What is intervalence charge transfer?

Intervalence charge transfer refers to the phenomenon where electrons can be transferred between two different oxidation states of metal ions that are separated by a non-conductive atom or ion within a crystal lattice. This process requires that one atom can donate an electron to another, even if they are not directly adjacent, which is facilitated through the mediating atom.

In the context of colored gemstones, this mechanism allows certain materials to selectively absorb specific wavelengths of light, leading to the vivid colors characteristic of some stones. For example, in gemstones like tourmaline or certain types of spinel, the presence of metal ions in different oxidation states can result in a wide range of colors depending on the specific arrangement and interactions of these ions.

Intervening atoms play a crucial role, as they allow for the electron transfer to occur without the direct contact that one might typically expect. This unique arrangement helps explain why certain gemstones exhibit specific coloration under different lighting conditions or when viewed from different angles.

The other options describe unrelated concepts. The process of changing color with heat pertains to thermochromism, enhancing clarity refers to treatments such as cleaving or filling, and the movement of electrons in response to light addresses photoexcitation, but not specifically intervalence charge transfer.