bluuebunny/crossref_metadata_2025_split huggingface dataset:
Engineering of Rare-Earth-Metal Oxysulfate (RE2O2SO4) Hollow Nanospheres for Upconversion
Authors: Chen Gen , Yan Litao , Luo Hongmei 
Published: February 2020

Bulk glass and crystalline materials are usually used for upconversion, but bulk materials are often not suitable for certain applications such as biological imaging or biolabelling. Upconversion materials on nanometer scales are desirable. However, synthesis of small nanocrystals that exhibit high monodispersibility and excellent upconversion properties remains a challenge.
In this work, nanoscale monodisperse rare-earth-metal-doped oxysulfate RE2O2SO4 (RE = Y, Gd) hollow spheres were prepared for upconversion via a biomolecule-assisted hydrothermal method followed by calcination. The size and crystallinity of nanospheres, as well as the upconversion properties could be tuned by changing the experimental conditions such as surfactants, hydrothermal/annealing temperature, and chemical compositions. Upconversion properties revealed that the energy transfer between the sensitizer and the activator was strongly depended on the concentration of activator, the ratio of sensitizer to activator, chemical compositions and crystallinity of the hollow spheres.
Improvement of Luminescence Properties and Particle Growth of AlN Phosphors By Si-Doping
Authors: Cho Yujin , Dierre Benjamin , Fukata Naoki , Hirosaki Naoto , Takahashi Kohsei , Takeda Takashi , Sekiguchi Takashi 
Published: February 2020

Aluminum Nitride (AlN) has been regarded as a promising material for ceramic phosphors. Recently, we have developed a high efficiency blue AlN phosphor by co-doping with Si and Eu [1-2]. It has been proven that particle have grown rapidly with the highest luminescent intensity on the proper Si doping. Now, it is important to understand the role of Si on AlN particle growth and luminescence enhancement.
For this purpose, AlN powders doped with Si from 0 to 4 at. % were prepared using gas-pressure sintering (GPS) furnace at 1950°C in N2 atmosphere. Firstly, particle size, phases and luminescence spectra of Si-doped AlN powder were investigated using SEM, XRD and CL. Secondly, the defect were evaluated by EPR to identify the defects transitions. Finally, the particle growth mechanism was clarified by cross-sectional CL-EDS.
From 0.4 to 2.0 % Si, particle growth of AlN powders as well as ultraviolet emissions at 290 and 350 nm are enhanced. The 350 nm emission may be attributed to native AlN defects such as vacancy-oxygen complexes. The shoulder at 290 nm and 450 nm can be ascribed to the different states of Si related defects in AlN by EPR analysis. Cross sectional CL images show that the 1.6 % Si-doped AlN yields 280 nm emission at the surfaces of AlN particles (Fig. 1). Many particles are connected to each other with these bright surfaces. It suggests that the Si-rich surface may act as the binder of AlN particles and enhance the Ostwald growth.
References:
[1] T. Takeda et al., J. Mater. Chem., 20, 9948 (2010).
[2] B. Dierre et al., ECS J. Solid State Sci. Technol., 2, R126 (2013).
Figure:
Cross sectional SE (a), CL images taken at 280 nm (b), 350 nm (c) for 1.6% Si-doped AlN powders and schematics explanning the growth mechanism (d))

Figure 1
Inverse Nephelauxetic Effect in the Pressure Dependence of R-Line Energy of Ruby
Authors: Ogasawara Kazuyoshi , Novita Mega 
Published: February 2020

