Qijin Cheng

A novel high color purity yellow luminescent material NaBaBO3:Sm3+

Yellow emitting Sm3+-doped NaBa1-xBO3(0.01 ≤ x ≤ 0.13) phosphors were synthesized by conventional solid state reaction method. The phase structure and luminescence properties of the as-prepared phosphors were investigated. These phosphors can be effectively excited by 403 nm near-ultraviolet light and feature a satisfactory yellow performance. The emission peaks are observed at 560 nm, 603 nm and 650 nm, originating from the transitions of 4G5∕2→6H5∕2, 4G5∕2→6H7∕2 and 4G5∕2→6H9∕2 respectively. Investigation of Sm3+ concentration-dependent emission spectra indicates that the NaBa0.95BO3:0.05Sm3+ phosphor shows the strongest yellow emission intensity and exhibits the CIE value of x = 0.4760 and y = 0.5090. Through the theoretical calculation, a high color purity of 96.0% was determined for the NaBaBO3:Sm3+ phosphor, and the color purity of NaBaBO3:Sm3+ is much higher than that of the commercial yellow phosphor YAG:Ce3+. This work is highly relevant to the development of a new type of potential down-conversion (DC) yellow phosphor for near ultraviolet white or yellow light-emitting diodes (LEDs).

Luminescence properties and first principles calculations of Dy3+ activated Sr3B2O6 phosphors

A novel white-light-emitting Sr3B2O6:Dy3+ phosphor was prepared by solid-state reactions and its luminescence properties were investigated. The excitation spectrum of obtained phosphor monitored at 479 nm covers a very broad spectral region from 320 nm to 460 nm with peaks at 323, 349, 363, 386, 427 and 456 nm. Under excitation at 349 nm, the phosphor exhibits a blue emission centered at 479 nm and a yellow emission centered at 574 nm. The optimal doping concentration of Dy3+ is obtained to be 7 mol%, and the concentration quenching is observed when the concentration of Dy3+ exceeds 7 mol%. This concentration quenching is due to the enhanced energy exchange among Dy3+ ions. The CIE chromaticity coordinate (0.289, 0.302) of Sr3-0.07B2O6:0.07 Dy3+ located in the white-light region can be achieved. Theoretical calculations of electronic properties for Sr3B2O6:Dy3+ phosphor in the framework of the density functional theory (DFT) were carried out. Our results suggest that the Sr3B2O6:Dy3+ phosphor is a promising single-component white-light-emitting material.

GaN light-emitting diodes with an Al-coated graphene layer as a transparent electrode

We fabricated GaN light-emitting diodes with a layer of graphene as a transparent electrode. A 3-nm-thick Al layer was deposited on the graphene layer by electron-beam evaporation. This Al layer plays an important role in protecting the graphene layer during the device fabrication process. Moreover, this Al layer can also enhance the light emission of GaN light-emitting diodes through the investigation of electroluminescence spectra. The significantly improved light emission is attributed to the current expansion, the enhanced plasmonic density of states, and the decreased non-radiative recombination rate.

The Preparation and Microstructure of Nanocrystal 3C-SiC/ZrO2 Bilayer Films

The nanocrystal 3C-SiC/ZrO2 bilayer films that could be used as the protective coatings of zirconium alloy fuel cladding were prepared on a single-crystal Si substrate. The corresponding nanocrystal 3C-SiC film and nanocrystal ZrO2 film were also dividedly synthesized. The microstructure of nanocrystal films was analyzed by grazing incidence X-ray diffraction (GIXRD) and cross-sectional transmission electron microscopy (TEM). The 3C-SiC film with less than 30 nm crystal size was synthesized by Plasma Enhanced Chemical Vapor Deposition (PECVD) and annealing. The corresponding formation mechanism of some impurities in SiC film was analyzed and discussed. An amorphous Zr layer about 600 nm in width was first deposited by magnetron sputtering and then oxidized to form a nanocrystal ZrO2 layer during the annealing process. The interface characteristics of 3C-SiC/ZrO2 bilayer films prepared by two different processes were obviously different. SiZr and SiO2 compounds were formed at the interface of 3C-SiC/ZrO2 bilayer films. A corrosion test of 3C-SiC/ZrO2 bilayer films was conducted to qualitatively analyze the surface corrosion resistance and the binding force of the interface.

Enhanced Carrier Collection in Silver Nanoparticle Embedded Zinc Oxide Nanorod Top Electrodes for Thin-Film Photovoltaic Devices

Cu(In, Ga)Se2 solar cells are the representative of high efficient thin-film solar cell with energy conversion efficiency of over 22%. However, nowadays, top electrodes of solar cells gradually become the performance limitation for optimized devices. The Al-doped ZnO thin film is widely used as a transparent top electrode in Cu(In, Ga)Se2, but there are still some techniques and electrical property issues. In this letter, we establish a ZnO/Ag/ZnO:Al multilayer top electrode, composed of ZnO nanorod arrays, Ag nanoparticles, and ZnO:Al thin films. Such multilayer top electrode was applied on Cu(In, Ga)Se2 thin-film solar cells and the devices yield a higher efficiency from 6.79% to 8.52%. Importantly, we also propose that the enhanced electronic carrier concentration in such ZnO/Ag/ZnO:Al top electrode aids the performance of solar cells. Therefore, well-designed ZnO-based top electrodes offer the opportunity to remove the bottleneck of improving the solar cell efficiency.

The applied research and solar simulation spectral design based on pulse xenon lamp with coating film

In the paper the spectrum of realistic sunlight and pulse xenon lamp were compared to each other, the result shows that the infrared part of luminescence spectrum of xenon lamp without coating film occupies the total spectrum’s 57.4%, but the infrared part of the standard solar spectrum only reaches to 28.3%. The transmittance curve of pulse xenon lamp is got by fitting. Using appropriate method and coating film parameter, the film is done to pulse xenon lamp, and the negative film coefficient transmittance is 16% is got at 935nm central wavelength. At the range of 400-760nm wavelength the average transmittance is more than 86%, and the average transmittance is more than 96% at the range of 400-760nm wavelength. A portion of infrared light can be filtered after coating film. By the spectral testing of two coating film xenon lamp, it can be found that the spectral matching rate is from 0.792 to 1.176 and it is satisfied to A grade standard request. By using A and C grade pulse xenon lamp electric performance of 40.5W thin film cell is tested and the power value by C grade simulative light source is lower than real power for 11.2W. The result indicates the spectral matching rate of solar simulator is very important for cell electric performance.