bluuebunny/crossref_metadata_2025 huggingface dataset:
Lithium Dendrite Suppressing Effect of Fluoroethylene Carbonate Additive on Surface Patterned Lithium Metal
Authors: Lee Hoogil , Han Taeyeong , Jin Dahee , Lee Yong Min , Ryou Myung-Hyun
Published: February 2020

Abstract

Due to the highest possible theoretical capacity (3860 mAh g-1 or 2060 mAh cm-3) and the lowest negative electrochemical potential (-3.04 V vs standard hydrogen electrode) lithium (Li) metal has been considered as the promising anode material for achieving a battery of high energy density. Nevertheless, the successful implementation of Li metal in the secondary battery system has been delayed due to the uncontrolled dendrite growth during repeated Li deposition/stripping process, resulting the capacity and safety degradation of battery system.

Recently, our group suggested to use the surface-patterned Li metal to suppress Li dendrite growth though a stamping technique [1-2]. We observed that the surface pattern was filled by granular forms of Li metal when the Li plating was conducted at a high current density condition. These can cause the consumption of large amount of Li ions to form solid electrolyte interface (SEI) on the newly exposed Li metal surface.

Herein, we investigated the Li dendrite impeding effect of FEC on the surface-patterned Li metal during the repeated Li plating processes at high current density. The effect of the FEC additive was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS).

Acknowledgements

This work was supported by the international Collaborative Energy Technology R&D Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea. (No. 20158510050020).

 

Reference

1. M.-H. Ryou, and Y. M. Lee, Y. Lee, M. Winter, P. Bieker, Advanced Functional Materials 2015, 25, 834-841

2. J. Park, J. Jeong, Y. Lee, M. Oh, M.-H. Ryou, and Y. M. Lee, Advanced Materials Interfaces 2016, 1600140
Enhanced High-Voltage Stability of LiNi0.6Co0.2Mn0.2O2 Cathode By Using Electrolyte Additive
Authors: Kim Jae-Hee , Pham Hieu Quang , Hwang Eui-Hyung , Kwon Young-Gil , Lee Jung-Gyu , Song Seung-Wan
Published: February 2020

Demands for high-power and high-energy Li-ion batteries are rapidly increasing for their use in electric vehicles. Nickel-rich three-components oxides of Li(Ni1-x-yCoxMny)O2 (NCM, 1-x-y ≥ 0.5) are one of the promising cathode active materials of high-energy density Li-ion batteries because of higher capacity, operation to higher charge cut-off voltage, lower cost and less toxicity than LiCoO2. However, their high-voltage performance is difficult to achieve due to limited anodic stability of conventional electrolyte above 4.2 V vs. Li/Li+. At such an aggressive charge condition, cathode-electrolyte interfacial reactions often cause a degradation of cathode material and electrolyte consumption by oxidative decomposition, resulting in a rapid performance fade.1-3 To stabilize the high-voltage interface between cathode and electrolyte, efforts such as surface coating of cathode materials with inorganic materials have been made.4 Recently, the use of high-voltage electrolyte additives 1-3 is recognized as efficient and economic, because they form a surface protective layer on the cathode, improve the interfacial stability and prevent further electrolyte decomposition. Here we report the development of a new electrolyte additive for cycling the LiNi0.6Co0.2Mn0.2O2 cathode to the charge cut-off voltage of 4.6 V. ex-situ X-ray photoelectron spectroscopic and Infrared spectroscopic studies on cathode-electrolyte interfacial reaction phenomena would be discussed in the meeting.

Acknowledgements

This research was supported by the Korean Ministry of Trade, Industry & Energy (A0022-00725 & R0004645) and Nano Material Technology Development Program through the National Research Foundation funded by the Ministry of Science, ICT and Future Planning (2009-0082580). 

References

1. Y. -M. Lee, K. -M. Nam, E. -H. Hwang, Y. -G. Kwon , S. -W. Song, J. Phys. Chem.
C, 118,10631 (2014).

2. D. T. Nguyen, J. Kang, K. -M. Nam, Y. Paik, S. -W. Song, J. Power Sources,
303,150 (2016).

3. H. Q. Pham, K. -M. Nam, E. -H. Hwang, Y. -G. Kwon, H. M. Jung, S. -W. Song, J. Electrochem. Soc.,
161, A2002 (2014).

4. Y. Chen, Y. Zhang, B. Chen, Z. Wang, C. Lu, J. Power Sources,
256, 20 (2014).
All Solid-State Lithium Cells Employing Hybrid Solid Electrolytes Containing Li+-Conducting Inorganic Electrolyte
Authors: Park Myungsoo , Jung Yun-Chae , Kim Dong-Won
Published: February 2020

Lithium-ion batteries have rapidly become the dominant power sources for portable electronic devices, electric vehicles and energy storage systems, due to their high energy density and long cycle life.1 However, safety issues still prevent full utilization of these batteries owing to the use of flammable liquid electrolytes, and thus safety problems have become a significant concern especially in large capacity applications such as electric vehicles and energy storage systems. In this respect, the development of all solid-state lithium batteries with non-flammable solid electrolytes may provide a fundamental solution to the safety issue of lithium batteries.2 As solid electrolytes, inorganic electrolytes have been actively studied for solid-state lithium battery applications. They usually exhibit relatively high ionic conductivity, wide electrochemical stability window and good chemical stability in contact with lithium metal. However, their hard and brittle mechanical properties do not allow easy construction of large-scale lithium batteries. In addition, lack of flexibility results in high interfacial resistance and poor interfacial contacts with electrode materials. Therefore, developing the flexible hybrid solid electrolyte with high ionic conductivity is an attractive and urgent work for all solid-state lithium batteries. In this study, the hybrid solid electrolytes composed of Li+-ion conducting inorganic electrolyte and polymer electrolyte were prepared in the form of flexible thin film, and their electrochemical properties were investigated. The hybrid solid electrolytes were applied to the all solid-state Li/LiNi0.6Co0.2Mn0.2O2cells, and their electrochemical performance was evaluated.

