Thesis supervisors: dr Yury Orlovskiy and Valter Kiisk,
Opponents: prof José García Solé (Universidad Autónoma de Madrid, Spain) and dr Valdek Mikli (Tallinn University of Technology).
The development of novel methods for cancer diagnostics is one of the major focus areas for modern medicine. Fluorescence deep tumor imaging may be an efficient non-invasive diagnostics technique. A number of materials suggested to be potential candidates for fluorescence imaging agents. Rare-earth doped nanoparticles are of great interest of this respect, as they are more biocompatible than traditional organic phosphors and quantum dots, photo- and thermally stable. However, the fluorescence properties of these materials need further improvement. The main problem to be overcome in this respect is fluorescence quenching, which competes with the emission process. In order to be able to suggest a way to reduce quenching, one needs to study its causes and origin. This work is devoted to the study of origin of the fluorescence quenching in the rare-earth doped nanoparticles. For this, a so-called energy transfer probing technique was developed. By means of this tool it has been shown that the main source of fluorescence quenching is a significant amount of water molecules and –OH groups, originating from the solvent and distributed in the volume of the nanoparticles, mainly in mesopores formed during the material crystallization.