Surface Thermometry Using Laser Induced Phosphorescence Applied in the Afterburner of an Aircraft Turbofan Engine

Laser-induced phosphorescence (LIP) is a relatively recent and versatile development for studying flow dynamics. This work investigates certain lanthanide-based molecular complexes for their use in LIP for high-speed sprays. Lanthanide complexes in solutions have been shown to possess long phosphorescence lifetimes (∼1-2 ms) and to emit light in the visible wavelength range. In particular, europium and terbium complexes are investigated using fluorescence/phosphorescence spectrometry, showing that europium-thenoyltrifluoracetone-trioctylphosphineoxide (Eu-TTA-TOPO) can be easily and efficiently excited using a standard frequency-tripled Nd:YAG laser. The emitted spectrum, with maximum intensity at a wavelength of 614 nm, is shown not to vary strongly with temperature (293-383 K). The decay constant of the phosphorescence, while independent of ambient pressure, decreases by approximately 12 μs/K between 323 and 373 K, with the base level of the decay constant dependent on the used solvent. The complex does not luminesce in the gas or solid state, meaning only the liquid phase is visualized, even in an evaporating spray. By using an internally excited spray containing the phosphorescent complex, the effect of vaporization is shown through the decrease in measured intensity over the length of the spray, together with droplet size measurements using interferometric particle imaging. This study shows that LIP, using the Eu-TTA-TOPO complex, can be used with different solvents, including diesel surrogates. Furthermore, it can be easily handled and used in sprays to investigate spray breakup and evaporation.

The solid luminescent materials that convert energy into electromagnetic radiation, usually in the visible region, are termed as phosphor materials. The emission of electromagnetic radiation or light is called luminescence, which is the basic mechanism behind phosphors or luminescent materials. Based on various excitation sources, the luminescence has many classifications like photoluminescence, chemiluminescence, bioluminescence, radioluminescence, and electroluminescence. Phosphors are generally made from host lattices, in which a small amount of impurities or dopants or activators are added intentionally. These impurities can be transition metal ions, rare earth (RE) ions, or complex ions. Also, there is a vast area of host materials are available as silicates, oxides, titanates, molybdates, tungstates, and others. An efficient phosphor material for luminescence applications, we should choose suitable host material and activator ion. For this, there are a number of phosphor synthesis methods available, which affect the physical 302and luminescence properties of the phosphor material. Also, the phosphor materials find many applications in various fields and some of them include lighting applications, cathode ray tubes, scintillators, display devices, long persistent phosphors, light emitting diodes, organic fluorescent pigments, and others. This is the theme of this chapter. In this chapter, we discuss about the phosphors, various luminescence and their basic mechanisms in Sections 14.1 and 14.2. Sections 14.3, 14.4, and 14.5 briefly introduce the importance and properties of activators (dopants), codopants, and host materials used in the phosphor material, respectively. Various phosphor synthesis methods and their advantages are explained in Section 14.6. Finally, Section 14.7 deals with various applications of phosphor materials and important optical properties of some of RE-doped oxide phosphors are also included.

Phosphor powder and phosphor-binder mixtures are successfully employed for temperature calibration measurements by using laser-induced phosphorescence (LIP) technique with an emphasis on higher precisions and accuracies than other non-intrusive methods. The phosphorescence intensities are used to perform these calibrations in three different strategies. The influence of laser power regular changes on particles heating and the calibration analyses is also carried out. A pulsed laser at 355 nm was used for exciting specimens of the phosphor powder as well as the phosphor-binder mixtures. The laser beam was directed onto the specimens and varied in three laser power levels (LPLs). The samples were kept in an oven with temperatures ranging from room temperature up to 1800 °C. The three strategies which are expressed in terms of non-dimensional intensity versus wavelength (NDI-W), normalised intensity (NI) and intensity ratio (IR) were used for the calibration assessments. A modified IR was compared with two different IRs. A precision of around ± (0.50-1.41)% was attained for different calibration methods. This research confirmed that these calibrations are possible using three different strategies, given high precisions and accuracies. The laser power alternations influenced the NI and do affect neither the NDI-W nor the IR curves. The laser radiation does not play any role for heating the particles of the studied powder.