 

References

1. J.M. Tarascon and M. Armand, Nature, 414, 359 (2001).

2. E. Quartarone and P. Mustarelli, Chem. Soc. Rev., 40, 2525 (2011).
Novel Carbonate-Based Electrolyte Additive for High Voltage Lithium-Ion Batteries
Authors: Schroeder Marshall A , Cresce Arthur v. , Russell Selena M , Xu Kang
Published: February 2020

Harnessing the improvements in energy and power offered by high voltage (~5V vs. Li) lithium-ion electrode chemistries relies on development of more robust electrolytes with expanded stability windows. While some success has been demonstrated with incorporation of new solvents/co-solvents with enhanced intrinsic stability, adopting changes of this magnitude to established materials/methods at the industry level is a costly and cumbersome solution. One of the most appealing and affordable alternative approaches utilizes low fraction additives designed to favorably modify interface chemistry in order to stabilize cycling performance and mitigate parasitic reactions. In this work, we synthesize a new additive chemistry and demonstrate its utility in improving cycling performance and limiting parasitic currents, even at high operating voltages (up to 5.5V vs. Li), as compared to baseline electrolytes in Li/LiNi1.5Mn0.5O4 half cells. Quantum chemical modeling and interphase characterization provide some insight with regard to the mechanism for enhanced stability.
(Invited) Development of Transformational Technologies
Authors: Soloveichik Grigorii L.
Published: February 2020

The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical energy storage and transformation for grid scale and automotive applications.

Storing energy in the form of liquid fuels has numerous advantages compared to conventional methods of energy storage (ES) such as batteries (high cost, short cycle life), pumped hydro and compressed air (low energy density). Low costs of storage and transportation of liquid fuels enables long-time ES and effective energy transportation using existing infrastructure technologies. Electrochemical synthesis of fuels allows for direct conversion of renewable electricity to chemical energy, which simplifies the process and increases the process efficiency. ARPA-E funds several projects targeting electrochemical synthesis of liquid fuels via OPEN and focused programs. The Reliable Electricity Based on Electrochemical Systems (REBELS) program aiming at distributed generation for more reliable and flexible smart grid focuses on intermediate temperature fuel cells that operate between 200-500oC and includes cell capable to produce liquid fuels along with electricity. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program seeks to fund the development of transformational technologies to reduce the barriers to widespread adoption of intermittent renewable energy sources by enabling the conversion of energy from these sources, water and air to energy-dense zero-carbon liquid fuels. This presentation will also highlight flow battery technologies using organic active materials including funded by ARPA-E. A comparison of organic and inorganic active materials in aqueous and non-aqueous electrolytes for flow battery applications will be presented. Compatibility of fuels, electrocatalysts and membranes will be discussed. State-of-the-art technologies for electrochemical synthesis of fuels and organic active materials using different types of electrochemical cells will be presented.
(Invited) Electrochemical and Photoelectrochemical Reduction of Carbon Dioxide: The Twain Shall Meet at Copper Oxide/Copper Nanocube/Liquid Interfaces
Authors: Rajeshwar Krishnan
Published: February 2020

Of the myriad electrode materials that have been used for the electrochemical (EC) and photoelectrochemical (PEC) reduction of carbon dioxide in aqueous media, copper oxide/copper interfaces have shown a remarkable range of hydrocarbon and oxygenated products including acids, aldehydes, ketones, and alcohols. This talk highlights experimental evidence for the fact that both EC and PEC reduction scenarios have similar morphological underpinnings in the in situ formation of copper nanocubes on the (photo)cathode surface. Recent rapid developments in our fundamental understanding of these interfaces and areas requiring further studies are discussed in the light of recent studies in the authors’ laboratories and elsewhere.
(Invited) Electrocatalysis of CO2 Reduction. from Fundamental Understanding to Catalyst Design and Preparation
Authors: Tian Na , Sheng Tian , Liu Li , Xie Ai-Yun , Zhang Feng-Yang , Hong Yu-Hao , Huang Long , Zhou Zhi-You , Sun Shi-Gang
Published: February 2020

Electrocatalytic reduction of CO2 is of significance in environment for reducing greenhouse gas level, in carbon recycling and sustainable energy storage when CO2 is reduced into hydrocarbon fuels and other chemicals. The big challenge in electrocatalysis of CO2 reduction consists in the high energy barrier to activate the O=C=O band and the broad distribution of products. Therefore, the key issue is design and preparation of electrocatalysts with high catalytic activity and selectivity. In recent years, we have conducted investigations of electrocatalysis of CO2 reduction in the following three aspects:

(1) Using Pt single crystal planes (Pt(hkl)) as model catalysts to gain knowledge about the surface structure-catalytic functionality of CO2 reduction. In situ FTIR spectroscopy determined that the main CO2 reduction product on Pt(hkl) electrodes is CO, while the kinetics of the CO2 reduction depends on the surface atomic arrangements. It has revealed that the catalytic active centers for CO2 reduction consist of few atoms (5-6) of low coordination number (steps, kinks) in stereo structure;

