Nanoparticle-based Materials. The vision of IRG-4 is to explore nanoparticle-based materials that are non-toxic, environmentally benign, abundant, stable and economically manufacturable, and to understand their fundamental optoelectronic properties for luminescent and photovoltaic (solar-to-electric energy conversion) applications. The IRG focuses on semiconductor nanoparticles including group IV materials (Si and Ge) and several metal-oxides, whose constituent elements are among the most abundant in the earth's crust and non-toxic. IRG researchers study the size-tunable optical properties of nanoparticles, novel low-cost nanoparticle assembly approaches, and novel photo-physical phenomena in nanoparticles and nanoparticle films.