In this study, the optical properties of nanocrystalline europium doped yttria, Y2O3:Eu3+ were investigated in dependence on different caging hosts such as porous MCM-41, porous silica, and porous alumina with pore sizes ranging between 2.7 to 80 nm. These results were compared to nanopowders measured in air and aqueous solution whose particle sizes were 5 nm and 8 nm, respectively. All these results were compared to a commercial lamp phosphor powder with a grain size of about 5 μm. The structural properties of the samples were determined by x-ray diffraction and transmission electron microscopy. Investigated optical properties are the photoluminescence emission spectra, the excitation spectra, the lifetimes, and the quantum efficiencies. A heavy dependence of the charge transfer process on the surrounding will be reported and discussed.

Control over spatial positioning of CdSe quantum dots(QDs) is a very important criterion for device fabrication. These authors utilize the ordered array of pores provided by the mesoporous material MCM‐41 to achieve this. TEM of a single CdSe@MCM‐41 particle (see Figure) shows that the hexagonally ordered mesostructure of MCM‐41 is still intact after the growth of CdSe nanoparticles inside the mesopores.

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Model predictions for the dendrite growth velocity at low undercoolings are deviating significantly from experimental data obtained in electromagnetic levitation with a capacitance proximity sensor (CPS) [K. Eckler, D.M. Herlach, Mater. Sci. Eng. A 178 (1994) 159]. In addition to that, previous data sets obtained by different techniques are not in good agreement with each other. For instance, growth velocity data for nickel melts obtained with a high-speed camera system [D.M. Matson, in: Solidification 1998, TMS, Warrendale PA, 1998 show higher values at low undercoolings than data obtained with the CPS. Within this work new measurements of dendritic growth velocity in levitated undercooled nickel samples were performed as a function of undercooling DT to investigate this discrepancy. Solidification of the undercooled melt was detected at undercooling levels within the range of 30 KoDTo300 K. The new data reveal high accuracy and low scattering. These data are compared with two independent growth velocity data sets and discrepancies are discussed. For verification of the new CPS data dendrite growth velocity was also measured by using a high-speed camera where the morphology of the intersection of the solidification front with the sample surface was investigated. The new experimental data are analyzed within the model of dendrite growth obtained on the basis of Brener's theory [E. Brener, J. Crystal Growth 99 (1990) 165] and the model of dendrite growth with melt convection in a solidifying levitated drop, presently being developed. Special attention is paid to the effects of convection and small amounts of impurities on the growth dynamics at small undercoolings. r

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