Nanocrystals' optical properties promise global warming solution, efficient lighting, bio research apps

Researchers at the Lawrence Berkeley National Lab say their inexpensive, non-toxic nanocrystals could play a role in long-term storage of carbon dioxide—a potential means of tempering the effects of global warming. The nanocrystals, made from magnesium oxide, efficiently emit blue light when exposed to ultraviolet energy.

Current methods for generating such nanoparticles cause undesirable growth or fusing, or are time and cost intensive. "We've discovered a fundamentally new, unconventional mechanism for nicely controlling the size of these nanocrystals, and realized we had an intriguing and surprising candidate for optical applications," said Delia Milliron, facility director of the Inorganic Nanostructures Facility at Berkeley Lab's nanoscience research center, the Molecular Foundry. "This efficient, bright blue luminescence could be an inexpensive, attractive alternative in applications such as bio-imaging and solid-state lighting."

Unlike conventional incandescent or fluorescent bulbs, solid-state lighting makes use of light-emitting semiconductor materials--in general, red, green and blue emitting materials are combined to create white light. However, efficient blue light emitters are difficult to produce, suggesting these nanocrystals could be a candidate for lighting that consumes less energy and has a longer lifespan.

And the nanocrystals will be a subject of study in Berkeley Labs' Energy Frontier Research Center (EFRC) for Nanoscale Control of Geologic CO2, designed to establish the scientific foundations for the geological storage of carbon dioxide. Experts say carbon dioxide capture and storage will be vital to achieving significant cuts in greenhouse gas emissions, but the success of this technology hinges on sealing geochemical reservoirs deep below the earth's surface without allowing gases or fluids to escape. If properly stored, the captured carbon dioxide pumped underground forms carbonate minerals with the surrounding rock by reacting with nanoparticles of magnesium oxide and other mineral oxides.

"These nanocrystals will serve as a test system for modeling the kinetics of dissolution and mineralization in a simulated fluid-rock reservoir, allowing us to probe a key pathway in carbon dioxide sequestration," said Jeff Urban, a staff scientist in the Inorganic Nanostructures Facility at the Molecular Foundry who is also a member of the EFRC research team. "The geological minerals that fix magnesium into a stable carbonate are compositionally complex, but our nanocrystals will provide a simple model to mimic this intricate process."

Hoi Ri Moon, a post-doctoral researcher at the Foundry working with Milliron and Urban, noted her team's direct synthesis method could also be helpful for already-established purposes. "As a user facility that provides support to nanoscience researchers around the world, we would like to pursue studies with other scientists who could use our nanocrystals as 'feedstock' for catalysis, another application for which magnesium oxide thin films are commonly used," said Moon.

For more information see the paper, "Size-controlled synthesis and optical properties of monodisperse colloidal magnesium oxide nanocrystals," at Angewandte Chemie International Edition online.