Recently Mn4+-doped materials are drawing attention as candidates for novel red phosphors for white LED. Therefore, understanding the factors which determine the multiplet energies of d3 ions such as Mn4+ and Cr3+ in crystals is quite important. Experimentally the R-line (2E) energy of ruby (Cr3+:α-Al2O3) shows a redshift under pressure. However, this seems to be inconsistent with the interpretation based on the ordinary “Nephelauxetic effect.” When the applied pressure increases, the molecular orbitals mainly consisting of Cr 3d should contract. Therefore, the Coulomb repulsion among d electrons increases and the energy of 2E, which belongs to (t2g)3configuration, should increase.
In order to clarify the origin of this discrepancy, we have performed first-principles calculations of multiplet energies of ruby under various pressures. The structural optimization around the impurity Cr3+ ion in α-Al2O3 under pressure was performed using the CASTEP code. The model clusters consisting of 63 atoms were constructed based on the optimized structure and multiplet calculations were performed using the DVME code. The underestimation of electron correlation effects were corrected by the configuration dependent correction (CDC) and the correlation correction (CC). In order to clarify the factors which determine the behavior of 2E energy, the effect of covalency and the effect of correlation correction were investigated quantitatively based on the Coulomb integrals.
The results show that the pressure dependence of 2E energy was well reproduced by the first-principles calculations. The detailed analysis indicated that the Coulomb integral of t2g orbital increases for higher pressure as expected from the contraction of the molecular orbitals. However, due to the strong electron correlation effect, the effective Coulomb integral of t2g orbital significantly decreases, resulting in the decrease of 2E energy. This behavior is opposite to the prediction from the ordinary Nephelauxetic effect and can be called an “Inverse Nephelauxetic effect.”
Assessing Spatial Resolution of Cathodo-Luminescence Imaging and Spectroscopy at the Nanoscale for Inorganic Phosphor Powders
Authors: Fern George Robert , Harris Paul Gregory , Ireland Terry , Silver Jack 
Published: February 2020

It is now possible to easily collect CL images (using a photomultiplier tube using total or filtered light) and emission spectra from individual nanometer sized particles using the commercially available Gatan Vulcan attachment for a transmission electron microscope (TEM). In our case, at Brunel University London, we have fitted this to a JEOL 2100F field emission TEM. This work demonstrates the spatial resolution that has been achieved when imaging various phosphor nano materials and discusses the limitations of the technique. It also demonstrates the uniformity of excitation/emission from various phosphors, and hence the effectiveness of the synthetic method used to manufacture the phosphor can be seen. Conventionally, photoluminescence (PL) and cathodoluminescence (CL) spectra are collected from bulk phosphor samples and are the average of all of the particles in the sample. This is true of most samples made either in the laboratory for research or commercial materials prepared by industrial companies. Cathodoluminescence spectra have been collected from nanometer-sized crystals of quantum dots (spherical and rods) and various oxide and oxysulfide phosphors. The latter phosphors have been implemented into CL applications on a vast scale whereas the quantum dot materials are not designed for CL application and therefore great care is required when imaging these materials to minimize the effect of beam damage.
When observing mixtures of phosphors (Gd2O2S:Tb3+ and Y2O3:Eu3+) it is apparent that when the electron beam is positioned onto one of these two materials and the spectrum observed, then the other phosphor emission spectrum can be observed if the particles are nearby. However when observing quantum dot materials the spatial resolution is only limited by the particle size. A tentative explanation for this effect is given.
In this work we compare the spectra of nanometer sized phosphor crystals/particles in order to understand any variation in the emission spectra between the phosphor grains and to understand the effect of temperature on their luminescent properties.
Our results will be presented that could only have been found by using CL spectra obtained directly from single nanoparticles. In conclusion:
1) The effect of different TEM machine parameters will be discussed
2) The CL spatial resolution will be demonstrated
Figure 1. Left) HAADF STEM of nanometre-sized single crystals of Y2O3Eu3+ and Gd2O2S:Tb3+; The green line spectrum image shows where 10 emission spectra were recorded at equally spaced intervals. Right) Extracted spectra taken from opposite ends on the line scan show the characteristic CL emission spectrum for both the Eu3+ and Tb3+ are observed in both spectra.

