UPCONVERSION IN beta-NaYF4: Yb3+, Tm3+: SYNTHESIS, EXPERIMENTS, AND MODELS

The scientific method has enabled us to understand some of the deepest questions about ourselves and the world that surrounds us. The application of this method to all natural phenomena—the scientific endeavor—is one of the most important collective undertakings in the history of our species. This PhD thesis is merely a tiny step forward in this enterprise that now unites millions of people worldwide. Out of all scientific knowledge, this thesis concentrates on materials science; that is, how to create materials, what properties they have and, very importantly, why. From all possible materials and behaviors, this work studies certain optical properties of the insulator ceramic b-NaYF4. Its color and photoluminescence change dramatically when this material is impurified with specific elements, the rare earths; the study of these changes is the main focus of this thesis. In order to understand those changes in the luminescence, a microscopic model has been developed. It considers the absorption, emission, and transfer of energy between ions in a sample of a given crystallographic lattice and dopant concentration. Experimental measurements on low doped samples provide most of the model’s parameters. The experimentally inaccessible internal energy transfer parameters can be fit to experimental data, and thus, the nature and strength of those processes can be discovered