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.

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Seven resin-coated fertilizers (RCF) (Osmocote 19–6–12, 18–6–12, 14–14–14, 13–13–13, and 19–6–12, and Polyon 19–6–12, 17–17–17, and 13.5–13.5–13.5) were applied to marketable potted Alstroemeria hybrid FL101 plants to determine their effects on postproduction flowering and growth. The nonfertilized control produced the greatest number of floral stems, total florets, and mean number of florets per stem, but these plants were extremely chlorotic and spindly, and had the lowest fresh weight and number of vegetative stems. In a subsequent experiment, plants were fertilized with low, medium, and high concentrations of either Osmocote 19–6–12 or Sierra HighN 24–4–8. Nonfertilized controls were again chlorotic and spindly, but produced as many florets as fertilized plants. Plants fertilized with Osmocote 19–6–12 had greater fresh weight and more vegetative stems, but fewer total florets than those fertilized with Sierra HighN 24–4–8. We concluded that potted Alstroemeria do not need fertilizer for continued flowering, and fertilization favors production of vegetative stems relative to flowering stems. However, application of RCF to marketable plants prevents chlorosis, increases fresh weight, and, if low to moderate rates of formulations with N–P ratios of at least 6:1 are applied, does not inhibit flowering.

An analysis of luminescence polarisation measurements has been performed to study the aggregation processes of Pb" impurities in ionic crystals. The experimental approach was carried out by means of optical measurements (degree of luminescence polarisation, absorption, and excitation and emission spectra) on samples with different impurity concentrations. The analysis of the experimental results was performed following the theoretical calculations performed by Corish et ai and Bannon et al. The theoretical and experimental picture obtained for these crystals explains the first aggregation steps of the ion-vacancy dipoles (in particular, the Suzuki phase formation) and allows us to assign absorption bands to some types of aggregate.

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