2eV

2 eV (two electron-volts) is a unit of energy commonly used in atomic, molecular, and solid-state physics. One electron volt equals exactly 1.602176634×10^-19 joule, so 2 eV equals 3.204353268×10^-19 J.

In photon terminology, a photon with energy 2 eV has a wavelength near 620 nanometers, since E = hc/λ and λ(nm) ≈ 1240/E(eV). Thus 2 eV photons lie in the visible red portion of the spectrum.

In materials science and electronics, energies expressed in eV describe band gaps, defect states, and carrier energies. A semiconductor with a band gap around 2 eV responds to red light; photons with energy above a material’s gap contribute to absorption and photocurrent. In spectroscopy, transitions in atoms and molecules are commonly quoted in eV.

Examples and notes: the He-Ne laser emits photons of about 1.96 eV (632.8 nm), which is close to 2 eV. Some photoemission experiments use photons near 2 eV to probe materials with relatively low work functions, while many common semiconductors have band gaps either above or below this energy, situating 2 eV photons near the boundary between visible and near-infrared regions.