There are several factors which conspire to limit the efficiency of solar cells. One of these is the fact that a solar cell is unable to absorb photons of energy less than the band gap of the semiconductor from which it is made; in the case of some high-band gap materials such as amorphous silicon – the model system used in this study – this can mean that as much as 50% of the solar spectrum is unusable. Upconversion phosphors – materials which can, by way of two or more successive photon absorptions, convert low energy (typically near infrared) light into high energy (typically visible) light – offer a potential solution to this problem as they can be used to convert light, which would otherwise be useless to the cell, into light which can be used for power generation. In this thesis we work towards the application of NaYF4-based upconverters to enhanced efficiency amorphous silicon (a-Si) photovoltaic power generation. We begin by synthesizing these upconverters at a range of temperatures and studying the crystallographic and spectroscopic properties of the resulting materials, elucidating heretofore undocumented trends in their luminescence and crystallography, including the effect of synthesis temperature on upconversion intensity, crystallite size, and lattice parameter. We also investigate the emission quantum yield of these materials, beginning with an in depth discussion and investigation of two methods for recording absolute quantum yields. We demonstrate that the quantum yields of the materials may vary by a factor of over 100, depending on the synthesis conditions. After we have fully characterized these properties we turn our attention to the application of these materials to amorphous silicon solar cells, for which we provide a proof of concept by demonstrating the effect of upconversion luminescence on the photoconductance of an a-Si film. We conclude by developing a roadmap for future improvements in the field.

Rare earth ferrosilicon is a versatile alloy mainly used to control the detrimental effects of sulfur in steel and to modify graphite structures in cast iron. The aim of this study was to optimize the experimental conditions for the production of rare earth ferrosilicon alloy by using a preconcentrate prepared from a bastnasite type of ore present in the Beylikahir-EskiSehir region of Turkey. After unsuccessful initial tests realized with this preconcentrate, however, two batches of rich-rare earth oxide concentrates with different compositions, that were supplied from the Turkish glass producer SiSecam A.S. were utilized in order to investigate the effects of several variables like temperature, duration, amount of reducing agents etc. on the recovery of rare earth metals and the alloy compositions. The findings of these tests were then tested again on the bastnasite preconcentrate. There was no difficulty in obtaining rare earth ferrosilicon alloys containing 35-55 wt % rare earths, 25-40 wt % silicon and 5-25 wt % iron, with about 80 % rare earth metal recovery in the tests made with rich rare earth oxide concentrates, while alloys containing up to 44 wt % rare earths, with 48 % rare earth metal recovery could be produced with the bastnasite preconcentrate.

Thesis (Ph. D.)--University of Adelaide, 1987. / Includes bibliographical references (leaves 132-147).

Thesis (Ph.D.)--University of Western Australia, 2006.

Thesis (M.Sc.)--University of Western Australia, 2008.

Thesis (Ph.D) -- Australian National University, 2005.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Mark A Riley, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Sept. 21, 2004). Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 70-74).

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 134-138). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references (leaves 134-138). Also available on the Internet.