Excitaties

Excitaties refer to processes in which a system gains energy and moves from a lower to a higher energy state. The term is used across physics, chemistry and related fields to describe excitations of electrons, molecular vibrations, spins or lattice modes. In atoms and simple molecules, an electronic excitation means promotion of an electron to a higher orbital, typically induced by absorption of light in the ultraviolet, visible or near-infrared and studied by UV–Vis spectroscopy. Molecules may also undergo vibrational or rotational excitations, excited by infrared or microwave photons and probed by infrared spectroscopy or Raman scattering. In solids, excitations include electronic transitions across a band gap, lattice vibrations (phonons), spin excitations (magnons), and bound electron–hole pairs called excitons.

Excitation can arise from photon absorption, thermal energy, chemical reactions or collisions. After excitation, the system often returns to a lower energy state via de-excitation, which can be radiative (emission of photons: fluorescence, phosphorescence) or non-radiative (internal conversion, vibrational relaxation, intersystem crossing).

Spectroscopic techniques capture excitations: absorption spectra reveal electronic and vibrational transitions; emission spectra reveal excited-state lifetimes and pathways; time-resolved methods quantify de-excitation dynamics. In biology and materials science, excitations underlie processes from photosynthesis to photovoltaics. In neuroscience, excitation denotes processes that raise neuronal membrane potential toward the firing threshold, triggering action potentials.