(2) Investigation of electrocatalytic reduction of CO2 on a series Cu-based electrodes, including Cu tetrahexahedral nanocrystals bounded by {530} high-index facets prepared through electrochemically shape-controlled synthesis, polycrystalline Cu and oxide-derived Cu electrodes decorated with Zn, Ni and Au. The CO2 reduction products were determined by using mainly NMR. It has found that the decoration of Ni on oxide-derived Cu exhibited the highest catalytic activity for CO2 reduction, evidenced by significant increase in Faraday efficiency for yielding formic acid, ethanol, and n-propanol. At -1.5 V, the Faraday efficiency are respectively 30%, 1.6% and 2.7% for formic acid, ethanol and n-propanol on Ni decorated oxide-derived Cu, while the values are 8.3%, 1.2%, and 1.6% on Zn modified surface, 20.5%, 0.2%, and 0% on Au modified surface, and 20.9%, 0.8%, and 1.0% on the bare oxide-derived Cu surface. The promotion may mainly come from the stronger adsorption of intermediate CO* on Ni decorated surface than on Cu, which facilitates further the reduction of CO* with optimized hydrogen adsorption on Ni;

(3) DFT calculations of electrocatalytic reduction of CO2 through the development of methods for accurately modelling the electrochemical interface by using a liquid water/solid interface model with a number of explicit water molecules combining with ab initio molecular dynamics simulations. In this study, Cu(100) was used as model catalyst, the results revealed different intermediates and pathways involved in CO2 reduction and provided a detail description of the reaction mechanism and kinetics.

Acknowledgements: The study was supported by NSFC (21573183, 21229301, 21321062).
Understanding Selectivity of Carbon Dioxide Reduction to Carbon Monoxide and Formic Acid on Sn Electrodes
Authors: Feaster Jeremy T , Shi Chuan , Cave Etosha , Hatsukade Toru , Abram David N , Hahn Christopher , Kuhl Kendra , Nørskov Jens , Jaramillo Thomas F
Published: February 2020

Increases in energy demand and chemical production, together with the rise in CO2 levels in the atmosphere require new, renewable energy sources to be developed. Electrochemical CO2 reduction to fuels and chemicals is an appealing alternative to traditional methods of producing energy and chemicals due to its simplicity and ability to implement with solar and wind energy sources. Sn has been identified as a promising catalyst for the CO2 reduction reaction (CO2RR) to formate (HCOO-), a key chemical for many industries; however, there is a lack of experimental data to corroborate the prevailing theories of the mechanism and key intermediates for HCOO- production. This work reports a joint experimental and theoretical investigation of the electrochemical reduction of CO2 on polycrystalline Sn surfaces. Our results show that Sn electrodes produce HCOO-, carbon monoxide (CO) and hydrogen (H2) across a range of potentials, and that HCOO- production becomes favored after -0.8V vs. RHE, reaching a maximum faradaic efficiency of 70%. Scaling relations for Sn and other transition metals are examined using experimental current densities and density functional theory (DFT) binding energies. While *COOH was determined to be the key intermediate for CO production on metal surfaces, we suggest that it is unlikely to be the primary intermediate for HCOO- production. Instead, a strong correlation between *OCHO and HCOO- production is observed, suggesting that the key intermediate for the CO2RR to HCOO-. Sn’s optimal *OCHO binding energy explains its high selectivity for HCOO-. These results suggest that oxygen bound intermediates are critical to understand the mechanism of CO2 reduction to HCOO- on metal surfaces.
Key Parameters for the Design of Composites Electrodes for Water Splitting in Alkaline Medium
Authors: Arcidiacono Paul , Favier Frederic
Published: February 2020

A study on the hydrogen evolution performances in alkaline medium (KOH 6M) of nickel-based composite electrodes has been carried out. Surface tension characteristics have been tuned by using various polymer binders of different hydrophobic/hydrophilic balances: polyvinyl alcohol (PVOH), polybenzimidazole (PBI), polyethylene oxide (PBI), polyvinidylene fluoride (PVDF), and Polytetrafluoroethylene (PTFE).

The composite electrodes fabricated by drop-casting exhibit various contact angles in an extended range from 43° to 115°. They were evaluated by steady-state polarization and electrochemical impedance spectroscopy (EIS) measurements. Electrochemical behavior and mechanism were discussed towards the electrode wettability through the evaluation of electrochemical parameters including the overpotential at 100 mA/cm², kinetic parameter b (mV/dec) and charge transfer resistance (Rct).

The bubble coverage, diameter before departure (lift off from the electrode surface) and residence time at the surface are greatly affected by the surface tension of the various electrodes. The comparison of the electrochemical performances revealed the importance of this characteristic for the design of an efficient hydrogen evolution electrode fabricated by a catalyst-binder approach.

From Ni-PVOH to Ni-PTFE electrodes with the same catalyst loading, the overpotential at 100 mA/cm² was improved by 150 mV. The kinetic tafel slope was kept close to 116 mV/dec (Volmer-Heyvroski step) for electrodes with a contact angle between 43° to 90 °, increased for contact angles above 90° to reach up to 178 mV/dec for PTFE-based electrode showing the greater contact angle in the series at 115°. Electrochemical impedance spectroscopy (EIS) measurements at various overpotentials show that the bubbles retained at the surface increase the electrode charge transfer resistance. This behavior is assigned to the hidden active sites and justifies the observed decrease in performances of hydrophobic electrodes.