Nanocrystal rods of Eu3+/Tb3+-co-doped ZrO2 were synthesized using a simple chemical precipitation technique. Both ions were successfully doped into the Zr4+ ion site in a mixed structure containing both monoclinic and tetragonal phases. The Eu3+ or Tb3+ singly doped zirconia produced red and green luminescence which are characteristics of Eu3+ and Tb3+ ions, respectively. The co-doped zirconia samples produced blue emission from defect states transitions in the host ZrO2, red and green luminescence from dopant ions giving cool to warm white light emissions. The phosphors were efficiently excited by ultraviolet and near-ultraviolet/blue radiations giving white and red light, respectively. The decay lifetime was found to increase with increasing donor ion concentration contrary to conventional observations reported by previous researchers. Weak quadrupole–quatdrupole multipolar process was responsible for energy transfer from Tb3+ (donor) ion to Eu3+ ion. No energy back-transfer from Eu3+ to Tb3+ ion was observed from the excitation spectra. Temperature-dependent photoluminescence shows the presence of defects at low temperature, but these defects vanished at room temperature and beyond. The Eu3+/Tb3+-co-doped ZrO2 nanocrystal rod is a potential phosphor for white light application using UV as an excitation source. Thermoluminescence measurements show that the inclusion of Tb3+ ion increases trap depths in the host zirconia.

18 - Thermoluminescent study of borates for dosimetric applications

A novel passive interface circuit with gain for nongenerating (active, i.e., excited/driven) sensors in differential or bridge configuration is presented. The circuit is very simple and consists of only one transformer in the output diagonal of the equivalent bridge configuration comprised of sensor(s), bridge completion impedances, and excitation source. It can be used with resistive, capacitive, inductive, eddy-current, and similar sensors for measurement of temperature, displacement, pressure, torque, etc. The gain achieved depends on the transformer voltage ratio, $n$ . Unlike the usual transformer application for voltage raise (gain) where the gain is proportional to $n$ , in this circuit, the high gain is achieved with $n$ close to 1. This is due to positive feedback introduced into the circuit. Transformers with voltage ratios close to 1 exhibit much less leakage and smaller losses which can degrade the (ideal) gain. With current on-chip transformers or miniature transformers available on the market, the practical gain can reach 20 dB. The circuit can be easily integrated into various MEMS sensors. As the circuit is entirely passive, its application extends far beyond the usual semiconductor temperature limits. Depending on the transformer technology, the circuit can be used in a very cold (e.g., cryogenic) or very hot environment (e.g., steam and gas turbines, jet engines, rockets, down-hole drilling, etc.) or exposed to nuclear radiation.

The introduction of solid catalysts into a traditionally non-catalytic free-radical process such as combustion occurred in recent years under the influence of environmental pressures. The major applications of catalytic combustion are two-fold: at low temperatures to eliminate volatile organic compounds (VOCs) and at high temperatures (>1000°C) to reduce NOx emission from gas turbines, jet motors, etc. It is the high temperature application that is reviewed here. Some recent developments in high-temperature catalytic combustion are trend setters in catalysis and hence of particular interest. For instance, novel materials are being developed for catalytic applications above 1000°C for sustained operation longer than one year. Where material/catalyst developments are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid (catalytic + thermal) reactors.

Apart from the temperature, four parameters were investigated for their impact on the phosphorescence characteristics of Mg4FGeO6:Mn with regards to phosphor thermometry: the dopant concentration, the laser pulse energy, gas compositional and pressure effects as well as irreversible changes due to heat treatments. Five specially produced phosphors with different dopant concentrations as well as commercially available Mg4FGeO6:Mn were investigated in the form of coatings and pure powder. The phosphorescence was excited by the third harmonic of a pulsed Nd:YAG laser (355 nm). The lifetime decay as well as the emission spectra of the subsequently emitted phosphorescence were determined. Generally, the decay time decreased with increasing dopant concentration, with increasing laser pulse energy and for coatings also with increasing maximum temperature and duration of heat treatments, whereas the impact of the laser power was minimized by a modified evaluation routine of the decay time. Gas compositional and pressure effects did not have a significant influence on the decay time of Mg4FGeO6:Mn. Neither the variation of the dopant concentration nor the exposure to heat treatments influenced the shape of the emission spectra in any way.

