Quinizarin as Organic Sensitizer in LnF3 Thin Films for Photon Upconversion

This thesis illuminates the opportunities for Quinizarin (Qz) as an organic sensitizer in LnF3 (Ln=Y, Nd, Tm, Yb) thin films for upconversion. Lanthanides show great promise as active materials for upconversion technologies, but struggle with very low absorption and thus, very low efficiency. We attempt to correct this by including a broad band absorber, in our case an organic dye. Atomic layer deposition (ALD) has been used to build the multilayered structures with control of the interatomic separations. The project has been divided into multiple parts, focusing first on Qz as sensitizer and its properties in solid state by ALD growth of Ln2Qz3. The ALD growth of LnF3 thin films was investigated and multilayered structures intended to show upconversion was made. Initial investigations of Qz show that as a dispersed molecule, its luminescence is heavily influenced by its environment, but indicates it could function as a sensitizer. When combined with Ln(thd)3 as a precursor in ALD growth, it shows exceptionally good growth with high growth rate, as well as high optical absorption. The growth and structure of LnF3 thin films using NH4F as fluorine source has been characterized using quartz crystal microbalance (QCM), with results indicating similar type of growth among all the tested lanthanides, apart for Nd, which proved more challenging. Uniform film with growth rates of around 0.6 Å/cycle were achieved, and NH4F has been proven a good fluorine source in LnF3 systems using Ln(thd)3. Qz has been successfully incorporated into these films with high absorption for high Qz-content, as characterized by using ultraviolet, visible and near infrared spectroscopy (UV-Vis). However, the films were not luminescent, as aimed for, proving that there is more work to be done to understand the quenching mechanisms involved. The upconversion structure itself has been investigated by growing and investigating multilayers of YbF3 with Nd3+ and Tm3+. Using cathodoluminescence (CL) both ions have been shown incorporated in the structure. The system shows different emission intensities depending on ion distance, with 0.8 nm being the most optimal for CL signal.