Figure 1
Thermal Degradation of Nitride Phosphors
Authors: Xie Rong-Jun , Wang Chunyun , Takeda Takashi , Cho Yujin , Suehiro Takayuki , Hirosaki Naoto 
Published: February 2020

Thermal stability of phosphors for solid state lighting is usually investigated by in-situ measuring the thermal quenching behavior of the sample heated up to ~ 300oC and held at each temperature for a certain time. However, thermal quenching does not have the same meaning with thermal degradation, which thus cannot evaluate the stability of the phosphor against thermal attacks comprehensively. In this work, we attempted to study the thermal degradation of nitride phosphors (i.e., SrSi2O2N2:Eu and CaAlSiN3:Eu) by baking the powders in air or in pressued water steam at high temperatures. The degradation mechanism was discussed and clarified by carrying out the surface state analysis using various techniques.
For SrSi2O2N2:Eu, the PL intensity decreased as the baking temperature rises, degrading by 10 and 30% when the samples baked at 500 and 600oC, respectively. In comparison with Ca-α-sialon:Eu2+ that retained its luminescence up to 800oC, SrSi2O2N2:Eu showed a very serious thermal degradation. By conducting the high-temperature in-situ XRD analysis and TEM observations, an impurity phase of SrSiO3 was identified additionally, as a result of the oxidation of the host SrSi2O2N2. In addition, the activator ions were also oxidized during baking in air, with divalent Eu2+ changed into trivalent Eu3. It indicates that both of the oxidation of host and activators leads to the thermal degradation of SrSi2O2N2:Eu that is an irreversible decrease of luminescence.
For (Sr,Ca)AlSin3:Eu (SCASN), the moisture-induced degradation was comprehensively investigated by treating it under a severe condition of high-pressure water steam. The degradation initiated at 150oC, and the luminescence of SCASN was seen to be quenched quickly, with the powder sample being bleached after the treatment. Both of the microstructure and phase changed obviously with the oxidation, and the host turned finally into NH3, (Sr,Ca)Al2Si2O8 and Ca(OH)2. By using a variety of spectroscopic, surface and microstructure analytic techniques, the degradation mechanism was clarified and proposed to occur viathe oxidant-gas penetration mechanism through the moisture-enhanced oxidation of both the SCASN host and divalent europium.
References:
1. C.Y. Wang, R.-J. Xie, F.Z. Li, and X. Xu, J. Mater. Chem. C. 2, 2735 (2014).
2. J. Zhu, L. Wang, T. L. Zhou, Y.J. Cho, T. Suehiro, T. Takeda, M. Lu, T. Sekiguchi, N. Hirosakia, and R.-J. Xie, J. Mater. Chem. C. 3, 3181 (2015).
The Exploration of Rare Earths Based Luminescence for Detection and Sensing in Radiation Security and Enhanced Oil Recovery
Authors: Chen Wei , Ma Lun , Sahi Sunil 
Published: February 2020

Dirty bomb or radiation attack is a big threat to the world and the developing of high sensitive technologies for radiation detection is an emerging need. Also, the development of high-performance scintillating materials is essential for precision calorimetry in high energy physics, medical imaging and industries. The most frequently considered characteristics of scintillators are efficiency of energy conversion, stopping power, luminescence decay time, spatial resolution, and physical and chemical stability. Currently applied inorganic crystalline scintillators are not only limited by their high cost and scalability issues, but also limited by other intrinsic drawbacks. For example, high purity germanium must be operated at liquid nitrogen temperature, while sodium iodide crystal is highly hygroscopic. On the other hand, plastic scintillators based on polymeric materials are cheap and easy to manufacture, but have low light yield and low density. In this talk, I will present the strategy for how to design luminescence nanomaterials based on energy transfer for radiation detection.
Oil exploration and production are always the hot area as natural oil is still the major energy for our society. Luminescence materials may play an important role in oil exploration and extraction either as water tracers or as new materials for wettability enhancement. In addition, food quality and safety are related to our daily life. In this talk, I also present some new ideas and methods for the potential applications of luminescence materials for oil recovery and food safety.
Amber Full Conversion Ceramics for LED Applications
Authors: Zheng Yi , Montaner Jason , Raukas Madis , Tarry Chris , Kechele Juliane , Tragl Sonja , Strube-Knyrim Johanna , Eisert Dominik , Ferstl Klemens , Goeoetz Britta 
Published: February 2020

