Kerr effect of CN- molecules in KCl crystals

The low lying tunnelling and hindered rotational states of dilute (z systems of substitutional CNions in KCI are studied by Raman techniques. The tunnelling splitting of the ground state could be directly observed as a resolved side-band structure of the CNstretching vibration. The observed splitting is in quantitative agreement with the previously derived value for the tunnelling splitting, while the appearance of this splitting only in the TQ scattering geometry confirms definitely the (111) dipole model. Hindered rotational structure (in the 10 to 30 cm-l range), which is partially resolved, is detected, both in the low energy and stretching-side-band spectrum in E, and Tzg symmetry. The observed Raman data can be fitted to the Raman positions and intensities calculated by Beyeler, using the V, + V , Devonshire model parameters derived from high resolution IR work. Nous avons Btudih, par spectroscopie Raman, les Btats tunnel et de rotation genee de CN-diluB (z lo-,) en position substitutionnelle dans KCI. Les transitions Raman entre les Btats tunnel du multiplet fondamental peuvent 6tre observees comme une bande de combinaison de la vibration du CNb 2089 cm-l, en symetrie T2, seulement. Ceci confirme definitivement I'orientation (111) du dipole. La difference d'energie observee (z 2,4 cm-l) correspondant B ces transitions est conforme aux valeurs proposees anterieurement. De plus, une structure partiellement resohe, due aux transitions entre les differents &tats rotationnels genes du CN-, est observee, en symetrie E, et T2g, b la fois dans le spectre Raman basse 6nergie et comme bandes de combinaison de la vibration du CN-. Les spectres Raman observes sont compares, en position et intensite, aux prBdictions d'un modble de type Devonshire en V , + 8, calcule par Beyeler pour representer ses resultats I R haute r&olution.

Section: Discussionmentioning

confidence: 85%

Raman Scattering from Tunnelling and Hindered Rotational States of CN⁻ Molecules in KCl

Durand

Lüty

1977

“…If a dipole system of the described properties becomes fully aligned in a field, the macroscopic refractive index differences for light polarized 11 and 1 to the field wiU be according to ( 4 ) T a b l e 1…”

Section: Field Alignment Of Polarixability Tensors and Resulting Kerrmentioning

confidence: 99%

Electro‐birefringence from paraelectric defects in cubic crystals

Lüty

Diaz‐Gongora

1978

The electro-birefringence effects are discussed and produced in an (electro-optically inactive) cubio crystal by the presence of electric dipole defects which are alignable by electric fields. Based on the electronic polarizability tensor of the defects and their paraelectric alignment functions, expressions for the field-induced birefringence (Kerr or Pockels effect) can be derived for all interesting symmetries of dipoles, electric fields, and light-geometry, and their connectionsby Kramers-Kronig relationsto elect,ro-dichroism can be given. Various methods for electrobirefringence measurements with dc, ac, dc + ac, and birefringence-bias techniques producing linear, quadratic, and quartic E-dependence of the electro-optical effect are discussed. The derived behavior is illustrated by experimental examples selected from Kerr effect measurements on CNdefects in alkali halides.Die feldinduzierte Doppelbrechung in kubischen Kristallen mit elektrischen Dipol-Stdrstellen wird diskutiert. Quantitative Ausdriicke fur den Kerr-und Pockels-Effekt (basierend auf dem Polarisierbarkeitstensor und der paraelektrischen Ausrichtfunktion der SMrstellen) werden fiir alle interessierenden Dipol-, Feld-und Lichtgeometrien angegeben, mitsamt ihrer Kramers-Kronig-Beziehung zum feldinduzierten Dichroismus. Verschiedene MeBmethoden mit Gleichspannungs-, Wechselspannungs-, Gleich-und Wechselspannungs-nnd ,,Doppelbrechungs-Vorspannangs"-Technik, die lineare, quadratische und quartische Feldabhangigkeit erzeugen, werden diskutiert. Das abgeleitete Verhalten wird illustriert mit experimentellen Beispielen von Kerr-Effekt-Messungen an CN--Stdrstellen in Alkali-Halogeniden.

“…The ultraviolet absorption was still unknown. The Kerr effect of KC1: CN- [5] prevents any conclusion about strength and position of this absorption besides the assumption that it might be hidden under the fundamental absorption of the host crystal. On the other hand the equation of Hilsch and Pohl [13] suggests a CN-absorption on the long wavelength side of the fundaniental absorption a t least in alkali chlorides and fluorides, taking 2.82 eV as the electron affinity of CN [6].…”

Section: Introductionmentioning

confidence: 89%

Ultraviolet absorption and emission of CN⁻ centres in alkali halides

Heyden

Fischer

1975

The ultraviolet absorption of CN-centres is studied in NaCI, KCI, RbCI, and NaBr single crystals, as well as the ultraviolet luminescence of NaBr : CN-. At low temperatures several CN-absorption bands are resolved from the low energy tail of the ultraviolet host absorption. These bands refer to the generation of valence vibrations of the excited CNmolecule. The ultraviolet luminescence of NaBr : CN-consists of well separated nearly equidistant bands (AE N 0.26 eV) in the range between 213 and 374 nm. This structure is refered to valence vibrations of the ground state CN-. The valence vibrations are described by Morse potentials. The experimental data allow the determination of the potential parameters, especially of the bond dissociation energy and of the change of the internuclear distance due to the electronic transition.Es werden die ultraviolette Absorption von CN--Zentren in NaCl, KCI, RbCl und NaBr sowie die ultraviolette Lumineszenz von NaBr : CN-an Einkristallen untersucht. Bei tiefen Temperaturen findet man mehrere Absorptionsbanden des CN-an der langwelligen Flanke der ultravioletten Grundgitterabsorption. Diese Banden erklaren sich aus der Erzeugung von Valenzschwingungen des angeregten CN--Molekuls. Die ultraviolette Lumineszenz von NaBr: CN-besteht aus deutlich getrennten Banden (AE = 0,26 eV); sie erstreckt sich uber den Bereich von 213 bis 374 nm. Diese Struktur wird zuriickgefuhrt auf die Erzeugung von Valenzschwingungen des CN-im elektronischen Grundzustand. Die Valenzschwingungen werden durch Morse-Potentiale beschrieben. Die experimentellen Daten erlauben die Bestimmung der Potential-Parameter, insbesondere der Dissoziationsenergie und der durch den elektronischen Ubergang bedingten h d e r u n g des Kernabstandes.