Spectral and time decay analysis of photoluminescence excited in the A band region in KCl:Pb

Abstract

The A band spectral region in KCI: Pb is studied from the point of view of the optical absorption spectra, photoluminescence (emission and excitation) spectra, and the luminescence lifetime measurements in the temperature range 15 to 320 K. The sensitive ITC technique is exploited as a parallel tool to monitor and check the solution state of the impurity in order to rule out the additional and unwanted complications arising from the presence of aggregates. As a consequence only very dilute (4 to 6 ppm) and quenched samples are chosen to perform the detailed and systematic analysis of the photoluminescence spectra. The emission and excitation spectra do not depend significantly on the wavelength of the exciting and emitted light respectively, while their shape depends strongly on the temperature. The careful analysis of the emission spectrum, which looks asymmetric and apparently structureless, suggests that two Gaussians are contributing to it (main band and red aide band, with associated average phonons of 1.25 x and 1.6 x 10-2 eV, respectively) for T < 120 K, while a third weaker component seem to increase on the high energy side (violet side band) for T > 120 K. The luminescence time decay is complex exhibiting three distinct lifetimes: the length of two of them (tl = 30 andt; = 160 ns) is temperature independent, while the third one t3 is strongly temperature-dependent. The comparison between the intensity behaviour versus temperature both, of the time decay components and of the emission spectral components brings to a tentative attribution of tl t o the main band, z2 to the violet side band, and t3 to the red side band. A scheme for the excited state energy levels, from which the emission excited by A light takes place is discussed both, by taking into account the dynamical Jahn-Teller effect and the role of the neighbouring cation vacancy. gaussiennes ("main band" et "red side band") pour T < 120 K et qu'une troisihme composante parait crottre dans la part des hautes energies pour T > 120 K ("violet side band"). Le signal de decroissance de la luminescence est complexe et est compos6 de troi composantes avec differentes valeurs de la vie moyenne: deux valeurs de la vie moyenne (tl = 30 et t 2 = 160 ns) ne dependent pas de la temperature tandis que la troisihme, t3, depende fortement de la tempbrature. Aprbs une comparaison entre l'allure de l'intensith (en function de la temp6rature) des composantes de la vie moyenne et des composantes du spectre d'bmission on va attribuer tl 8, la "main band", r2 8, la "violet side band" et t3 8, la "red side band". On discute un schema des niveaux excitAs desquels il y a l'bmission excithe avec la lumibre A en considerant l'effect Jahn-Teller et le r6le de la lacune.

On the Energy Transfer in the Thermally Annealed KCl: Pb2+, Eu2+ System

“…The quenched KCl: Pb2+ system is characterized by three absorption bands, but we are interested in the so-called A absorption band (centred at 273 nm) which corresponds to the 'So -+ 3P, transition and produces an emission band peaking at 340 nm. The decay scheme of this band is rather complex [6]. However, at room temperature it consists of a unique time decay constant whose value is about 200 ns.…”

The Pb2+(Li) and Pb2+(Na) Centres in KCl Crystals

“…In the case of the Pb 2+ centre, only the A T emission band has been observed (see e.g. [3,9,10,19]). Some investigators, however, have observed another emission band which has been believed to be attributable to the A X emission band, besides the A T emission band [11 to 14].…”

Energy Transfer in the Thermally Annealed KCI: Pb2+, Mn2+ System

“…The quenched KC1:Pb2+ system is charac- terized by three absorption bands but we are interested in the so-called A absorption band (centred at 273 nm) which corresponds to the 'So -+ 3P, transition and produces an emission band peaking at 340 nm. The decay scheme of this band is rather complex [5], however at room temperature it consists of a unique time decay constant whose value is about 200 ns.…”