This comprehensive study leads to a precise description of the interfacial phenomena at the microscopic scale during gas production by electrolysis and the evaluation of key parameters for the formulation of advanced electrodes.
Self-Supported Nickel Phosphide Nanoparticles with High Activity for Hyderogen Evolution Reacition
Authors: Jang Injoon , Park Hyun-Seo , Kim Jin Young , Jang Jong Hyun , Kim Hyoung-Juhn , Sung Yung-Eun , Yoo Sung Jong
Published: February 2020

Hydrogen (H2) production have received considerable attention resulting from the urgent need of clean and renewable energy. Water splitting is a typical and eco-friendly strategy for H2 production method through efficient acidic electrolyzers with expensive platinum group metal catalysts (Pt). Therefore, researchers have developed alternative, cheap and robust catalysts made from earth-abundant elements. Very recently, nickel phosphides (NixPy) have been proven to be promising catalysts with high activity and durability in strong acidic media (0.5M or 1M H2SO4) for hydrogen evolution reaction (HER). The crystalline phase of NixPy is an important factor for determining the activity for HER (better HER activity as higher P contents in NixPy).

Herein, highly active and durable NixPy catalysts for HER are prepared using modified thermal decomposition method. In this process, nickel oxide (NiO) powder reduced to NixPy by phosphine gas (PH3) produced from sodium hypophosphite (NaH2PO2). Unlike conventional method, NiO is phosphidized from bi-located P source (NaH2PO2). One is placed upstream of furnace (traditional method) and the other is mechanically mixed with NiO powder. Based on X-ray diffraction analysis, synthesized NixPy catalysts had multi-phase crystalline structure (Ni2P, Ni5P4 and NiP2) and the NixPy with higher P content exhibited the smaller crystallite size. (Ni2P < 50 nm, Ni5P4 ~ 10 nm, NiP2 ~ 2nm). Consequently, Ni5P4 and NiP2 nanoparticles with higher HER activity are supported on micro-scaled Ni2P with better conductivity (self-supported NixPy nanoparticles), which result in improvement of electrochemical properties for HER. The NixPy catalysts showed exceptionally higher HER activity and durability in acidic media than single-phased Ni2P or Ni5P4 and this performance of the NixPy is comparable with that of Pt. Therefore, modified phosphidation method and self-supported NixPy catalyst provide new instruction for designing excellent HER catalysts.
Development of Intermediate Termperature Fuel Cells for Direct Conversion of Methane to Liquid Fuels
Authors: Willman Carl A. , Barton Joseph , Ghezel-Ayagh Hossein , Torabi Alireza , Maric Radenka , Poozhikunnath Abhinav , Li Na , Marina Olga A , Nguyen Hoang V. P. , Mitroshkov Alex , Zhong Lirong , Polikarpov Evgueni , Pederson Larry
Published: February 2020

An electrochemical route to upgrade methane to liquid products, such as methane is being investigated. The process is based on an oxide conducting electrolyte and a metal/metal oxide redox couple, to partially oxidize methane to oxygenates. The objective of this project is development of a durable, low-cost, and high performance Low Temperature Solid Oxide Fuel Cell (LT-SOFC) for direct conversion of methane to methanol and other liquids, characterized by: a) operating temperature < 500°C, b) current density of > 100 mA/cm2 in liquid hydrocarbon production mode, c) continuous operation of > 100 h, d) cell area > 100 cm2, e) cell cost per rate of product output < $100,000/bpd, f) process intensity of > 0.1 bpd/ft3, g) product yield and carbon efficiency > 50%, and h) volumetric output per cell > 30 L/day.
(Invited) Molecular Mechanisms of Oxygen Evolution and Water Splitting at Elevated Temperatures
Authors: Chueh William C
Published: February 2020

High-temperature electrolysis employing oxygen-ion-conducting solid electrolytes is a promising method to synthesize fuel. However, the molecular reaction mechanisms at the gas/electrode interface is not well-understood. In recent years, a variety of in-situ characterizations and density-functional theory calculations have elucidated the reaction mechanisms. In this talk, I will present a comprehensive understanding of oxygen-evolution and water-splitting reactions on perovskite and fluorite oxides at the molecular level.
(Invited) High-Temperature Electrosynthesis of Hydrogen and Chemicals
Authors: Minh Nguyen , de Miranda Paulo Emilio V.
Published: February 2020

High-temperature electrochemical cells based on solid electrolytes have been considered for synthesis and production of hydrogen and a variety of other fuels and chemicals. Solid oxide electrolysis cells (SOECs), for example, are being developed for hydrogen production (from water), syngas production (from mixtures of water and carbon dioxide) and oxygen recovery (from water or carbon dioxide for space applications). The main attractive features of the SOEC are its simple chemistry, environmental compatibility and high electrical-to-hydrogen efficiency. Solid oxide fuel cell (SOFC) type cells have been investigated for production of chemicals and cogeneration of electricity and chemicals (in this case, the cell is referred to as CSOFC); examples include production of C2 hydrocarbons and syngas from methane. The key features of the CSOFC include its high selectivity and the possibility to produce valuable chemicals such as hydrocarbons using methane-rich gases from non-fossil origins. Current state-of-the-art SOECs and CSOFCs, both fundamentally derived from the more advanced conventional SOFC technology, are still in their feasibility/development stage. This paper discusses certain aspects in selected materials, performance and operation of the SOEC for hydrogen production from water and the CSOFC for production of C2 hydrocarbons from methane.
(Invited) Synthesis and Upgrading of Fuels Using Solid State Electrochemical Devices
Authors: Elangovan S , Hartvigsen Joseph J , Larsen Dennis , Hafen Tyler , Mosby James M , Elwell Jessica , Frost Lyman J
Published: February 2020

