Development of thin films of thermographic phosphors for spatial resolved temperature measurements using sputtering techniques

Abstract: Two thermographic phosphors materials for surface temperature measurements, praseodymium-doped calcium titanate, CaTiO3:Pr3+, and chromium-doped gadolinium gallium oxide, Gd3Ga5O12:Cr3+, have been successfully deposited on stainless steel substrates by radio frequency magnetron sputtering. For the sputtering process, phosphor targets were prepared using sol-gel combustion (for CaTiO3:Pr3+) and solid-state reactions (for Gd3Ga5O12:Cr3), combined with high temperature sintering. The physical, chemical and luminescence properties of the phosphor films have been evaluated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and laser diagnostics. The results showed that the luminescence features of the thin films were restored by heat treatment after the sputtering deposition. The CaTiO3:Pr3+ film showed low temperature sensitivity of its luminescence lifetime and poor precision of the temperature determination, which could limit its thermographic functionality. Contrary, the Gd3Ga5O12:Cr3+ film exhibited appropriate temperature sensitivity with adequate precision of the temperature determination, proving to be suitable for thermographic applications. An evaluation of the two-dimensional luminescence characteristics of the Gd3Ga5O12:Cr3+ thin film revealed spatial inhomogeneities in the luminescence lifetime of the film. A study on Gd3Ga5O12:Cr3+ powders samples, varying the doping concentration and co-doping with cerium, was included with the aim of increasing the understanding about the luminescence characteristics of this phosphor. These results showed that increasing the Cr doping concentration only changes significantly the luminescence lifetime for concentrations above 1 mol%, while temperature sensitivity and precision of the temperature determination are maintained. Co-doping with small amounts of cerium reduces the afterglow of the Gd3Ga5O12:Cr3+ phosphor. However, an excess of cerium could significantly affect the luminescence properties, resulting in poor precision of the temperature determinationResumen: Se evaluó el desempeño de la pulverización catódica (sputtering) para producir recubrimientos de materiales fosforescentes para la medición de temperaturas superficiales. Se depositaron exitosamente películas delgadas de titanato de calcio dopado con praseodímio, CaTiO3:Pr3+, y granate de gadolinio y galio dopado con cromo, Gd3Ga5O12:Cr3+, en sustratos de acero inoxidable, utilizando sputtering por radiofrecuencia combinada con campo magnético. Los objetivos para el proceso de sputtering se prepararon mediante las técnicas sol-gel con combustión (para el CaTiO3:Pr3+) y reacciones de estado sólido (para el Gd3Ga5O12:Cr3) combinadas con sinterización a alta temperatura. Se evaluaron las propiedades físicas, químicas y de luminiscencia de las películas delgadas, mediante difracción de rayos X (DRX), espectroscopia de fotoelectrones emitidos por rayos X (XPS) y diagnóstico láser. Los resultados mostraron que las propiedades de luminiscencia de las películas fueron restablecidas con tratamiento térmico después de la deposición por sputtering. La película de CaTiO3:Pr3+ mostró una baja sensibilidad de la duración de la luminiscencia con el cambio de temperatura y una baja precisión en la determinación de la temperatura, lo cual podría limitar su funcionalidad para fines de termometría. Por el contrario, la película de Gd3Ga5O12:Cr3+ mostró una sensibilidad apropiada de la duración de la luminiscencia con el cambio de temperatura con una alta precisión en la determinación de la temperatura, probando que esta película delgada es adecuada para aplicaciones de termometría de superficies. Una evaluación de las características de luminiscencia en dos dimensiones de la película de Gd3Ga5O12:Cr3+ reveló una homogeneidad relativamente baja en la duración de la luminiscencia de la película. Se estudió para muestras en polvo de Gd3Ga5O12:Cr3+, el efecto de la concentración del cromo y el codopado con cerio, con el fin de incrementar el entendimiento de las propiedades de luminiscencia de este material fosforescenteMaestrí

Development of the gas phase laser induced phosphorscence technique and soot measurements in flame using laser induced incandescence

