Elektronenübergänge an farbzentren

The electronic properties of the F' center in KCl were calculated by a variational procedure using a Hamiltonian which approximates the effects of polarization and correlation. The trial functions were orthogonalized to nearest and next nearest neighbor core functions. Values of -1.05 eV for the F' maximum absorption and -0.49 eV for the thermal dissociation energy were obtained. By approximating the continuum states of the ionized F' center by eigenstates of an appropriately chosen spherical square well, the shape of the F' band itself was also calculated and the results compared with Liitys experimental data of F' absorption in KCI. Fair agreement was obtained. Die elektronischen Eigenschaften des F'-Zentrums in KCl wurden mittels einer Variationsmethode berechnet und dabei ein Hamilton-Operator verwendet, der Polarisation und Korrelation naherungsweise berucksichtigt. Die Variationsfunktionen wurden zu denRumpffunktionen der nachsten und iibernachsten Nachbarn orthogonalisiert. Piir die Lage des F'-Absorptionsmaximums ergab sich -1,05 eV und fur die thermische Ionisationsenergie -0,49 eV. Durch Annaherung der Kontinuumszustiinde des ionisierten F'-Zentrums durch Eigenzustande eines entsprechend gewahlten Topf-Potentials wurde auch die Form der F'-Bande berechnet. Ein Vergleich mit Liitys experimentellen Daten der F'-Absorption in KCI ergibt zufriedenstellende Ubereinstimmung.

Section: Introductioncontrasting

confidence: 61%

A Calculation of the Electronic Properties of the F′ Center in KCl

Strozier

Dick

1969

“…Furthermore, it has comnionly been assumed that the Fig. 7 shows that the quantum efficiency of the F-center emission is largely quenched between 100 and 180 K, as in crystals without M centers [16]. By contrast, the M-center emission is mostly constant between 77 and 180 K and decreases slightly a t still higher temperatures.…”

Section: Optical Properties Of the M Centermentioning

confidence: 97%

M‐Center singlet to triplet excitation in KCl

Schneider

Keller

1973

M centers are transformed to a triplet state either through the capture of an electron by an M+ center or through the optical bleaching of an M center. Using a technique similar to one previously developed by Schneider, Keller, and Klick, it is found that about four times as many triplets are produced through the M' mechanism than through the M'. I n these experiments, bleaching is produced with intense infrared excitation of short duration absorbed in the F' or M' bands for crystals which contain either M+ or M' centers. Evidence is also presented which indicates that the M+ mechanism might be predominant at low temperatures for continuous excitation in the F-spectral region. M-Zentren konnen entweder durch das Einfangen eines Elektrons von einem M+-Zen

“…We observed, however, that by the UV irradiation of the X-rayed crystal (which makes the M center ionization and bleaches out the VK and H centers) this thermo-luminescence becomes strongly suppressed and even completely quenched. Independent of this strength of the luminescence, we find the same amount of the electronic process (18).…”

Section: Bleaching Lcinetics 01 Rl Centers In Cqjstals X-raued At Lhetmentioning

confidence: 82%

“…However, following an idea introduced by Luty [18] such a capture process should be possible only for "non-correlated" Frenkel pairs, as for a correlated Frenkel pair the Coulomb field from the close lying interstitial should prevent the capture process through the excited F state by electrical field ionization. The first process leads to the same products as the reaction of the electron with the charged Frenkel pairs (equation (14))) namely ClGt and F centers.…”

Section: Formatiou Kinetics Of Fi Centers X-irradiated At Lhetmentioning

confidence: 99%

The F Center in KCl Crystals Part I: Formation and Bleaching Kinetics

Aegerter

Lüty

1971

A quantitative analysis of the higher transitions of the M center in the UV up to 5.0 eV in KC1 crystals with high [MI : [F] ratio and unaligned and aligned M centers shows several new excitations ("LM bands"). Assuming that the LM excitation leads to conductive states, a simple electron kinetic model shows that UV irradiation of the F + M center system produces ionized F and M centers (a and Fi) while competing capture processes partially destroyed them or form F and M centers. The F; center production spectrum should closely follow the absorption ratio of LM:LF while the bleaching spectrum should follow the F' and M spectrum. Experimental confirmation of this model is presented. By X-raying the