upon excitation by UV light (λ = 325), therefore, it can be utilized as a phosphor. Therefore, this study aims to enhance the utilization of cerium oxide as a phosphor in a broad range of industrial applications, by achieving multiple emissions in visible regions to facilitate its use in minimized costs in the various applications. In the context of the present study, an attempt to improve the usually emitted blue PL spectra of CeO2 was performed through CeO2 nanoparticles were subjected to thermal reduction in hydrogen environment at elevated temperatures (200–1000 °C). The obtained reduced samples were analyzed by using a variety characterization methods, including XRD, UV-Vis, SEM, XPS and HR-TEM. Characterization data showed that several oxygen vacancies are formed in the CeO2 lattice. The PL of the reduced CeO2 was investigated under different excitation wavelengths in the ultra-violet region (325, 345, 369, and 390 nm). It was found that the photoluminescence spectra of the original CeO2 sample either shifted or disappeared after thermal reduction. More importantly, new PL spectra in the wavelength range of 540 and 560 nm (greenish yellow) were observed. The intensity of these spectra was found to be increased with increasing the reduction temperature. The obtained results confirmed the possibility of obtaining different emitting PL spectra with several colors upon UV excitation compared to bare CeO2 nanoparticles. Therefore, reduced ceria can be used as a multi-color phosphor in several applications such as banknote watermarks.