Cathodoluminescence and electron microscopy of red quantum dots used for display applications

Cathodoluminescent imaging of the visible light emitted from quantum dots is reported. The shape and uniformity of individual particles is observed in the STEM electron image and the image of the particles created from their visible light collected simultaneously is shown. Visible light images of the 13nm sized particles are reported for clusters of particles. Emission spectra collected from a small clusters of QDs are also reported

Cathodoluminescence studies of phosphors in a scanning electron microscope

Cathodoluminescence studies are reported of phosphors in a field emission scanning electron microscope (FESEM). A number of phosphor materials have been studied and exhibited a pronounced comet-like structure at high scan rates, because the particle continued to emit light after the beam had moved onto subsequent pixels. Image analysis has been used to study the loss of brightness along the tail and hence to determine the decay time of the materials. This technique provides a simple and convenient way to study the decay times of individual particles

Generalized Stirling Permutations and Forests: Higher-Order Eulerian and Ward Numbers

We define a new family of generalized Stirling permutations that can be interpreted in terms of ordered trees and forests. We prove that the number of generalized Stirling permutations with a fixed number of ascents is given by a natural three-parameter generalization of the well-known Eulerian numbers. We give the generating function for this new class of numbers and, in the simplest cases, we find closed formulas for them and the corresponding row polynomials. By using a non-trivial involution our generalized Eulerian numbers can be mapped onto a family of generalized Ward numbers, forming a Riordan inverse pair, for which we also provide a combinatorial interpretation.We are indebted to Alan Sokal for his participation in the early stages of this work, his encouragement, and useful suggestions later on. We also thank Jesper Jacobsen, Anna de Mier, Neil Sloane, and Mike Spivey for correspondence, and David Callan for pointing out some interesting references to us. Last but not least, we thank Bojan Mohar for valuable criticisms and suggestions

Bivariate generating functions for a class of linear recurrences: General structure

We consider Problem 6.94 posed in the book Concrete Mathematics by Graham, Knuth, and Patashnik, and solve it by using bivariate exponential generating functions. The family of recurrence relations considered in the problem contains many cases of combinatorial interest for particular choices of the six parameters that define it. We give a complete classification of the partial differential equations satisfied by the exponential generating functions, and solve them in all cases. We also show that the recurrence relations defining the combinatorial numbers appearing in this problem display an interesting degeneracy that we study in detail. Finally, we obtain for all cases the corresponding univariate row generating polynomials.We are indebted to Alan Sokal for his participation in the early stages of this work, and his encouragement and useful suggestions later on. We also thank Jesper Jacobsen, Anna de Mier, Neil Sloane, and Mike Spivey for correspondence, and David Callan for pointing out some interesting references to us. This research has been supported in part by Spanish MINECO grant FIS2012-34379. The research of J.S. has also been supported in part by Spanish MINECO grant MTM2011-24097 and by U.S. National Science Foundation grant PHY-0424082

Coating ZnO:Zn Nanoparticles with Alumina for Polymer Protection

Using a modified preparation large nanoparticles of ZnO and ZnO:Zn were coated (without destroying the luminescent properties of the latter), but the coating is a layer of AZO not Al2O3. Large nanoparticles of ZnO:Zn were coated with a layer of ZnO by using only (NH4)HCO3 in the absence of Al2SO4

Photoluminescence Study of Symmetry-Related Transitions in the Spectrum of Y2O3:Tb3+

Herein we describe the results of a study on the photoluminescence of cubic nanosized Y2O3:Tb3+. These results confirm our earlier conclusions based on cathodoluminescence about the energy flow from excited Tb3+ in a S6 lattice site to Tb3+ in a C2 sit

Symmetry-related transitions in the spectrum of nanosized Cubic Y2O3: Tb3+

Herein the preparation and cathodoluminescence of nanoparticles of cubic Y2O3:Tb3+ having Tb3+ concentration varying between 0.1 and 10 Mol% are described. The cathodoluminescence spectra were recorded with a high resolution spectrometer, which enabled the identification of Tb3+ lines with C2 and S6 symmetry: the lines at 542.8 nm and 544.4 nm were designated as 5D4→7F5 (C2) and 5D4→7F5 (S6) respectively. The critical distance for energy transfer from Tb3+ ions at S6 lattice sites to Tb3+ ions at C2 lattice sites was found to be >1.7 nm. At the greater distances which prevail at low Tb3+ concentration, this energy transfer virtually stops. From cathodoluminescence spectra recorded in a scanning transmission electron microscope it was concluded that this energy transfer also did not take place if the temperature was reduced below 102 K. The efficiency of the cathodoluminescence of 1% Y2O3:Tb3+ was 6 lm/w at a beam voltage of 15 kV. The decay time of the 5D4→7F5 (C2) transition was substantially shorter than that of the 5D4→7F5 (S6) transition at low Tb3+ concentrations. The decay behavior of the cathodoluminescence images in a field emission scanning electron microscope has been explained in terms of phosphor saturation.We are grateful to the EPSRC and the Technology Strategy Board (TSB) for funding the PURPOSE (TP11/MFE/6/I/AA129F; EPSRCTS/G000271/1) and CONVERTED (JeS no. TS/1003053/1) programs. We are also grateful to the TSB for funding the CONVERT program

Symmetry-related transitions in the photoluminescence and cathodoluminescence spectra of nanosized cubic Y2O3:Tb3+

Herein the photoluminescence spectra of nanosized cubic Y2O3:Tb3+ having Tb3+ concentrations varying between 0.1 and 10 Mol% are described. Low temperature cathodoluminescence spectra from these materials recorded in a scanning transmission electron microscope are presented and discussed. By studying the photoluminescence-spectra recorded at room temperature and focused on the 5D4→7F5 (C2) and 5D4→7F5 (C3i) transitions, at 542.8 and 544.4 nm respectively, it was found that the critical distance for energy transfer from Tb3+ ions at C3i lattice sites to Tb3+ ions at C2 lattice sites was 1.7 nm; at distances >1.7 nm, which prevail at low Tb3+ concentration, this energy transfer virtually stops. The gradual change of the excitation spectra upon increasing the Tb3+ concentration is also explained in terms of energy transfer from Tb3+ at C3i sites to Tb3+ at C2 sites. Cathodoluminescence spectra recorded at low temperatures with the scanning transmission electron microscope provided additional evidence for this radiationless energy transfer.We are grateful to the EPSRC and the Technology Strategy Board (TSB) for funding the PURPOSE (TP11/MFE/6/I/AA129F; EPSRCTS/G000271/1) and CONVERTED (JeS no. TS/1003053/1) programs. The TSB funded the CONVERT program