Pure Blue Electroluminescence by Differentiated Ion Motion in a Single Layer Perovskite Device

Blue electroluminescence is highly desired for emerging light-emitting devices for display applications and optoelectronics in general. However, saturated, efficient, and stable blue emission has been challenging to achieve, particularly in mixed-halide perovskites, where intrinsic ion motion and halide segregation compromises spectral purity. Here, CsPbBr_3−xCl_x perovskites, polyelectrolytes, and a salt additive are leveraged to demonstrate pure blue emission from single-layer light-emitting electrochemical cells (LECs). The electrolytes transport the ions from salt additives, enhancing charge injection and stabilizing the inherent perovskite emissive lattice for highly pure and sustained blue emission. Substituting Cl into CsPbBr₃ tunes the perovskite luminescence from green through blue. Sky blue and saturated blue devices produce International Commission on Illumination coordinates of (0.105, 0.129) and (0.136, 0.068), respectively, with the latter meeting the US National Television Committee standard for the blue primary. Likewise, maximum luminances of 2900 and 1000 cd m⁻², external quantum efficiencies (EQEs) of 4.3% and 3.9%, and luminance half-lives of 5.7 and 4.9 h are obtained for sky blue and saturated blue devices, respectively. Polymer and LiPF₆ inclusion increases photoluminescence efficiency, suppresses halide segregation, induces thin-film smoothness and uniformity, and reduces crystallite size. Overall, these devices show superior performance among blue perovskite light-emitting diodes (PeLEDs) and general LECs.     

Aggregation of lead phthalocyanine in blends with polycarbonate

The blends of a nonlinear optical dye with polycarbonate are described and comparisons are made with solutions of the dye in chloroform. Absorption spectra of blends with up to 1 wt % lead tetracumylphenoxy phthalocyanine showed the dye to be primarily in the monomer form. The monomer absorption spectrum and the measured extinction coefficient replicated those in chloroform solution. As the dye concentration increased to 20 wt %, the monomer intensity decreased and new spectral features characteristic of the dimer appeared. The spectra were resolved into contributions of monomer and dimer, and the concentration effect was analyzed according to the monomer/dimer equilibrium. Much higher monomer concentrations were achieved in polycarbonate blends compared to chloroform solutions. It was concluded that when the blends were quenched from the melt, the equilibrium established at the melt temperature was preserved in the solid state glass. Quenching the blend from different melt temperatures confirmed this interpretation. Extrapolation of the temperature dependent equilibrium constant to 25°C yielded a value close to that reported for chloroform solution at 25°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 104: 464–469, 2007     

Modeling of fretting wear evolution in rough circular contacts in partial slip

This paper presents a numerical model that maps the evolution of contact pressure and surface profile of Hertzian rough contacting bodies in fretting wear under partial slip conditions. The model was used to determine the sliding distance of the contacting surface asperities for one cycle of tangential load. The contact pressure and sliding distance were used with Archard's wear law to determine local wear at each surface asperity. Subsequently, the contact surface profile was updated due to wear. The approach developed in this study allows for implementation of simulated and/or measured real rough surfaces and study the effects of various statistical surface properties on fretting wear. The results from this investigation indicate that an elastic–perfectly plastic material model is superior to a completely elastic material model. Surface roughness of even small magnitudes is a major factor in wear calculations and cannot be neglected.     

Strain tuning of the photocurrent spectrum in single-wall carbon nanotubes

The effect of uniaxial strain on the photocurrent spectrum of semiconducting single-wall carbon nanotubes is measured. The energy of the lowest-lying free electron transition is observed to shift with strain as predicted by a simple noninteracting model. The higher-order transitions also shift with strain, but being excitonic, their strain dependence differs from the predictions for the free carrier states. An anomalous photocurrent increase is also observed near the ground-state transition and is attributed to the formation of optically active defect states within the nanotube band gap.     

On-line simultaneous monitoring of polarization mode dispersion and chromatic dispersion

We have developed new expressions for power fading and average power fading owing to polarization mode dispersion (PMD) and chromatic dispersion in terms of the angle of precession of the output state of polarization about the PMD vector. Based on these expressions, a simple and novel pilot-tone-based technique for simultaneous monitoring of chromatic dispersion and PMD is proposed. Experimental results demonstrate the effectiveness of the proposed technique; these results agree well with the theoretical analysis.     

Field-enhanced photocurrent spectroscopy of excitonic states in single-wall carbon nanotubes

Excitonic and free-carrier transitions in single-wall carbon nanotubes are distinguished using field-enhanced photocurrent spectroscopy. Electric field dissociation allows for the detection of bound-exciton states that otherwise would not contribute to the photocurrent. Excitonic states associated with both the ground-state semiconductor and the ground-state metallic nanotube transitions are resolved. The observation of a metallic excitonic state corroborates recent predictions of a symmetry gap existing in metallic nanotubes.     

Synthesis of <Emphasis Type="Italic">c</Emphasis>-Axis Barium Hexaferrite Puck for Communication Application

Recent progress and needs by telecommunication industries require thick barium ferrite film with excellent magnetic properties for microwave monolithic integrated circuit applications. In the present work we show a novel barium hexaferrite (BaFe₁₂O₁₉, or BaM) composite material, BaFe₁₂O₁₉ nanopowder mixture with epoxy, as a low-cost solution to fabricate thick BaM films. The mix is used to fabricate thick puck of BaM within an alumina substrate. The resulting barium hexaferrite thick pucks have good magnetic properties with a magnetization saturation 4πMs between 2000 and 2500 Gauss, a perpendicular coercivity of 3800 to 4000 Oe and a close to 0.9 squareness. In addition, we have successfully fabricated and tested a self-biased microwave circulator by depositing and patterning copper contact lines on the alumina substrate and the BaM thick puck.     

The Relative Activation Energy of Food Materials: Important Parameters to Describe Drying Kinetics

An effective drying model should be accurate and require a small number of experiments to generate the parameters. The relative activation energy of various food materials, important drying kinetic properties used in the reaction engineering approach, is evaluated and summarized. The reaction engineering approach is then implemented to model the global and local drying rates of food materials. By using the relative activation energy, the reaction engineering approach describes the (R² higher than 0.99) global drying rate of food materials well. The reaction engineering approach can be coupled with a set of equations of conservation of heat and mass transfer to model the local drying rate of food materials. The relative activation energy is indeed proven to be accurate to model the local drying rate. While the predictions are accurate, the reaction engineering approach is very effective in generating the drying parameters since the relative activation energy can be generated from one accurate drying run. Different drying conditions of the same material with similar initial moisture content would result in the similar relative activation energies. The drying kinetics parameters generated here are readily used for design of new equipment, evaluating the performance of existing dryers, and monitoring the product quality.     

Computational Approaches for Studying the Granular Dynamics of Continuous Blending Processes, 2 – Population Balance and Data‐Based Methods

The application of computationally inexpensive modeling methods for a predictive study of powder mixing is discussed. A multidimensional population balance model is formulated to track the evolution of the distribution of a mixture of particle populations with respect to position and time. Integrating knowledge derived from a discrete element model, this method can be used to predict residence time distribution, mean and relative standard deviation of the API concentration in a continuous mixer. Low‐order statistical models, including response surface methods, kriging, and high‐dimensional model representations are also presented. Their efficiency for design optimization and process design space identification with respect to operating and design variables is illustrated.