High conversion efficiency and selectivity are the two primary attractive features of electrochemical processes, in particular those using high temperature ion selective membranes. By selectively removing specific ionic species, the radicals that are created will react to form new compounds. Oxygen ion conductors are commonly used to remove oxygen from oxidized species thus creating molecules with fuel value. Judicious selection of materials set and device operating conditions are required to achieve desired product formation. The electrocatalytic layers on the electrochemical cells perform two functions, that of a catalyst and as an electrical conductor. Appropriate choice of electrode materials is required for stable performance and to avoid unwanted product formation. Control of operating conditions, namely temperature, fraction converted, and driving potential also is critical to achieve the selectivity.

Ceramatec is currently developing electrochemical technologies using zirconia membrane based electrolysis devices for multiple applications. One is the production of fuels such as hydrogen from steam and syngas from a mixture of steam and carbon dioxide. The product can be used as gaseous fuel or further converted to liquid fuels using conventional chemical processes. The process enables highly efficient conversion and storage of intermittent wind and solar energy in the form of energy dense liquid fuels. The second application involves electrolysis of carbon dioxide of Mars atmosphere to produce CO and oxygen for fuel synthesis and life support for future manned mission. A third application is to develop deoxygenation technology to remove oxygen from liquid hydrocarbon compounds produced from biomass to increase its fuel properties.

The requirements of each of these applications are varied and necessitate different operating conditions and significant changes to conventional electrode materials developed for high temperature fuel cell applications. An overview of these technical challenges and approach to addressing them will be presented.
(Invited) Luminescence of Lanthanide-Doped Nanocrystals
Authors: Meijerink Andries
Published: February 2020

Nanocrystals (NCs) doped with luminescent ions form an emerging class of materials. They serve as probes in physics, chemistry and biology and demonstrate unprecedented flexibility in spectral conversion (including up- and downconversion) for applications ranging from solar cells and white light LEDs to photodynamic therapy. In this presentation the synthesis and optical properties of lanthanide doped nanocrystals (both quantum dots and insulator nanocrystals) will be discussed with a focus on design strategies to tailor the luminescence properties and to enhance spectral conversion efficiencies.
(Invited) Considerations of LED Efficiency for the Development of Phosphors for Solid State Lighting
Authors: Piquette Alan , Mishra Kailash C. , Bergbauer Werner , Galler Bastian
Published: February 2020

The efficiencies as well as other spectral properties of near-UV, violet or blue light emitting diodes (LEDs) are too critical to be neglected when designing phosphors for white light emission in solid state lighting.

The efficiency, in particular, limits which phosphors are appropriate and which mechanisms should be explored further.  In this talk, we will present efficiency data from state-of-the-art LEDs (Figure 1) and discuss their implications for phosphor design.

Given the spectral variations of LED efficiencies shown in Figure 1, we will consider limitations imposed on luminescence mechanisms such as absorption and emission processes, Stokes shift, and radiative lifetime, and high flux operations.  Specifically, we will compare f→f, f→d, and d→d absorption mechanisms and use arguments based on oscillator strength to demonstrate why phosphors that rely on f→f absorption may not be good options. Stokes losses are unavoidable for any phosphor, but need to be minimized for overall energy efficiency. At the same time, designing a blue phosphor for either near-UV or violet LEDs is rather too difficult because of the required small Stokes shift for a broadband phosphor. Even if an efficient blue phosphor could be found, its emission is re-absorbed by the green and red components leading to lower efficacies.  Another important consideration is the flux level encountered by the phosphor layer in LEDs. For a 1 mm2 LED operating at 35 A/cm2, the irradiance for a chip-level-converter is on the order of 0.5 W/mm2 (assuming a 1 W chip with 50% energy efficiency). This is significantly higher than traditional fluorescent technology where the irradiance is ∼10−4 W/mm2 for a typical T8, 4 ft. lamp operating at 50 kHz.[1]At such high flux densities, a phosphor needs to have either a short radiative lifetime or it must be removed from the chip and used in a remote configuration in order to avoid ground state depletion. With laser-activated phosphors becoming more popular, these lifetime considerations will become even more crucial.

We will also discuss the need for narrowband red phosphors and briefly evaluate the known options such as f→f transitions from trivalent lanthanides, d→d transitions from Mn4+ or Cr3+, and relatively narrow band emission due to d→f transitions from Eu2+in some nitride hosts, and, of course, quantum dots.

Finally, simulations comparing the spectral efficiencies and color rendering quality of both near-UV and blue pumped white light sources will be presented. Optimal choices for spectral properties of phosphors as well as LEDs will be discussed.

[1] A. Piquette, W. Bergbauer, B. Galler, and K. C. Mishra, ECS J. Solid State Sci. Technol., 5, R3146 (2016).

Figure 1
UV-Blue Emitting SiO2 Sintered Glass for Radiation Dosimetry
Authors: Okada Go , Kawaguchi Noriaki , Yanagida Takayuki
Published: February 2020

Phosphor materials are often used in radiation measurement as a converter, from ionizing radiation to light. In dosimetry, a phosphor material absorbs and accumulates the incident radiation energy over a certain period of time as electronic charges trapped at localized centres. A recombination of these charges can be stimulated externally by light exposure or heat, followed by light emission. The latter emission intensity is proportional to the incident radiation dose accumulated, hence the radiation dose can be indirectly measured. Today, such phosphor materials are used in a variety of scenes, for example, personnel dose monitoring, radiation therapy, and medical imaging.

