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55.3: One‐step extruding method for fabricating perovskite quantum dot light diffusers

All‐inorganic perovskite quantum dots (PQDs) exhibit excellent physics properties and application prospects in the field of LED lighting applications and display devices. However, poor long‐term stability to light irradiation, water, heat, and oxygen hinders the further development of commercialization. Using polymer plastics, such as PS (polystyrene), PC (polycarbonate), PMMA (polymethyl methacrylate), PP (polypropylene), as the matrix along with proper Cs, Pb and halogen (X) sources as perovskite precursors, CsPbX3 PQDs/polymer composites can be synthesized via a solvent‐free and in‐situ polymeric melt encapsulation method. Special attention was paid to the effects of growth conditions on the photoluminescent quantum yield (PLQY) of the composites. The optimized CsPbX3 PQDs/polymer composite demonstrated excellent performance with more than 90% PLQY and 22 nm full width at a halfmaximum (FWHM) for green and 35 nm FWHM for red. Particularly, we combined this in‐situ melting synthesis technology with industrial production, and used a melting extruder to directly fabricate perovskite quantum dot optical diffuser products for backlight display. Under the protection of multi‐layer structure, the PQD diffusers exhibited remarkable long‐term stability. This study provides a novel solvent‐free and in‐situ synthesis route for fabricating diffuser products, which is quite friendly to industrialization and commercialization for perovskite materials.

Flexible White Lighting Fabricated With Quantum Dots Color Conversion Layers Excited by Blue Organic Light-Emitting Diodes

In this study, HATCN is coated on flexible PET/indium tin oxide (ITO) substrate as a modified layer and a hole injection layer to improve the hole injection from ITO. Then a blue organic light emitting diode (OLED) can successfully be fabricated without a surface treatment procedure (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> plasma or UV Ozone treatment). The new blue TADF series fluorescent material is employed as emitting layer with a luminescence wavelength of 456 nm. Also, it has a narrow full width at a half maximum (FWHM) of 26 nm featuring excellent color chromaticity. Quantum dot (QD) photoresist is a perfect color conversion material featuring good color adjustability, narrow emission spectrum, high luminous efficiency, and simple spin-coating processes. In this study, the photoresist mixed with green and red quantum dots is used as a color conversion layer (CCL), and a blue OLED is utilized to excite green and red CCL. To test the material of QD photoresist, it is coated on the substrate of another piece of glass first and then the blue OLED is utilized to remotely excite green and red QD CCL. The fluorescence characteristic of QD photoresist is explored to acquire a spectrum of 528 nm and 620 nm. In the device structure of a blue OLED, the electron-and hole-only current density is compared and the hole transport layer TAPC thickness is adjusted to improve the luminance and efficiency. Finally, green and red quantum dot photoresist is mixed using a proper ratio and then directly coated on the back of the PET/ITO substrate. Furthermore, the thickness of the QD photoresist is adjusted to increase the QD excited fluorescence. The blue OLED and QD CCL was integrated to generate three primary colors, i.e., blue, green, and red. Finally, a flexible white OLED lighting panel is successfully fabricated using simple processes. Moreover, it features high-spectrum stability. The CIE coordinates will not drift with bias, thus, it can resist the voltage variation.

One‐Step Polymeric Melt Encapsulation Method to Prepare CsPbBr3 Perovskite Quantum Dots/Polymethyl Methacrylate Composite with High Performance

AbstractAll‐inorganic CsPbBr3 perovskite quantum dots (PQDs) exhibit excellent photoelectric properties and application prospects in the field of light‐emitting diodes (LEDs) and display devices. However, these possess poor long‐term stability to UV irradiation, water, heat, and oxygen. Using polymethyl methacrylate (PMMA) as the matrix along with CH3(CH2)16COOCs, [CH3(CH2)16COO]2Pb, and KBr as the perovskite sources, CsPbBr3 PQDs/PMMA composites are for the first time prepared via an in situ polymeric melt encapsulation method. Special attention is paid to the effects of synthesis conditions on the photoluminescent quantum yield (PLQY) of the composites. The optimized CsPbBr3 PQDs/PMMA composite reveals excellent performance with ≈82.7% PLQY and ≈18.6 nm full width at a half‐maximum (FWHM). In particular, after 90 h of UV irradiation or 35 days of heating at 60 °C, the luminous intensity remains almost unchanged. In addition, after soaking in water for 15 days, it retains up to ≈53% of the initial luminous intensity, meaning that the composite possesses long‐term stability to UV irradiation, heat, and water. The as‐prepared white LED (WLED) based on the composite evidences the wide color gamut (126.5% National Television System Committee (NTSC)) and a luminous efficiency of 32 lm W−1. This work offers a novel, easily industrialized one‐step, and solvent free route for low‐temperature synthesis of all‐inorganic PQDs with broad application prospects.

