William A. Hollerman

Triboluminescent materials for smart sensors

Since the beginning of 21 st Century, scientists and engineers have been investigating triboluminescent materials for use in smart impact sensors. One of the brightest triboluminescent materials found thus far is europium dibenzoylmethide triethylammonium (EuD 4 TEA). This material was discovered by Hurt in 1966 and is bright enough to be seen in daylight. Through innovative design of the material synthesis steps and by exchanging europium chloride for europium nitrate, the triboluminescent emission was increased by over 80%. In addition, the material yield was increased, as chloride washing is not required. Here, we discuss the new synthesis process, triboluminescent results, and future applications of EuD 4 TEA phosphors.

Comparison of the triboluminescent properties for europium tetrakis and ZnS:Mn powders

In 2006, some authors determined that the triboluminescence (TL) of manganese-doped zinc sulfide (ZnS:Mn) increases with increasing impact velocity. In 2011, the authors discovered a method of synthesizing europium dibenzoylmethide triethylammonium (EuD4TEA) that produced TL 106% greater than ZnS:Mn. In fact, this material is bright enough to be seen in daylight. This paper investigates the effects of increasing impact energy on the TL of EuD4TEA and various grain sizes of ZnS:Mn using a drop tower. The low energy results indicate that increasing impact energy can increase the triboluminescent light yield for impact energies up to 1.4 J, the upper limit of the drop tower. The minimum activation energies required for each material are also explored. In addition, the effects of the increasing impact energy on the triboluminescent decay time are also investigated. The details of the experimental setup, synthesis of EuD4TEA, and results are discussed in this paper.

Comparison of the triboluminescent yield and decay time for europium dibenzoylmethide triethylammonium synthesized using different solvents

Europium dibenzoylmethide triethylammonium (EuD4TEA) is one of the brightest known triboluminescent (TL) materials. First synthesized in 1966, emission from EuD4TEA is bright enough to be seen in daylight. In this paper we report the synthesis of Eu(III) tetrakis compounds using different solvents, and their influence on the appearance, TL yield, and decay time. The physical appearance of Eu compounds changed with the solvent type. Further, the solvents influenced the time for nucleation and completion of the reaction. TL measurements show that Eu tetrakis compounds derived from acetone solvent had the largest emission, while the smallest emission with the shortest decay time was obtained for the product from chloroform solvent. Photoluminescent emission spectra for the compounds from different solvents show the 5D0 → 7F1, 5D0 → 7F2 and 5D0 → 7F3 peaks which are consistent with previously reported results for EuD4TEA. However the intensity of the 5D0 → 7F2 transition shows the 613.5 nm is larger than the 611.7 nm for the products from 1-butanol and methylene chloride. Eu compound from 1-butanol shows a more intense 616.5 nm and 624.2 nm peaks, of which the later peak is almost merged into the background for Eu compounds obtained from the other solvents.

Luminescent properties of lanthanide dibenzoylmethide triethylammonium compounds

Triboluminescence (TL) is defined as the emission of cold light based on mechanical action. In 1999, Sage and Geddes used this property to design a sensor capable of discerning the location of impacts. By coating a structure with various triboluminescent materials, impacts to structures could be monitored with simple light detectors. However, the intensity of most materials is very low. Of the thousands of known triboluminescent materials, only a few can emit enough light to be seen in daylight. One of these materials is europium dibenzoylmethide triethylammonium (EuD4TEA). This material shows 206% of the TL yield compared to the more commonly known manganese-doped zinc sulfide. Due to the high TL yield of EuD4TEA, exploration of the lanthanide series compounds was attempted for different emission wavelengths. This will help to monitor the locations of impacts on structures. This paper will investigate the TL yields, TL decay times, and the spectra of various lanthanide dibenzoylmethide triethylammonium compounds.PACS78.60.Mq, 78.55.Bq, 71.20.Eh

Characterization of Candidate Solar Sail Material Exposed to Space Environmental Effects

Solar sailing is a unique form of propulsion where a spacecraft gains momentum from incident photons. Solar sails are not limited by reaction mass and provide continual acceleration, reduced only by the lifetime of the lightweight film in the space environment and the distance to the Sun. Once thought to be difficult or impossible, solar sailing has come out of science fiction and into the realm of possibility. Any spacecraft using this method would need to deploy a thin sail that could be as large as many kilometers in extent. The availability of strong, ultra lightweight, and radiation resistant materials will determine the future of solar sailing. The National Aeronautics and Space Administrations Marshall Space Flight Center (MSFC) is concentrating research into the utilization of ultra lightweight materials for spacecraft propulsion. The Space Environmental Effects Team at MSFC is actively characterizing candidate solar sail material to evaluate the thermo-optical and mechanical properties after exposure to space environmental effects. This paper will describe the exposure of candidate solar sail materials to emulated space environmental effects including energetic electrons, combined electrons and Ultraviolet radiation, and hypervelocity impact of irradiated solar sail material. This paper will describe the testing procedure and the material characterization results of this investigation.