Pressure is an important physical parameter and hence its monitoring is very important for different industrial and scientific applications. Although commonly used luminescent pressure sensors (ruby-Al2O3:Cr3+ and SrB4O7:Sm2+) allow optical monitoring of pressure in compressed systems (usually in a diamond anvil cell; DAC), their detection resolution is limited by sensitivity, i.e., pressure response in a form of the detected spectral shift. Here we report, a breakthrough in optical pressure sensing by developing an ultra-sensitive NIR pressure sensor (dλ/dP = 1.766 nm GPa-1). This luminescent manometer is based on the optically active YVO4:Yb3+-Er3+ phosphor material which exhibits the largest spectral shift as a function of pressure compared to other luminescent pressure gauges reported elsewhere. In addition, thanks to the locations of excitation and emission in the NIR range, the developed optical manometer allows high-pressure measurements (without spectral overlapping/interferences) of various luminescent organic and inorganic materials, which are typically excited and can emit in the UV-vis spectral ranges.

Phosphor materials have attracted attention for their potential use in technological application such as optical thermometry, a non-contact temperature sensing technique which is based on the temperature-dependent luminescent properties of these materials. In many cases, these attractive properties are due to the incorporation of rare-earth elements into crystalline lattices, although their preparation is often toxic, costly and scarce. Thus, this study reports on the synthesis and characterization of manganese-doped strontium aluminate (SrAl 12 O 19 :Mn 4+ ), a rare-earth free phosphor for optical thermometry applications. As this magnetoplumbite host matrix typically requires high synthesis temperatures (≥ 1300 °C) to stabilize, a soft chemical route based on the polymeric precursor method was implemented to reduce the preparation temperature. Combining annealing under N 2 atmosphere and applying very fast heating rate, crystallization temperature of the pure magnetoplumbite phase was successfully reduced by approximately 300 °C. The single-phase structure stabilizes at 1000 °C, a temperature notably lower than that required by solid-state reactions or conventional sol-gel methods. Structural characterization via X-ray diffraction (XRD) confirmed the formation of the hexagonal phase, whereas photoluminescence spectroscopy revealed the characteristic red emission of Mn 4+ ions attributed to the 2 E → 4 A 2 transition. Thus, Mn 4+ ions effectively substituted Al 3+ sites in the host lattice, resulting in strong red emission centered at 657 nm with high color purity. Temperature-dependent fluorescence measurements were performed and fluorescence intensity ratio (FIR) analysis indicated that the synthesized phosphors exhibit high thermal sensitivity ( S r-max = 4.41%K -1 ), comparable to rare-earth-doped materials and making the SrAl 12 O 19 :Mn 4+ phosphor a promising and cost-effective candidate for non-contact optical thermometry. • SrAl 12 O 19 :Mn phosphors were prepared via polymeric precursor method • Samples were prepared with annealing under N 2 atmosphere and very fast heating rate • Crystallization temperature of the SrAl 12 O 19 phase was reduced by ~ 300 °C • Luminescence thermometry of red emission due to the 2 E → 4 A 2 transition of Mn 4+ • High thermal sensitivity (4.41%K -1 ), comparable to rare-earth-doped materials

Products made by the method of «wet» winding from composite material are widely used in various indus-tries. The quality of future products is largely determined by the tension with which the «wet» tape is placed on the product. Until now, the electric motor of the tensioning device was selected from the condition of providing the specified maximum tension value of the composite tape, without taking into account the specific features of the tensioning device used and the geometry of the wound product. However, when winding a product with a complex geometric shape, dynamic moments occur in the electric drive, which cause additional heating of the engine. The paper analyzes the tensioning devices used for winding. They are grouped into two classes: linear and angular movement of tension rollers. For the considered tensioning devices, analytical expressions are ob-tained that relate the tension during winding with the force that the Executive electric motor must provide in static and dynamic modes. A method for selecting the drive power of tensioning devices is proposed, which takes into account the features of winding composite products made of «wet» composite material. As an exam-ple, the drive of a tensioning device is calculated when winding a pressure cylinder with a diameter of 0.2 m. the Calculations are carried out taking into account the possibility of using a worm self-braking gearbox or a planetary gearbox. Graphs of the dependence of static and dynamic moments on the motor shaft are plotted. It is shown that the use of a worm gearbox requires a more powerful drive, but when using a planetary gearbox, the electric motor must be able to stand under full load. The results obtained in this work can be used in the de-sign of new winding equipment or modernization of existing ones.

