Luminescent Center

luminescent center

[‚lü·mə′nes·ənt ′sen·tər]
(solid-state physics)
A point-lattice defect in a transparent crystal that exhibits luminescence.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Luminescent Center

 

a lattice imperfection that is responsible for the luminescence of a phosphor (seeLUMINESCENCE).

In crystal phosphors, luminescent centers may result from crystal defects—such as positive-and negative-ion vacancies or interstitial atoms and ions—or from activators, which are specially introduced atoms or ions. Luminescent centers that result from crystal defects are called host-crystal centers; those that result from activators are known as activator centers. A distinction is made between simple and complex luminescent centers. Simple luminescent centers are point defects or single activator atoms or ions; complex centers are pairs or clusters of defects or activator atoms, often atoms of different species.

In luminescent glasses, the luminescent centers are activator centers. The centers are produced during the manufacture of the glasses by adding an activator material to the batch.

The main characteristics of luminescent centers are their emission and absorption spectra. As a rule, the absorption spectrum lies in a spectral region where the crystal does not absorb light. Hence, luminescent centers are often color centers as well, although not all color centers are luminescent centers. On the other hand, if a luminescent center absorbs light in the same spectral region as does the crystal, the center will luminesce and, thus, would not be a color center.

The absorption and emission spectra of simple activator centers are related to the activator atoms. For example, when a phosphor is activated by ions of rare earth elements, the spectra of the luminescent centers turn out to be line spectra produced by quantum transitions in the inner electron shells of the ions. The effect of the lattice is manifested in the shifting and splitting of the spectral lines by the crystal field—for example, the Stark effect—and in the superposition of additional frequencies corresponding to lattice vibrations (seeSPECTRUM, CRYSTAL). When a phosphor is activated by atoms of elements whose spectra are produced by transitions in an outer electron shell, the lattice causes the spectral lines to be broadened into bands.

In a regular lattice, the activator ions usually replace the cations. However, under certain conditions of phosphor preparation, the activator ions also may be localized in planes within the crystal that contain defects or in the vicinity of some crystal defect, thus also constituting a luminescent center.

A single phosphor often contains two or more types of luminescent centers. The centers may interact with one another by exchanging electrons and holes or directly by means of excitation energy. The first type of interaction is called a recombination interaction; the second type is known as a resonance interaction.

REFERENCES

Levshin, V. L. Fotoliuminestsentsiia zhidkikh i tverdykh veshchestv. Moscow-Leningrad, 1951.
Feofilov, P. P. Poliarizovannaia liuminestsentsiia atomov, molekul i kristallov. Moscow, 1959.
Antonov-Romanovskii, V. V. Kinetika fotoliuminestsentsii kristallofosforov. Moscow, 1966.

Z. L. MORGENSHTERN

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
These results show that although the PLD target was obtained by pressing Nd[F.sub.3] and Lu[F.sub.3] powders together (undoped material), [Nd.sup.3+] acted as a dopant for Lu[F.sub.3] and a luminescent center in the thin film.
This result suggested that [Nd.sup.3+] ion acted as a luminescent center and doped Lu[F.sub.3] in the synthesized thin film although the target used during PLD was obtained by pressing Nd[F.sub.3] and Lu[F.sub.3] powders into a pellet.
The MD transition does not appreciably depend on the chemical surroundings of the luminescent center and its symmetry; however, the ED transition belongs to hypersensitive transitions.
Luminescence of [Eu.sup.3+] is especially useful to probe the local structure of luminescent centers in a host lattice because of its simple energy level structure, great sensitivity to ligand field, and similar lanthanide chemical properties to the other rare earth ions [31-33].
The emission does not create heat; thus, it is also called "cold light." This type of emission, which uses the electron transition between valence and conduction bands or the collision of high energy electrons with the activator inside a phosphor layer and the luminescent center to excite and emit energy, is different from an LED, which employs the recombination of the electron-hole pair near the p-n junction to emit light.
Because ZnO materials can concurrently possess visible and invisible light (UV) emission properties, after discounting the self-emitting UV, the visible light emission is considered to result from an internal thin film defect, which is caused by electrons colliding with the luminescent center under high voltages.
- Phosphor material technology that utilizes the high-density crystalline structure of SMS (Sr3MgSi2O8) phosphor to control the density of the luminescent center and thus prevent luminous saturation.
The europium is efficiently used as luminescent center in phosphors for various purposes.
Decay kinetics behavior depends also on the number of different luminescent centers [20, 27].
Yamamoto, "Photoluminescence of Si-rich Si[O.sub.2] films: Si clusters as luminescent centers," Japanese Journal of Applied Physics, vol.
Previously reported luminescent centers (Mn2+ and Fe3+) were observed and their UV-Visible peak positions vary with stoichiometric changes in the Na-K-Ca composition of the feldspars as expected.
When the incident light on the surface of LSC is absorbed by the luminescent centers and isotropically reemitted over all the angles, a fraction of light ([approximately equal to] 75% for PMMA) is internally reflected within the plate and guided towards the edges, where small photovoltaic (PV) cells can be placed to convert the concentrated light into electricity [5].