deexcite

Deexcite is a verb that describes the process by which a system transitions from a higher-energy state to a lower-energy state, releasing energy in the process. In physics, de-excitation encompasses electronic, nuclear, molecular, and solid-state contexts, including atoms, ions, molecules, nuclei, and excitations in materials. The term covers spontaneous relaxation as well as stimulated transitions induced by external radiation or interactions.

Radiative de-excitation releases energy as photons. In atomic and molecular systems, this appears as fluorescence or phosphorescence, depending on the spin and selection rules that govern the transition. In nuclear physics, de-excitation typically occurs through gamma-ray emission. The rate of radiative decay depends on the transition probability and can vary from very fast to relatively slow, producing short-lived or metastable states.

Nonradiative de-excitation dissipates energy without photon emission. Mechanisms include internal conversion, where energy is transferred to an orbital electron and ejected, and Auger processes, where energy is transferred to another bound electron, which is ejected or its energy redistributed. In solids and liquids, energy may be transferred to lattice vibrations (phonons), causing quenching of luminescence or relaxation through nonradiative channels.

Timescales for de-excitation span from picoseconds to milliseconds or longer, depending on the system and environment. Factors such as temperature, pressure, impurities, and surrounding media influence rates through collisional quenching, energy transfer, or changes in electronic or nuclear structure.

De-excitation underpins spectroscopy, photoluminescence, and laser operation, and is relevant to radiation safety and imaging. The term is often used broadly, with specific contexts distinguishing radiative, nonradiative, and stimulated de-excitation from excitation, the complementary process that populates higher-energy states.