In this study, we have synthesized bulk SiO2 glasses and characterized for dosimetry applications. The samples were prepared by spark plasma sintering (SPS), which is a unique way to obtain a bulk SiO2 glass. First, radioluminescence (RL) spectrum was measured for both the prepared sample and SiO2 single crystal. The glass sample showed a broad emission feature from 300 to 500 nm while the crystal sample showed a narrower emission around 450 nm. The RL measurement at low temperatures revealed that the broad emission by glass consists of two components with the peaks at 385 nm and 511 nm. The origin of the former emission seems to be a pair of silylene centres generated by sintering process while the latter is due to a presence of dioxasilirane and sililene. Moreover, it was found that the sample shows a strong thermally-stimulated luminescence (TSL) after X-ray irradiation. The glow curve indicates strong emissions at the temperatures of approximately 140 °C and higher than 300 °C. In contrast, SiO2 single crystal shows much weaker signal at lower temperature (~90 °C). The luminescent centres responsible for TSL are the silylene-silylene pair emitting at 385 nm. With a use of TSL in our SiO2 glass sample, a detectable X-ray dose range is at least 1 - 10000 mGy, which is a comparable sensitivity to commercial dosimeter.
Scintillation and Dosimeter Properties of MgO Transparent Ceramic Doped with C
Authors: Kato Takumi , Okada Go , Yanagida Takayuki
Published: February 2020

From the view point of MgO for radiation detector uses, in the 1970s, undoped MgO powder was found to show dosimeter properties. When it was irradiated by X-ray, γ-ray and UV, two TSL glow peaks were found around 90-100 and 140 °C [1]. Furthermore, in the later decades, MgO have been intensively studied for dosimeter applications due to the bioequivalency [2].

In this study, we synthesized a series of transparent ceramic MgO doped with 0.001, 0.01 and 0.1% of C by a Spark Plasma Sintering (SPS) method and studied scintillation and dosimeter properties against X-rays. The C-doping is inspired by C-doped Al2O3crystalline powder used for a personal dosimeter [3]. Recently, it was pointed out that scintillation and dosimeter are complementarily related in some material systems [4] so investigations of both the dosimeter and scintillation properties are important to understand the luminescence phenomena induced by ionizing radiations.

In the scintillation spectra, the emission bands were detected around 400 and 760 nm, and the origins of these peaks were assigned in previous reports [5]; therefore, we think that emission peaks around 400 and 760 nm may be due to F+ center and Cr3+ ion impurity, respectively. Moreover, the emission peak was also observed at 330 nm and it is said that its origin related to surface (grain boundary) defect [6]. Compared with the scintillation spectrum of the undoped MgO transparent ceramic in Ref [5], 330 and 400 nm peak intensities increased while 750 nm peak intensity decreased with C-doping. This result suggests two possibilities; a first one is that electrons are hard to transport to Cr3+ ion because C-doping generated F+ center and surface defect acting as emission center newly. The number of generated careers are finite, and if most careers recombine at these defect emission centers, Cr3+emission should be reduced. A second one is that defects generated by C-doping simply act as trapping centers, and in this case, careers would be stored.

 

H. Nanto, K. Inabe, H. Yamazaki and N. Takeuchi, J. Phys. Chem. Solid.,
36 477 (1975).

C. Soliman, Radiat. Eff. Defect. S., 164 257 (2009).

S.W.S. McKeever, Radiat. Meas., 46 1336 (2011).

T. Yanagida, J. Lumin., 169 544 (2016).

T. Kato, G. Okada, T. Yanagida, Ceram. Int., 42 5617 (2016).

F. Gu, et al., J. Alloy. Compd., 453 361 (2008)
Thermal Neutron Response of Tungsten Doped Lithium Fluoride Single Crystal
Authors: Kawaguchi Noriaki , Okada Go , Yanagida Takayuki
Published: February 2020

The He-3 supply crisis have currently caused demand of alternative neutron detectors of He-3 gas filled proportional counters. One of the alternative detectors is a scintillation counter which consists of a solid neutron scintillator and a photodetector such as a photomultiplier tube (PMT). The LiF:W single crystal is known as a scintillation material and contains Li-6 which convert thermal neutrons into high energy charged particles. However, neutron scintillation properties of LiF:W were not clear because there were no comparative studies with other traditional neutron scintillators.

 In this study, photo-luminescence (PL) properties, X-ray excited radio-luminescence (XRL) properties and pulse height spectra under thermal neutron irradiation of LiF:W single crystal (diameter, 25.4 mm; thickness, 25.4 mm) were evaluated. At the same time, ones of Li-glass scintillator were also measured as a reference. From PL spectra under 250 nm UV light excitation and XRL spectra, emission peaks of LiF:W and Li-glass were observed at around 440 nm and 400 nm, respectively. Bialkali PMTs are sensitive to these wavelengths. PL quantum yields of LiF:W and Li-glass were 25.8% (under 250 nm UV light excitation) and 80.1% (under 340 nm UV light excitation), respectively. PL and XRL decay curves of LiF:W were also measured and both decay times were several tens of micro second. On the other hand, decay time of Li-glass is reported less than 100 ns. As a result of evaluation of pulse height spectra of LiF:W and Li-glass under thermal neutron irradiation, thermal neutron events were successfully observed by using both materials. In case of using LiF:W, we obtained a broad detection peak around the thermal noise level of PMT. This result will be explained with low PL quantum yields and slow decay time of LiF:W.
A Study on Synthesis of SrLu2O4:Eu2+ Red Phosphor and Its Photoluminescence Properties
Authors: Kim Kyeong-Ho , Kang Eun-Hee , Hong Seong-Hyeon
Published: February 2020