Multi-resolution multi-sensitivity design for parallel-hole SPECT collimators

Multi-resolution multi-sensitivity (MRMS) collimator offering adjustable trade-off between resolution and sensitivity, can make a SPECT system adaptive. We propose in this paper a new idea for MRMS design based on, for the first time, parallel-hole collimators for clinical SPECT. Multiple collimation states with varied resolution/sensitivity trade-offs can be formed by slightly changing the collimator’s inner structure. To validate the idea, the GE LEHR collimator is selected as the design prototype and is modeled using a ray-tracing technique. Point images are generated for several states of the design. Results show that the collimation states of the design can obtain similar point response characteristics to parallel-hole collimators, and can be used just like parallel-hole collimators in clinical SPECT imaging. Ray-tracing modeling also shows that the proposed design can offer varied resolution/sensitivity trade-offs: at 100 mm before the collimator, the highest resolution state provides 6.9 mm full width at a half maximum (FWHM) with a nearly minimum sensitivity of about 96.2 cps MBq−1, while the lowest resolution state obtains 10.6 mm FWHM with the highest sensitivity of about 167.6 cps MBq−1. Further comparisons of the states on image qualities are conducted through Monte Carlo simulation of a hot-spot phantom which contains five hot spots with varied sizes. Contrast-to-noise ratios (CNR) of the spots are calculated and compared, showing that different spots can prefer different collimation states: the larger spots obtain better CNRs by using the larger sensitivity states, and the smaller spots prefer the higher resolution states. In conclusion, the proposed idea can be an effective approach for MRMS design for parallel-hole SPECT collimators.

Highly c-axis oriented growth of GaN film on sapphire (0001) by laser molecular beam epitaxy using HVPE grown GaN bulk target

Growth temperature dependant surface morphology and crystalline properties of the epitaxial GaN layers grown on pre-nitridated sapphire (0001) substrates by laser molecular beam epitaxy (LMBE) were investigated in the range of 500–750 °C. The grown GaN films were characterized using high resolution x-ray diffraction, atomic force microscopy (AFM), micro-Raman spectroscopy, and secondary ion mass spectroscopy (SIMS). The x-ray rocking curve full width at a half maximum (FWHM) value for (0002) reflection dramatically decreased from 1582 arc sec to 153 arc sec when the growth temperature was increased from 500 °C to 600 °C and the value further decreased with increase of growth temperature up to 720 °C. A highly c-axis oriented GaN epitaxial film was obtained at 720 °C with a (0002) plane rocking curve FWHM value as low as 102 arc sec. From AFM studies, it is observed that the GaN grain size also increased with increasing growth temperature and flat, large lateral grains of size 200-300 nm was obtained for the film grown at 720 °C. The micro-Raman spectroscopy studies also exhibited the high-quality wurtzite nature of GaN film grown on sapphire at 720 °C. The SIMS measurements revealed a non-traceable amount of background oxygen impurity in the grown GaN films. The results show that the growth temperature strongly influences the surface morphology and crystalline quality of the epitaxial GaN films on sapphire grown by LMBE.

The mechanism of the photoluminescence changes in bio-conjugated CdSe/ZnS quantum dots

The change of the photoluminescence (PL) and optical characteristics in non-conjugated and conjugated with S6K2 antibody CdSe/ZnS core/shell quantum dots (QDs) during storage in air has been studied by the conventional PL, micro-PL and micro-Raman techniques. The QDs dried on a crystalline Si substrate were kept in the darkness and under illumination. In the PL spectra, the storage resulted in a blue shift of PL peak position, in the increasing of the full width at a half maximum (FWHM) of the PL band and in the decreasing of the PL intensity. In the Raman spectra, the shift of the CdSe LO peak position to the low frequency region and the increasing of its FWHM were observed. The transformations in the PL and optical characteristics correlate with each other and are found to be the largest in bio-conjugated QDs stored under illumination. The increase of the light intensity accelerated the changes occurred during storage. An oxidation of the QD core, which decreases the QD size, is supposed to be responsible for observed transformations. The bio-conjugation is assumed to promote QD oxidation that results in different PL peak position in stored non-conjugated and bio-conjugated QDs. The mechanism of the effect is discussed.

Computed Tomography to Estimate the Representative Elementary Area for Soil Porosity Measurements

Computed tomography (CT) is a technique that provides images of different solid and porous materials. CT could be an ideal tool to study representative sizes of soil samples because of the noninvasive characteristic of this technique. The scrutiny of such representative elementary sizes (RESs) has been the target of attention of many researchers related to soil physics field owing to the strong relationship between physical properties and size of the soil sample. In the current work, data from gamma-ray CT were used to assess RES in measurements of soil porosity (ϕ). For statistical analysis, a study on the full width at a half maximum (FWHM) of the adjustment of distribution of ϕ at different areas (1.2 to 1162.8 mm2) selected inside of tomographic images was proposed herein. The results obtained point out that samples with a section area corresponding to at least 882.1 mm2 were the ones that provided representative values of ϕ for the studied Brazilian tropical soil.

