Excited states refer to the higher-energy states that atoms, molecules, or nuclei can occupy when they absorb energy from an external source, such as light or electricity. These states are temporary and unstable, and the particles eventually return to their lower-energy ground state by emitting the excess energy in the form of photons. Excited states play a crucial role in a wide range of scientific disciplines, including chemistry, physics, and materials science, as they provide valuable information about the electronic structure, reactivity, and properties of matter. Researchers study excited states using various experimental techniques, such as spectroscopy, as well as theoretical models to better understand their behavior and potential applications.