Transitions between energy levels, origins

Spectral emission lines originate from electronic transitions between energy levels of atoms or ions. The frequency of the photons emitted is related, by Planck s constant, to the energy difference between the upper and lower energy states, or... 

Isotopes with 1 = 0 have no hyperfine structure, but in transitions between energy levels in a mixture of I = 0 isotopes of the same element, a line structure may still be obtained. This effect is called the isotopic shift. It has two origins and a distinction is made between the mass effect and the volume effect. The mass effect can be divided up into the normal and the specific mass effects. The normal mass effect is due to the movement of the nucleus, which is due to the fact that it is not infinitely heavy. For hydrogenic systems it is possible to take this into account by using the reduced mass fi instead of m... 

Transitions between the valence and conduction bands in semiconductors. These are the origin of colour in semiconductor pigments and quantum dots. In addition to colour from bandgap transitions, introduction of dopants or impurities into semiconductors leads to localised energy levels on the dopant or impurity atoms/molecules (so-called colour centres) and transitions between these levels and those of the semiconductor conduction and valence bands become possible the colour in blue and yellow diamonds arises firom these types of transitions. 

Much of the radiation with which we are familiar in everyday life is of thermal origin, arising by definition from matter in thermal equilibrium. In an ideal atomic gas in thermal equilibrium, for example, the upward versus downward transitions of bound electrons between energy levels in individual atoms are in close balance due to the exchange of energy between particles via collisions and the absorption and emission of radiation. The velocities of particles in an ideal thermal gas follow the well-known Maxwellian distribution, and the collective continuous spectrum of the radiating particles is described by the familiar Planck black-body radiation curve with its characteristic temperature-dependent profile and maximum. 

A. Electronic (Ultraviolet and Visible) Absorption Spectra The electronic absorption spectra of heterocyclic molecules have their origins in the transitions of electrons between different molecular orbitals. In general, the more these orbitals are spread out in space, the closer together are their energy levels and the longer the wavelengths... 

The properties of 7-rays are indistinguishable from those of x-rays of the same wavelength, but they do differ in origin. A 7-ray is emitted by a nucleus upon the occurrence of a quantum transition between two energy levels of the nucleus. For our purposes, only the 7-rays originating in radioactive nuclei need be considered. 

Electron transitions can take place between the valence band and the conduction band, as well as between the energy bands and local levels depicted in Fig. 10. In the case of a semiconductor and not too low temperature, these transitions are of thermal origin. Because of them an electron may pass to the conduction band or to an acceptor level. A, or it may be removed from a donor level D. 

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