We present an experimental apparatus to control and visualize the response of a liquid target to a laser-induced vaporization. We use a millimeter-sized drop as target and present two liquid-dye solutions that allow a variation of the absorption coefficient of the laser light in the drop by seven orders of magnitude. The excitation source is a Q-switched Nd:YAG laser at its frequency-doubled wavelength emitting nanosecond pulses with energy densities above the local vaporization threshold. The absorption of the laser energy leads to a large-scale liquid motion at time scales that are separated by several orders of magnitude, which we spatiotemporally resolve by a combination of ultra-high-speed and stroboscopic high-resolution imaging in two orthogonal views. Surprisingly, the large-scale liquid motion upon laser impact is completely controlled by the spatial energy distribution obtained by a precise beam-shaping technique. The apparatus demonstrates the potential for accurate and quantitative studies of laser-matter interactions.

Carbon-based nanomaterials are promising for a wide range of biomedical applications, i.e. drug delivery, therapy, and imaging including photoacoustic tomography, where they can serve as contrast agents, biocompatibility and biodistribution of which should be assessed before clinical setting. In this paper, localization of carbon flurooxide nanoparticles, carbon nanodots from β-alanine, carbon nanodots from urea and citric acid and glucose-ethylenediamine nanoparticles (NPs) in organs of Wistar rats were studied by photoacoustic measurements after 24 h of their intravenous injection. 16 ns light pulse from a Q-switched Nd:YAG laser with 1064 nm wavelength was used as an excitation source. The laser-induced photoacoustic signals were recorded with a ring piezoelectric detector. Light absorption by carbon NPs resulted in noticeable enhancement of the photoacoustic amplitude in the tissues where the NPs were accumulated. The NPs were preferably accumulated in liver, kidneys and spleen, and to a lesser extent in heart and gastrocnemius muscles. Together with remarkable fluorescent properties of the studied carbon nanomaterials, their photoacoustic responses allow their application for bi-modal fluorescence-photoacoustic bio-imaging.

Previously direct measurements of the self-trapping time of 1 s excitons in KI was reported. In this paper, measurements for RbI are described. Picosecond pulses of the fifth harmonic (212.8 nm) of a Nd 3+ : YAG laser, which can directly generate the 1 s excitons are used as the excitation source. The rise time of the E x luminescence is measured at 4.2 K. From the observed rise time, the self-trapping time is estimated to be 2.0±0.5 ns. The height of the adiabatic potential barrier separating the free and self-trapped exciton states is measured to be 18 and 30 meV for RbI and KI, respectively. The self-trapping time and the barrier height in RbI and KI are compared, and their changes with changing material are discussed on the basis of the theoretical calculation.

In this paper, we present the molecular density distribution measurement in turbulent nitrogen jet (Re ≈ 3×103), using acetone as molecular tracer. The tracer was seeded in the nitrogen jet by purging through the liquid acetone at ambient temperature. Planar laser sheet of 266 nm wavelength from frequency quadrupled, Q-switched, Nd:YAG laser was used as an excitation source. Emitted fluorescence images of jet flow field were recorded on CMOS camera. The dependence of planar laser induced fluorescence (PLIF) intensity on acetone vapor density was used to convert PLIF image of nitrogen jet into the density image on pixel-by-pixel basis. Instantaneous quantitative density image of nitrogen jet, seeded with acetone, was obtained. The arrowhead-shaped coherent turbulent structures were observed in the present work. It was found that coherent structures were non-overlapping with separate boundaries. Breaking of coherent structures into turbulence was clearly observed above four times jet width.