During the last decades, rare-earth (RE) ion-doped phosphors have received much attention due to their high luminescent properties. For this reason, many studies have been focused on new composition of phosphor with high luminescent properties. Eu3+ doped SrLu2O4, which is a new composition phosphor, has been reported to describe the luminescent properties. Upon excitation with ultraviolet (UV) regions, Eu3+ doped SrLu2O4 phosphor exhibited narrow red emissions due to the 4f-4f transition of Eu3+ ions. Eu3+ ions only can be excited with UV regions and the property of narrow red emission has a limitation to apply for lighting devices such as white light-emitting diodes (WLEDs) due to a low color rendering index (CRI).

In this study, we synthesize the Eu2+ doped SrLu2O4
red phosphors with solid-state reaction and characterize the luminescent properties for the first time. For the synthesis of SrLu2O4 at stoichiometric condition, it is hard to synthesize the pure SrLu2O4 phase, because formation of a second phase Lu2O3 were consistently unable to avoid. The pure phase of SrLu2O4 was formed at certain ratio of starting materials and annealing temperature conditions. The mixtures were annealed at various temperatures (1400–1600 °C) for 3 hours under 5% H2/N2 atmosphere in order to reduce Eu3+ to Eu2+.

Upon excitation with 450 nm, the synthesized SrLu2O4:Eu2+ phosphors exhibited a strong red emission centered at 610 nm due to the 4f-5d transition of Eu2+ ions (Figure 1). SrLu2O4:Eu2+ phosphors showed highest PL intensity at very low europium doping level, which intensity value was 85% of commercial (Sr,Ca)AlSiN3:Eu2+ (SCASN). In addition, SrLu2O4:Eu2+ phosphors also showed a strong thermal quenching property, which indicated that PL intensity measured at 200 oC was reduced to almost zero per cent of the initial value (25 oC). These high value of PL intensity and strong thermal quenching property can be used as a high potential optical temperature sensor application.

Figure 1
Relationship Between, the Centroid Shift of Eu2+ and Ce3+ with the Band Gap of the Host Lattice
Authors: Camardello Sam Jospeh , Srivastava Alok M , Toscano Paul J , Setlur Anant A
Published: February 2020

In this the talk the relationship between the centroid shift of Ce3+ and Eu2+ and the host lattice exciton energy is discussed. Combining this relationship with the dependence of the crystal field splitting on the coordination polyhedral [1] can define the excitation spectra of Ce3+ and Eu2+ in a given host lattice.

Figure 1: The Centroid shift vs. the host lattice exciton energy for Ce3+ and Eu2+

[1] P. Dorenbos, J. Phys.: Condens. Matter, 15, 4797 (2003).

Figure 1
Photoluminescence Properties and Energy Transfer in Color-Tunable Garnet Phosphor for High Quality LED Lighting
Authors: Won Seob , Arunkumar Paulraj , Im Won Bin
Published: February 2020

Recently, the performance of phosphor-converted white light-emitting diodes (WLED) has been improved mainly by diversifying the components, encapsulation of the device, phosphor synthesis, as well as designing new strategies for the development of phosphors. Nowadays, single-composition white-emitting phosphors which are excited by near UV or blue LED have been developed to prevent the reabsorption, instability of color temperature, and cost issues.

We report a garnet phosphor with partially displaced Tb3+ and Pr3+ as green and red components respectively. A green-emitting and white-emitting phosphor was synthesized by a solid-state reaction, exhibiting an efficient green emission and red emission at 543 nm and 609 nm under blue excitation. The structural and optical properties of the phosphor were studied using powder X-ray diffraction and photoluminescence analysis. The compound crystalizes in cubic phase with space group Ia
d. The partial substitution of Tb3+ and Pr3+ in garnet phosphor led to a considerably broad emission spectrum. The WLED was fabricated by using phosphor-in-glass with a blue LED chip and exhibited a warm white light with an excellent color rendering index of 92. The garnet phosphor with Ce3+, Tb3+, and Pr3+ is thus a potential green and white-emitting phosphor for LED lighting.

Figure 1. PL excitation and emission spectrum of garnet phosphor with (a) Ce3+, (b) Ce3+, Tb3+, and (c) Ce3+, Pr3+.

Figure 1
Synthesis of New Melilite Structured Blue Phosphor for UV LED
Authors: Kim Ha Jun , Im Won Bin
Published: February 2020

Solid-state LED lighting has been in the spotlight due to its high efficient, energy savings, and eco-friendly nature. Conventional blue LED based white lighting in combination with yellow phosphors showed high luminous efficiency (>30 lm/W) but have serious issue of poor color rendering index (65) due to weak red emission. As an alternative, UV based white LEDs has been under intensive research due to its high color rendering index (99), excellent conversion efficiency and a wide emission band ranging 350 to 700 nm.

