Public defence in Photonics and Nanotechnology, M.Sc. José Atalaia Rosa
M.Sc. José Atalaia Rosa will defend the thesis "Red-emitting Phosphor Fabrication by Atomic Layer Deposition" on 29 April 2022 at 12:00 in Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering, in lecture hall AS2, Maarintie 8, Espoo, and online in Zoom.
Opponent: Prof. Ola Nilsen, University of Oslo, Norway
Custos: Prof. Harri Lipsanen, Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering
Thesis available for public display at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/
Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53
Optoelectronic devices have become an essential technology in modern life. They are the core element in lamps, solar cells, lasers and displays. This fact explains the increasing interest in novel optoelectronic materials that and can revolutionize the way we live, or simply make our lives more comfortable and safer. A way to continue with the same development pace may rely on exploring unconventional features of certain fabrication techniques.
Atomic layer deposition (ALD) is one of the most promising fabrication technologies with the potential to achieve the required characteristics for the development of novel optoelectronic materials. The excellent fabrication control at the atomic level allowed by ALD, provides the ideal conditions for the development of high-quality thin films. Furthermore, the atomic control capabilities of ALD have recently been employed in the creation of mixed-anionic compounds which may be the key for the next-generation optoelectronic materials.
This thesis explores the fabrication of mixed-anionic compounds by ALD, as a way to change the properties of well-known red-emitting phosphors. In this work, properties such as the emitted wavelength of phosphor are studied and tuned by changing the anionic environment that surrounds the luminescent centres of the material. Two red emitting phosphors were investigated: CaS:Eu and Y2O3−xSx:Eu. In CaS:Eu, the luminescent centre (Eu) was grown in a CaS matrix using either H2S to fabricate CaS:Eu or O3 to develop CaS:EuO. Depending on the chemical molecule used to grow Eu the red phosphor peak emission assumed different wavelengths. In the case of Y2O3−xSx:Eu, the Eu ions were grown by pulsing either O3 or H2S. The Y2O3−xSx:Eu thin film grown with Eu(thd)3/O3 sequence emitted a red/pink colour. Instead, the use of Eu(thd)3/H2S sequence led to a violet/blue emission. As shown, ALD can be used as a method to control anionic inclusion and manipulate the properties of inorganic phosphors. This effect can be useful in the development of optoelectronic components, such as electroluminescent (EL) devices.
Another red phosphor was grown by ALD with the objective to address the lack of efficient re-emitting EL devices. To this end Y2O3:Eu was fabricated at low temperature, optimized and used in a multi-layered EL device.
Overall, the results presented in this work support the idea that rare-earth materials grown by ALD have great potential in the advancement of optoelectronic applications.