Atomic Electron Transitions:
Atomic electron transition is a change of an electron from one quantum state to another within an atom or artificial atom. It appears discontinuous as the electron “jumps” from one energy level to another in a few nanoseconds or less. It is also known as atomic transition, quantum jump, or quantum leap.
Electron transitions cause the emission or absorption of electromagnetic radiation in the form of quantized units called photons. Their statistics are Poissonian, and the damping of statistic values of time between jumps is exponential on average. The damping time constant (which ranges from nanoseconds to a few seconds) relates to the natural, pressure, and field broadening of spectral lines. The farther the electron jumps, the shorter the wavelength of the photon emitted, meaning they emit different colors based on how far they jump.
The prediction and doubt was present in the 1980s.Nevertheless it was shown experimentally, that the fluorescence rate of a single atom can not be calculated by Maxwell-Bloch equations.
Although changes of quantum state occur on the submicroscopic level, in popular discourse, the term “quantum leap” refers to a large increase.
Molecular Electronic Transitions:
Molecular electronic transitions take place when electrons in a molecule are excited from one energy level to a higher energy level. The energy change associated with this transition provides information on the structure of a molecule and determines many molecular properties such as color. The relationship between the energy involved in the electronic transition and the frequency of radiation is given by Planck’s relation.