In this study, a blue-emitting melilite phosphor was developed with wide absorption in the near-UV by solid-solution. The synthesized blue phosphor has wide absorption band with a maxima at 420 nm. The emission wavelength was tunable in the window of 470 to 505 nm. The structural and optical characteristics were investigated using X-ray diffraction, Rietveld refinement, photoluminescence, thermal quenching and decay time. Finally white LED was fabricated using the optimized melilite blue phosphor in combination with commercial green and red phosphor under 420 nm LED chip. The results indicate melilite blue phosphor could be promising blue component for UV based white LEDs.

Fig1. Normalized excitation and emission spectra of the Sr4-x-y
Ca
­x
Ba
y
MgAl2Si3O14:Eu2+

Figure 1
(Invited) Discovery and Structural Design of New LEDs Phosphors
Authors: Xia Zhiguo
Published: February 2020

Phosphor materials enable the wavelength conversion to realize the full-color white emission light-emitting diodes (LEDs). So far much effort has been devoted to the design and discovery of novel LED phosphors for solid state lighting. Understanding and exploring the structural design principles of the inorganic hosts are necessary for the discovery of novel LED phosphors. Our recent work focuses on the discovery of new phosphor materials based on the structural evolution and the crystallographci sites engineering. Firstly, photoluminescence tuning can be realized via the cation substitution on one site, and hereby we have discovered several types of M2SiO4-based and M3(PO4)2-based phosphors with tunable emission for white LEDs.1-2 Secondly, we have recently proposed the concept of “chemical unit cosubstitution” as one potential design scheme, and the chemical unit cosubstitution strategy is applied to the melilite structure class designing the Ca2(Al1−x
Mg
x
)(Al1−x
Si1+x
)O7:Eu2+ solid solution phosphor via the [Mg2+−Si4+] for [Al3+−Al3+] cosubstitution.3 We also design the La5Si3O12N phase from La5Si2BO13 via the [B3+−O2−] by the [Si4+−N3−] cosubstitution.4 Thirdly, we have proposed a new insight into the design of the isostructural phases via the filling of M+ in the void channels of the Mg2Al4Si5O18 phase, so that the charge balance can be kept while the chemical composition varied, and this strategy will be also efficient in other porous inorganic hosts.5 Finally, we have recently studied the NaScSi2O6-based phosphor from CaMgSi2O6-based phosphor via the chemical unit cosubstitution of [Na+–Sc3+] for [Ca2+-Mg2+] unit.6 Further studies show that the isostructural solid-solution of (CaMg)
x
(NaSc)1-x
Si2O6 (0 < x < 1) can be formed, in which cation nanosegregation enables the presence of dilute Eu2+ at two centers and their intensities are linearly proportional to x, so that it represents a new cation nanosegregation tuning of photoluminescence for the exploration of color-tunable phosphor for white LEDs.7-8

References

[1] Z. G. Xia*, et. al., Inorganic Chemistry, 2015, 54, 7684-7691. (Cover paper)

[2] Z. G. Xia*, et. al., Journal of Physical Chemistry C, 2015, 119, 2038–2045.

[3] Z. G. Xia*, et. al., Journal of the American Chemical Society, 2015, 137, 12494-12497.

[4] Z. G. Xia*, et. al., Journal of Physical Chemistry C, 2015, 119, 9488–9495.

[5] Z. G. Xia*, et. al., Scientific Reports, 2015, 5, 12149.

[6] Z. G. Xia*, et. al., Journal of Physical Chemistry C, 2013, 117, 20847−20854. (Cover Paper)

[7] Z. G. Xia*, et. al., Scientific Reports, 2013, 3, 3310-3310-7.

[8] Z. G. Xia*, et. al. Journal of the American Chemical Society, 2016, 138, 1158-1161.
(Invited) Investigation of Blue Excitation Flux Dependent Conversion Efficiency in Phosphors for High Luminance Applications
Authors: Raukas Madis , Avallon James , Kelso John , Lenef Alan , Wang Jingzhou
Published: February 2020

Solid State Lighting (SSL) devices based on phosphor conversion have significantly evolved on a scale of output flux and white light luminance and extend now to the range where competition with the brightest arc discharge-based sources is ongoing. Such sources are unique in the SSL world in that they provide both an expanded emission spectrum and high luminance. The efficiency of high luminance semiconductor pumped phosphor sources depends not only on efficient generation of primary radiation from the semiconductor (LEDs or laser diode), but also strongly on the conversion material which is being pushed to optical and thermal limits. Such conversion materials are typically operating under heavy irradiance and thermal load and nearly always exhibit sublinear behavior in output at high input fluxes, due to a multitude of reasons. In the present study, we have separated contributions from thermal and non-thermal quenching mechanisms, in particular investigated phosphor saturation, or excitation quenching, in the converter light output as a function of blue pump intensity. It is important here to distinguish between the true loss mechanisms (for example via Auger-like or excited state absorption processes [1-6]) and the reduction in converted output due to increased transparency for the pump light (e.g. activator ground state depletion). We discuss the behavior of measured conversion efficiency as a function of excitation intensity (and parameters like temperature, activator type and concentration or host material). A model is proposed to explain the observed dependencies in different host-activator systems.

[1] W.J. Miniscalco et al, J.Appl.Phys., 49, 6109 (1978)

[2] D.S. Hamilton et al, Phys.Rev.B 39(13), 8807 (1989)

[3] K. Wisniewski et al, Acta Phys. Polonica A, 95(3), 403 (1999)

[4] K.C. Mishra et al, J.Electrochem.Soc. 151(5), H105 (2004)

[5] A. Lenef et al, SPIE 884107 (2013)

[6] O.B. Shchekin et al, Phys.Status Solidi RPL 1-5 (2016)