Changes in half brightness dose due to preparation pressure for YAG:Ce

Previous research shows that certain properties, such as half brightness dose (N/sub 1/2/) and fluorescence intensity, depend on preparation pressure. Phosphor tablets composed of 50% cellulose and 50% yttrium aluminum garnet doped with cerium (YAG:Ce) powders, were created using a Carver press with an applied force of 78 kN. The average 3 MeV proton N/sub 1/2/ for the tablet samples was 11.6 and 36.6 times smaller than equivalent values for the paint and crystal forms of YAG:Ce respectively. It is quite apparent that the application of a large preparation force damages some of the YAG:Ce grains which reduces the N/sub 1/2/. The fluorescence efficiency of the tablets was also less than that measured for the other forms of YAG:Ce.

Emission spectra from ZnS:Mn due to low velocity impacts

Triboluminescence (TL) is the emission of light due to crystal fracture and has been known for centuries. One of the most common examples of TL is the flash created from chewing wintergreen Lifesavers. Since 2003, the authors have been measuring triboluminescent properties of phosphors, of which zinc sulfide doped with manganese (ZnS:Mn) is an example. Preliminary results indicate that impact velocities greater than 0.5 m/s produce measurable TL from ZnS:Mn. To extend this research, the investigation of the emission spectrum was chosen. This differs from using filtered photodetectors in that the spectral composition of fluorescence can be ascertained. Previous research has utilized a variety of schemes that include scratching, crushing, and grinding to generate TL. In our case, the material is activated by a short duration interaction of a dropped mass and a small number of luminescence centers. This research provides a basis for the characterization and selection of materials for future spacecraft impact detection schemes.

Electron Radiation Effects on Candidate Solar Sail Material

Solar sailing is a unique form of propulsion in which a spacecraft gains momentum from incident photons. Solar sails are not limited by reaction mass and provide continual acceleration, reduced only by the lifetime of the lightweight film in the space environment and the distance to the Sun. Once thought to be difficult or impossible, solar sailing has come out of science fiction and into the realm of possibility. Any spacecraft using this propulsion method would need to deploy a thin sail that could be as large as many kilometres in extent. The availability of strong, ultra lightweight, and radiation-resistant materials will determine the future of solar sailing. The National Aeronautics and Space Administrations (NASA) Marshall Space Flight Center (MSFC) is concentrating research into the utilization of ultra lightweight materials for spacecraft propulsion. The Space Environmental Effects Team at MSFC is actively characterizing candidate solar sail material to evaluate the thermo-optical and mechanical properties after exposure to space environmental effects. This paper will describe the irradiation of candidate solar sail materials to energetic electrons, in vacuum, in an effort to determine the in-space operational survivability of several candidate sail materials. Results from this research indicate that the candidate sail materials can survive significant doses of electron radiation while under high uniaxial stress.

Report on the Acadiana Research Laboratory nuclear microprobe system

The Acadiana Research Laboratory of the University of Louisiana at Lafayette provides high energy ion beams for materials research. Major components of the ion beam systems include a National Electrostatics Corporation (NEC) 1.7 MV tandem Pelletron accelerator system with both SNICS and RF ion sources and a Varian CF-4 200 kV implanter. The NEC Pelletron has three operational beamlines that provide a wide range of capabilities for materials modification and analysis, including such techniques as PIXE, PIGE, RBS, RFS, TOF-ERDA and ion implantation. An Oxford Microbeams Ltd. microprobe system was recently declared operational with the attainment of a 1.5 μm×2.0 μm beam spot size. Microprobe techniques presently available include μPIXE, μRBS and scanning transmission ion microscopy (STIM).

Measurement of the triboluminescent properties for europium and samarium tetrakis dibenzoylmethide triethylammonium

AbstractTriboluminescence (TL) is the emission of cold light that is created when materials are fractured. Europium tetrakis dibenzoylmethide triethylammonium (EuD4TEA) is one of the brightest triboluminescent materials that exist. In 2010, efforts began to introduce additives to the synthesis to increase the triboluminescent yield of EuD4TEA. To date, this research has increased the overall emission yield of EuD4TEA by nearly two fold. This paper explores the effects of adding samarium to EuD4TEA. The effects of this additive on the decay time and photoluminescent emission spectra are reported. In addition, the effects of europium on samarium tetrakis dibenzoylmethide triethylammonium are also determined. The effects of europium on the decay time and photoluminescent emission spectra are also reported. Results will show that both additives have an adverse effect on the triboluminescent emission yield.