Kamala N. Bhat

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

Photonic crystals: Crystal growth processing and physical properties

Publisher Summary This chapter discusses crystal-growth fundamentals and the dependence of the crystal-growth process on the physical and chemical state of the solid–liquid interface. Convection is a key transport mechanism that affects the shape of the crystal–melt interface, the concentration distribution, and macro–micro defects. However, this chapter focuses on only basic differential equations and the simplest concepts—such as a few important nondimensional numbers (Re, Gr, Pr, Sc, Ra, and Ma). Crystal growth by the Czochralski, modified Bridgman–Stockbarger, top-seeded solution, and low-temperature solution growth methods are summarized and adequate details are given for fabricating the systems designed and used in laboratory for the growth of high-quality crystals. To further assist in designing and fabricating good equipment for growing crystals by melt processes, information on heating methods, temperature control techniques, and the selection of suitable crucible materials is provided.

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.

Theoretical and experimental study of the second-order polarizabilities of Schiff's bases for nonlinear optical applications

Abstract A series of twenty-four Schiffs bases was synthesized and nonresonant static molecular second order polarizabilities (β) of these compounds were theoretically calculated and compared with experimental values. The computational method employed obtained: (a) values of polarization versus static electric fields using a semiempirical Hamiltonian; (b) all tensor elements of β by performing polynomial fits of the former data, within the finite-field approach. The experimental values were obtained using a modified electric field induced second harmonic generation (EFISH) experiment with 1,4-dioxane as the solvent. The measured quantities were the projection of β on μ (the permanent dipole moment), relative to MNA (2-methyl-4-nitroaniline). The correlation between the predicted static molecular quantities and their corresponding experimental values was 0.95 (based on a simple least-squares regression forced through the origin). A factor of 8.7 ± 0.3 was determined to be the adjustment parameter for Schiffs bases to account for the solvent and dispersion effects at the fundamental wavelength of 1064 nm.

Growth and characteristics of organic and semiorganic nonlinear optical crystals

The growth, synthesis and characteristics of a new organic nonlinear optical crystal, a derivative of Schiff base compounds, 4-nitrobenzylidene-4-chloroaniline are reported. Good-quality crystals have been successfully grown using Bridgman-Stockbarger (BS) Technique. The organic crystal, 4-nitrobenzylidene-4-chloroaniline, shows good second harmonic generation of 1.064 micron wavelength. A recent work done on the semiorganic nonlinear crystals are reviewed along with results of growth of a few L-arginine phosphate type crystals is presented.

Solid-State 13C Nuclear Magnetic Resonance Spectroscopic Characterization of Soil Organic Matter Fractions in a Forest Ecosystem Subjected to Prescribed Burning and Thinning

Abstract Forest management practices such as prescribed burning and thinning in forest ecosystems may alter the properties of soil organic matter (SOM). In this study, surface soils from the field plots of Bankhead National Forest, Alabama were used to investigate the possible thinning- and burning-induced SOM transformations. Elemental analysis and solid state cross polarization magic angle spinning nuclear magnetic resonance (CPMAS 13 C NMR) spectroscopy was used to characterize SOM forms in whole soils, humic substances, and density-based fractions. Our data revealed that the changes in SOM fractions due to the repeated burn treatments carried out in this ecosystem were involved mainly with alkyl C, O-alkyl C, and carbohydrate functional groups, implying that most prominent reactions occurred involved dehydrogenation, de-oxygenation, and decarboxylation. In addition, burning and thinning treatments might have also affected the distribution and composition of free and occluded particulate SOM fractions. The limited structural changes in the SOM fractions suggested that low intensity fire treatments applied to this ecosystem will not have severe impacts on creating major structural changes in SOM forms.

Europium Tetrakis Dibenzoylmethide Triethylammonium: Synthesis, Additives, and Applications Review

There are a number of techniques currently being used for damage detection and monitoring of civil, aerospace, and military structures and aircraft. However, the major drawbacks of the current techniques are that they do not provide in situ and distributed sensing. Wiedemann and Schmidt defined triboluminescence (TL) as the emission of light produced by mechanical action. In recent years, triboluminescent materials have been proposed for use as the active element in smart structural sensors. To sense damage, these materials would be embedded into the structure. If damage occurs to this structure, the embedded triboluminescent material would give off visible light. This light could be transferred by lightweight fiber optics or wireless detector to a computer-based detection system to warn occupants in real time that a significant impact event has occurred. In addition, the triboluminescent based sensor could allow for real-time monitoring of both the magnitude and location of damage to the host structure. One of the brightest triboluminescent materials currently known is europium tetrakis dibenzoylmethide triethylammonium (EuD4TEA). This research delved into the feasibility of enhancing the properties of EuD4TEA by (a) modifying the synthesis process and (b) determining the reproducibility of the synthetic procedure by measuring the batch variation error. Further, the study evaluated the possible techniques that can be incorporated in to the synthesis technique to enhance the TL by (a) introducing various inorganic and organic dopants; (b) optimizing dopant concentration; (c) studying solvents effects on TL; and (d) evaluating the effects of ionizing radiation on TL. In addition, the research discusses in depth the experimental development of a simple apparatus for the measurement of TL in the laboratory by using a twofold technique consisting of measuring the triboluminecent intensity and/or spectral characterization. This enabled for the determination of a unique decay time for a particular compound. In addition, impact studies have been conducted to correlate the impact energy (velocity) with triboluminescent emission, thus allowing a system to detect and evaluate the magnitude of the impacts. The spectra of these compounds have been analyzed in detail to investigate the cause of luminescence and designate the transitional energy levels for each of the peaks. Finally in order to study the feasibility for structural and/or sensor application, the effect of introducing EuD4TEA into poly(methyl methacrylate) and its impact on the TL emission spectra are determined.