PACS. 71. 35 -Excitons and related phenomena (inc. electron-hole drops). PACS. 73.20D -Electron states in low-dimensional structures (inc. quantum wells, super-PACS. 78.47 -Time-resolved optical spectroscopies and other ultrafast optical measurement lattices, layer structures and intercalation compounds).

The temperature dependence of the photoluminescence (PL) of GaAs/GaAlAs multiple quantum wells is investigated. Emissions related t o transitions between n = 1 , 2 , 3 electron and hole subbands are observed. Theoretical evaluation of the energy levels fits nicely the experimental data. The temperature dependence of peak position and photoluminescence intensity and the dependence of P L intensity on the power excitation show that there are three different temperature regions. At low temperatures (22 t o 40 K) the main emission is ascribed t o exciton recombination while at temperatures higher than 100 K it can be attributed t o free carrier recombination. In the intermediate temperature region the P L involves both, excitonic and free carrier recombination. Thermally activated non-radiative recombination processes strongly reduce the luminescence quantum efficiency.Es wird die Temperaturabhangigkeit der Photolumineszenz (PL) von GaAs/GaAlAs-Mehrfachquantenwells untersucht. Emissionen, die mit Ubergangen zwischen n = 1 , 2 , 3 Elektronen-und Locher-Subbander verknupft sind, werden beobachtet. Eine theoretische Entwicklung der Energieniveaus stimmt gut mit den experimentellen Werten uberein. Die Temperaturabhangigkeit der Lage des Maximums und Photolumineszenzintensitiit und die AbhLngigkeit der P1-Intensitat von der Anregung zeigt, daB drei verschiedene Temperaturbereiche existieren. Bei niedrigen Temperaturen (22 bis 40 K) wird die Hauptemission einer Exzitonenrekombination zugeschrieben, wahrend bei Temperaturen hoher als 100 K sie der Rekombination freier TrLger zugeordnet wird. I m mittleren Temperaturbereich schlieBt die P L sowohl Exzitonen-als auch freie Ladungstrager-Rekombination ein. Ein thermisch aktivierter, nichtstrahlender RekombinationsprozeB reduziert die Lumineszenzquantenausbeute.

In digital image capture, the camera signals produced by the D65 illuminant, once translated into tristimulus values of the CIE 1931 standard colorimetric observer (assuming the Maxwell‐Ives‐Luther criterion is satisfied), are considered good to produce accurate color rendering. An image obtained under any illuminant other than D65 does not appear realistic and the tristimulus values of the camera must be transformed into the corresponding ones produced by the D65 illuminant. This transformation must satisfy color constancy. In this work, the transformation is obtained by a color‐vision model based on the Optical Society of America‐Uniform Color Scales system [Color Res Appl 2005; 30: 31–41] and is represented by a matrix dependent on the adaptation illuminant. This matrix is obtained by minimizing the distance between the pairs of the uniform scale chromatic responses related to the tristimulus values of the 99 different color samples of the SG Gretag‐Macbeth ColorChecker measured under a pair of different illuminants, one of which is the D65. Then any picture captured under a given light source can be translated into the picture of the same scene under the D65 illuminant. Metameric reason allows only approximate solutions. The transformations from Daylight and Planckian illuminants to the D65 illuminant have a very regular dependence on the color temperature, that appears to be the typical parameter for the color conversion. © 2012 Wiley Periodicals, Inc. Col Res Appl, 38, 412–422, 2013

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.