Influence of transmitted-laser linewidth on sensitivity and error of double-edge wind lidars

We present the results of study of the influence of the transmitted-laser linewidth on the measurement sensitivity and error of a double-edge incoherent wind lidar. The quantitative relationship between the transmitted-laser linewidth and the full width at a half maximum (FWHM) of the backscattered spectrum was simulated using the Monte Carlo method, because such relationship cannot be given by an analytic formula. The quantitative relationship was fitted using a quadratic fit and was further employed for calculating the measurement sensitivity and error. The FWHM of the backscattered spectrum increased from 3.884 GHz to 5.407 GHz, while the transmitted-laser linewidth increased from a monochromatic one to 2 GHz. The measurement greatly suffered from the broadening of the transmitted-laser linewidth. The measurement sensitivity decreased from 0.0031 to 0.0019 and the measurement error increased from 0.326 m/s to 0.524 m/s, while the signal-to-noise ratio and laser shots were both 1000.

Implementation of Hot-Wall MOCVD to the Growth of High-Quality GaN on SiC

This paper reports on the growth of high-quality GaN layers on Si C substrates by hot- wall MOCVD. Use of AlN buffer with a thickness exceeding 50 nm is employed for the GaN deposition and it is found to encompass most of the misfit defects. A n arrower X-ray rocking curve over asymmetric than over symmetric reflection is measured - full width at a half maximum (FWHM) of 350 arcsec vs. FWHM of 490 arcsec for 10.4 and 00.2 peaks, respectively, indicating high overall quality of the film. The free exciton photoluminescence emission peak has rather narrow FWHM of 5 meV. The typical thickness of the GaN layers is about 2 mm and they are completely depleted according to the capacitance-voltage profili ng, which corresponds to estimated residual doping of less than 5x10 14 cm -3 . Only in some cases when the GaN layer is not depleted, deep level transient spectroscopy is performed and two deep traps with activation energies of 0.26 and 0.59 eV below the conduction band are measured.

PbTiO3 epitaxial thin films as optical waveguides

Thin films of lead titanate (PbTiO 3 -PT) have been prepared in-situ on SrTiO 3 (100) substrates using radio-frequency sputtering. The epitaxial quality of the films has been investigated as a function of the substrate temperature. Stoichiometric films have been obtained in the temperature range 550°C-600°C. Films have a high degree of c-axis oriented crystalline structure. The optimum conditions for growing epitaxial PbTiO 3 layers are reported in this study. Thin films grown at 550°C exhibited a rocking curve full width at a half maximum (FWHM) of 0.26°. The refractive index calculated from optical transmission method has been evaluated to 2.61 @ 632.8nm. which represents 98% of the corresponding bulk material.

GaN grown by hydride vapor phase epitaxy on p-type 6H-SiC layers

6H-SiC/GaN pn-heterostructures were grown by subsequent epitaxial growth of p-SiC by low temperature liquid phase epitaxy (LTLPE) and n-GaN by hydride vapor phase epitaxy (HVPE). For the first time, p-type epitaxial layers grown on 6H-SiC wafers were used as substrates for GaN HVPE growth. The GaN layers exhibit high crystal quality which was determined by x-ray diffraction. The full width at a half maximum (FWHM) for the ω-scan rocking curve for (0002) GaN reflection was ∼120 arcsec. The photoluminescence spectra for these films were dominated by band-edge emission. The FWHM of the edge PL peak at 361 nm was about 5 nm (80K).

Preparation of a-axis-oriented YBa 2Cu 3O x superconducting films on MgO substrates with PrBa 2Cu 3O x buffer layers

We prepared high-quality a-axis-oriented superconducting YBa 2Cu 3O x (YBCO) films on (100)MgO substrates using the c-axis-oriented PrBa 2Cu 3O x (PBCO) buffer layer and the a-axis-oriented cubic YBCO self-template layer. The YBCO template layers deposited at a low substrate temperature ( T s) on MgO substrates without the PBCO buffer layers were found to turn into orientation other than a-axis orientation by annealing at a higher temperature after the deposition. The in-plane aligned c-axis-oriented PBCO layer was inserted between the a-axis-oriented cubic YBCO layer and the MgO substrate to stabilize the template layer. As a result, the YBCO film deposited at higher T s on these layers was found to be a-axis-oriented with a full width at a half-maximum (FWHM) of the (200) rocking curve of 0.58°, an FWHM of (200) diffraction of 0.18°, a critical onset temperature around 90 K and a critical zero temperature of 70 K.