Monochromatic amber light-emitting diodes (LEDs) have been widely adopted in the industrial and automotive applications. Although relatively efficient in room temperature, efficacy of direct AlGaInP amber LEDs suffers at higher application temperatures. The phosphor-converted LEDs overcome this drawback by generating amber light from all-nitride ceramic phosphor excited by an efficient blue InGaN chip. At room temperature and 700 mA drive current, the LED using such technique achieves a typical brightness of 135 lm. At application temperatures of 85 °C (Tj in the chip), the LED still achieves the impressive figure of 123 lm. In this talk, the effects of composition, phases and microstructure of (Sr,Ba)2Si5N8:Eu full conversion ceramic phosphors on the color binning, efficacy, thermal quenching and lifetime of phosphor-converted amber LEDs are discussed generally.
Square Wave Voltammetric Method for Simultaneous Determination of Bleaching Agents in Skin Cosmetics
Authors: Calaça Giselle Nathaly , Machado Silvane , Wohnrath Karen , Pessoa Christiana Andrade , Nagata Noemi 
Published: February 2020

Skin pigmentation disorders due to melanin excess, could have different causes. Kojic acid (KA) and hydroquinone (HQ) are depigmenting agents widely associated in pharmaceutical formulations to treat skin pigmentation disorders. An electroanalytical method was developed for simultaneous determination of these bleaching agents in skin whitening cosmetics. Cyclic voltammetry (CV) and square wave voltammetry (SWV) experiments were performed using a potentiostat/galvanostat µAutolab (Type III, Metrohm-Eco Chemie). A conventional three-electrode cell containing a glassy carbon (GCE) as working electrode (A=7,07 mm2), Pt disc (A=12,57 mm2) as counter electrode and Ag/AgCl (saturated aqueous KCl) as reference electrode were employed. Before use and between potential scans, the GCE surface was polished. Kojic acid exhibits a well-defined irreversible oxidation peak at 0.72V and hydroquinone a quasi-reversible redox peaks at 0.08 V and -0.02 V, characterized by adsorptive and diffusional processes, respectively. The influence of the pH was examined over the pH range from 2 until 8 in 0.04 mol L-1 Britton-Robinson buffer solution, the KA and HQ peaks potential shifts negatively with the increase of the pH value, due to the participation of protons in the oxidations processes. Others buffer solutions were examined at pH 8 and Mcllvaine was chosen to subsequent analytical purposes. The square wave voltammetric parameters were optimized by 23 Full Factorial Design including a central point assayed in quintuplicate. The statistical treatment of the data showed that the main effects and interaction effect of amplitude vs. frequency were significant at 95% confidence level. The best response is obtained at a= 40 mV, f= 40 s-1 and ΔES
= 1mV. Under optimized conditions, the calibration curves were obtained in the concentration ranges of 3.5x10-5 to 2.5x10-4 mol L-1 (R= 0.9996) for kojic acid and 1.5x10-5 to 1.6x10-4 mol L-1 (R= 0.9994) for hydroquinone, with detection limits of 7.84x10-6 mol L-1 and 3.71x10-6 mol L-1 for KA and HQ, respectively. The proposed method was validated under parameters: specificity, linearity, range, limit of detection, limit of quantification, precision (repeatability and intermediate precision) and accuracy considering Brazilian Health Surveillance Agency (ANVISA) and International Conference on Harmonisation (ICH) guidelines. The developed and validated method has been successfully applied to the direct simultaneous determination of these compounds in real samples (gel and cream).
Processing and Properties of Nanocomposite Thin Films for Micro-Solid Oxide Fuel Cell Applications
Authors: Rottmayer Michael , Singh Raj , Huang Hong 
Published: February 2020

