Collaborative Research: Designer Glass Ceramics

Northwestern University, Evanston IL

Investigators

Abstract

Non-technical Description: This research creates special coatings for solar cells that increase the amount of the sun's energy that the cells can use, making them more efficient. The coatings also help reduce heating of the solar cells, which wastes energy. These coatings can be used with currently-available solar cell materials, enabling more attractive viability as a commercial product. The coatings may also be applied to light emitting diodes, helping control the color of light over a wide temperature range. Although not the focus of this investigation, the coatings have additional applications in medical X-ray imaging, non-destructive evaluation and homeland security. These research efforts are integrated with educational activities exposing graduate students to real world problems of energy saving as well as the full academic experience of information dissemination in the form of writing papers and presenting research, travel, grant writing and teaching. As part of the outreach activities, a summer internship is available for high school and undergraduate students, which gives a small number of students, each year, the opportunity to learn more about scientific research, perform experiments, give presentations, and participate in many other aspects of a scientific career. Technical Description: The aim of this activity is to develop novel 'designer' glass ceramics based on a modified fluorozirconate glass composition, and to explore their luminescence behavior. The ultimate goal is to gain insights leading to optimization of these designer nanocomposites for applications as wavelength shifters pertaining to up- and down-converters in solar cells and light emitting diodes. Pulsed laser deposition is used to synthesize layered nanocomposite materials so that very fine control of the distribution of the optically-active dopant and the nanocrystalline structure responsible for the optical behavior is achieved, leading to the development of a glass ceramic with enhanced light output. Systematic studies of optical behavior, as a function of parameters such as the designed distribution of the optically-active component layers within the glass matrix and the relative concentrations of optical dopants and nanocrystals, enable an understanding of how energy transfer between the luminescent dopant atoms and the nanocrystals (and thus the optical efficiency) can be controlled. The combination of in situ¬ transmission electron microscopy, ellipsometry and X-ray diffraction enables the structure-property relationships to be visualized and linked together. For example, critical control over optimum dopant position can be achieved by studying the diffusion paths of the dopants during in situ heating.