Clays: A family of finely crystalline materials, composed primarily of silicates, with layered crystal structures. Clays may be refined from geological materials or may be synthetic.

Crystal grain boundary: Crystalline materials are composed of atoms arranged in an orderly way, in precise relationships to one another. A grain boundary is a narrow region of transition for one ordered area to another of different crystallographic orientation - an interface between one crystal grain and another.

Feature size: Refers to the particle size or crystalline grain size.

Ion exchange: A chemical reaction involving the exchange of hydrated ions in a solid for similarly charged but different element ions in solution.

Nanomaterials: Nanoscale materials; materials with structural features (particle size or grain size, for example) of at least one dimension in the range 1-100 nm.

Nanometer: One-billionth of a meter (10-9 meter).

Nanotechnology: Processes, systems, and materials that involve at least one dimension in the nano (sub-micron) range. The term has been used in various ways by different authors.

Photoluminescence: Emission of light from a molecule or atom that has absorbed electromagnetic energy. Examples include fluorescence and phosphorescence.

Polyimide: A family of polymers involving carbon and nitrogen bonds, known for good thermal stability.

Polymeric materials: Materials composed of large molecules, generally based on carbon, that have been formed from the chemical bonding of smaller units (monomers). Commonly known as plastics.

Polymerization: A chemical reaction resulting in the bonding together of small molecular units (monomers) to form a much larger molecule (polymer). There are many different routes, or reaction mechanisms, for polymerization.