Microfabricated solid oxide fuel cells (micro-SOFCs) have recently gained attention as a promising technology, with the potential to offer a low temperature (as low as 300oC), reduced start-up time, and improved energy density for portable power applications. As a means for achieving the substantially reduced operating temperatures, new electrode materials with increased catalytic activity are being explored. At present, porous Pt is the most common cathode being investigated for micro-SOFCs. However, there are significant technical challenges for utilizing pure metallic electrodes at the operating temperatures of interest due to their tendency towards Ostwald ripening, as well as low bulk ionic conductivity. Nanocomposite materials (e.g. Pt/YSZ) are being studied as a promising alternative approach for providing both microstructural and electrochemical stability to the electrode layer. The microstructure and composition of the nanocomposite cathode material has been systematically investigated via controlled vacuum deposition conditions and resultant electrochemical properties measured by electrochemical impedance spectroscopy (EIS). Transmission electron microscopy (TEM) of the nanocomposite films reveals a percolating network of Pt and YSZ, along with interconnected nano-sized pores. An improvement in charge transfer kinetics associated with the oxygen reduction reaction has been demonstrated as compared to a pure porous Pt electrode, along with a significant improvement in microstructural stability during extended mSOFC operation. These results will be presented in detail.
Graphene Oxides and Their Hybrids for CO2 Conversion and Solar Fuels
Authors: Chen Li-Chyong , Chen Kuei-Hsien 
Published: February 2020

Finding effective ways for conversion of CO2 into hydrocarbons (as energy fuels or chemical feedstock) is highly desirable to achieve sustainable development. Photocatalytic conversion of CO2 to hydrocarbons such as methanol makes possible simultaneous solar energy harvesting and CO2 reduction, two birds with one stone for the energy and environmental issues. In this talk, I will present our progress in using graphene oxides (GOs), along with their hybrids, as promising photocatalysts for CO2 reduction.
Modified Hummer's method has been applied to synthesize the GOs with tunable band gap. Under visible light, the photocatalytic CO2 to methanol conversion rate on our modified GOs is 0.172 μmol g-cat−1 h−1, which is six-fold higher than the popularly studied TiO2 [Nanoscale
5 (2013) 262]. Meanwhile, a novel one-step and effective electrochemical (EC) method is developed to directly exfoliate graphite into thin reduced graphene oxide (RGO) nanosheets at room temperature. The oxidation degree of the RGOs, hence the C/O ratio, depends on the switching potentials of the EC synthesis. The ability to control the light-absorption of the RGOs by simply adjusting the switching potentials can be further achieved. This approach presents us a possibility for the environmentally friendly, ultrafast, low-cost, and large-scale production of RGOs and great potential in solar-fuel applications.
To enhance carrier generation and separation, therefore the resultant photocatalysis reaction, Cu and MoS2 nanoparticles were further deposited on GOs as co-catalysts. Not only methanol, but also acetaldehyde was detected. Total solar to fuel yield of 6.8 μmole g-cat-1 h-1 has been achieved, which is 170 times enhancement relative to the commercial P-25 photocatalyst [Nano
Lett.
14 (2014) 6097]. In all the above-mentioned hybrids, the photo-catalytic performance is always superior to that of constituent component when used alone. Detailed preparation and characterization of the catalysts will be presented. The role and interplay of the constituent components will also be discussed.
Electrochemical Reactions at Ionic Liquid/Gold Interface Probed By Electrochemical Surface Plasmon Resonance
Authors: Nishi Naoya , Ikeda Yoichi , Amano Ken-ichi , Sakka Tetsuo 
Published: February 2020

Ionic liquids (ILs) are promising materials for electrochemical devices. To maximize the performance of such devices, studies on the interfacial structure, its dynamics, and the kinetics of electrochemical reactions at electrochemical IL interfaces are of crucial importance. Previously we studied the dynamics of the structure at IL|Au interface by using electrochemical surface plasmon resonance (ESPR) [1]. The transient curves of the SPR angle, which reflects the change in the structure in the electrical double layer, showed extraordinarily slow relaxation on the order of minutes during multi-potential steps, and revealed asymmetry of the relaxation time to the potential step direction [1]. In the present study, electrochemical reactions at the IL|Au interface have been studied using ESPR.
We have found that redox reactions at the IL|Au interface can also be sensitively probed using ESPR when we add redox species such as ferrocene and its derivatives in ILs. Sigmoid curves of the SPR angle are observed during electrode potential scan. We have analyzed the sigmoid curves by simultaneously using a theory and a digital simulation, and have revealed specific interaction between redox species and IL ions depending on their charges.
[1] N. Nishi, Y. Hirano, T. Motokawa, T. Kakiuchi, Phys. Chem. Chem. Phys. 15 (2013) 11615.