Phosphorescence

of phosphorescing Wikipedia signature

under phosphorescence one understands the special characteristic of a material caused by so-called radiating deactivation, which continues to glow after lighting up with (visible or UV ) light in the dark. Alchemisten already observed this phenomenon in 17. Century.

Phosphorescence is a special formthe luminescence (cold shining). It differs from the similar phenomenon of fluorescence in it that fluorescence ends after the end of the irradiation rapidly (usually within millionths a second), thus no light (in the spectrum visible for humans) is further-emitted, against what it with the phosphorescenceto an afterglow comes, which can last from fractions of a second up to hours. Phosphorescing materials are called also luminophores.

Phosphorescence was designated after the chemical element phosphorus (light carrier). The cause of shining elementary white phosphorus is however the chemical conversion of the phosphorus alsoAtmospheric oxygen, why one speaks here of chemoluminescence. This is based on a chemical (usually irreversible) reaction and not like the phosphorescence on a physical effect. Phosphorescing materials can be made however also of phosphorus.

Since phosphorescing materials store the light apparently, they become „phosphors “ or „luminophores “ called.

explanation

phosphorescence is a procedure of quantum physics. If a phosphorescing material with light quanta (photons) is lit up, then these photons deliver their energy to the electrons of the material.

The electrons carry out now a quantum transition into a higher energy level.The molecule changes from a singlet condition into high suppl. tables a singlet condition. This becomes descriptive, if one represents it in a so-called Jablonski diagram. In this the individual energy and oscillation levels are represented, which accept the electrons, if they take up energy and/or. deliver.

Jablonski-Diagramm der Phosphoreszenz
Jablonski diagram of the phosphorescence

usualthe electron, which is anxious to return to its unangeregten condition can deliver its gained energy; this happens, as the lively molecule collides with other particles and so to other particles transfers parts of its energy. On the Jablonski diagram this is by dropping the electron inlow oscillation levels drawn in. The energy is delivered normally as warmth, one calls this procedure oscillation relaxation.

If the particles can deliver their won energy not completely to its environment, it is added that the electrons deliver their surplus energy in form of a photon, thus asRadiation (light in the broader sense). With the phosphorescence this procedure does not run off completely however in such a way, since the light emission would end otherwise as with fluorescence with the irradiation.

It comes to a usual period spent from approximately 10 -8 seconds to a further quantum transitionthe electrons into a metastable energy level. Here the spin of the electrons changes, whereby the molecule under change of the multiplicity of a singlet changes into a triplet condition; one calls this procedure intercombination (English: intersystem crossing). The period spent in this condition is longer around some;them amount to milliseconds up to hours.

In this triplet condition it comes likewise to the oscillation relaxation, however the molecule is imprisoned in this put on condition „“, since a delivery of the energy is not possible to the environment. The triplet condition cannot strictly speaking in oneSinglet condition to be transferred, since a Spinumkehr is not possible. But it comes here to an exception. Indeed again to a forbidden intercombination process, like already with transferring the singlet into the triplet condition. A weak radiation can be emitted by it. The energy is only gradually delivered,which the typical afterglow produces.

The phosphorescence is temperature-dependent, since both and the loss of energy is strengthened by oscillation relaxation the intercombination is accelerated, if one supplies the system heat energy (see RGT rule).

http://www2.uni-jena.de/chemie/institute/oc/weiss/phosphoreszenz.htm

phosphorescing materials

phosphorescing materials are usually crystals with onesmall admixture of a foreign matter, which disturbs the lattice structure of the crystal. One mostly uses sulfides of metals of the second group as well as zinc and mixes small quantities of Schwermetallsalzen with (z. B. Zinc sulfide with traces of Schwermetallsalzen)


applications

in the Philatelie

During the production of stamps for some decades phosphorescing material is mixed to the paper pulp. Sometimes the material is also only later stacked up. Thus the individual stamps shine, if they are illuminated with UV light (in the dark one) after. This is particularly important for the automatic postmark machines. Thusthe machine can easily recognize where the stamps which can be cancelled on the letter to stick and can so the postmarks on the correct place reduce. Postage unpaid letters or postcards can be likewise easily selected with this method.

From similar reasons the stamp paper sometimes also fluorescent becomeMaterials added.

Sonstige

Phosphoreszierende Materialien werden weiters für Leuchtzeiger bei Uhren, an Lichtschaltern oder bei manchen Aufklebern (Sicherheitsschilder, Deko-Artikel) verwendet.


 

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