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University LondonThermometry measurements were carried out using planar laser induced phosphorescence in conjunction with thermographic phosphors in heated turbulent jets and laminar flames in order to further develop the technique for usage in flames. Two dimensional thermometry measurements are essential to improve the understanding of combustion processes, as temperature governs soot pyrolysis, leading to soot formation. Two particular thermographic phosphors, BAM and YAG:Dy were tested and compared and it was found that they were unsuitable for gas phase flame thermometry measurements. Soot volume fraction measurements were carried out using planar two colour laser induced incandescence in gaseous and liquid fuel flames. The gas fuel flames were diluted with nitrogen, carbon dioxide and hydrogen individually and then with nitrogen and hydrogen together, as well as carbon dioxide and hydrogen together, separately. Results revealed the dilution effects of the gases on the soot formation process, where increasing nitrogen percentage in the flow decreased SVF, carbon dioxide reduced it further and hydrogen showed no marked difference. Biodiesels were compared with each other and with diesel in a wick burner in order to analyse their compositional effects on soot. Biodiesel composition was measured using gas chromatography. The sooting tendencies of the biodiesels were as expected, fuels with a longer average carbon chain length and a higher degree of unsaturation were found to produce more soot than shorter, more saturated fuels. Diesel was sootier than all of the biofuels tested, due to containing aromatics and a lower oxygen content. A pilot study was also done, where the performance and emissions of biofuels and biofuel-diesel blends were tested in a gas turbine engine, in order to relate the investigation to real world situations.Thomas Gerald Gray Charitable Trust,Phosphor Technology Lt

Phosphor Thermometry on Surfaces - A Study of its Methodology and its Practical Applications

Phosphor Thermometry is a term describing an optical measurement technique for remote temperature sensing. Its working principle is based on the temperature-sensitive emission characteristics of certain ceramic substances termed thermographic phosphors. These inorganic materials can either be coated on objects for surface thermometry or be seeded into the gas phase or into liquid flows as solid particles. After optical excitation, often achieved using pulsed laser systems, the phosphor emits an extended and typically red-shifted afterglow referred to as phosphorescence. As the temperature changes, either the temporal or the spectral composition of the phosphorescence emission can be used to determine temperatures through comparison with the results of temperature calibration, carried out earlier. In many applications, temperatures both at various points and in two-dimensional fields have been characterised with a high degree of temporal and spatial resolution by use of thermographic phosphors. The combined sensitivities of different phosphors span a temperature range extending from cryogenic temperatures up to approximately 2000 K. In the present study, the reader is introduced to the physical basis of phosphor luminescence and to utilization of the optical properties involved for temperature measurement. The thesis also examines various means of reducing measurement uncertainty in surface phosphor thermometry. This is done in a series of experimental studies concerned with the characterization and treatment of various error sources during temperature calibration, signal detection and data evaluation. A major factor considered here is that of the coating thickness. It appears to have an intrusive effect on surface temperatures in applications involving both high local and temporal thermal gradients. The effects of instrumentation on signal detection are also investigated. The measurement accuracy was found to depend very much upon the consistency, achieved in the reproduction of the operating conditions from the temperature calibrations carried out to the experiments. This can be attributed to non-linear signal transformations that occur during detection. Even two detectors nominally identical were shown to exhibit large differences in the linearity of the signal response. Unfortunately, the linear workspace of many detectors is confined to very low signal values, the measurement precision being comparably poor due to the low signal-to-noise ratios involved. In order to improve the measurement precision without reducing the accuracy of the results, higher signal levels could be accessed through measures to compensate for detector-specific non-linearities. The signal responses to variations in operating conditions of several different point detectors and imaging devices were characterized, providing a basis for effective means of signal correction. Interest in uncertainty reduction here also led to the investigation of means of signal processing enhancement. Temperature sensitivity was found to be a quantity which is not determined exclusively by the phosphor itself, it is also depending on the operator's choice of conditions for detection and evaluation. For evaluation schemes based on temporal decay transients, the proper choice of a time window for evaluation was found to play an important role. Finally, the versatility of phosphor thermometry as applied to surfaces was demonstrated in several industry-relevant applications, including a car engine, an aircraft turbine and a large-bore two-stroke diesel engine for marine vessels

Remote measurement of temperature using laser-induced luminescence

A technique is required to measure the temperature of rotating compressor wheels at speeds of up to 80000 rpm and within the range 100°C to 250°C. Present available methods such as emissivity cannot be used due to the substantial interference from surrounding objects, nor can thermocouples due to their effect on the airflow within the compressor. Laser induced fluorescence (LIF) has been used successfully on rotating objects, but at speeds much less than the speeds which are required for implementation on a running compressor. Previous work with LIF has related the decay time of the fluorescence with temperature, this cannot be accurately implemented at high speeds due to the short amount of time that fluorescence is available to the detector, and as such as short amount of the decay curve is collected. The fluorescent peak positions and intensities are to be used for temperature measurement in this project. [Continues.

Feasibility of luminescent multilayer sol-gel thermal barrier coating manufacturing for future applications in through-thickness temperature gradient sensing

This paper investigates the feasibility of manufacturing sol-gel multilayer thermal barrier coatings (TBC) functionalized with different lanthanide ions Ln3 + having distinct photo-luminescence emission wavelengths (Ln = Sm, Eu, Dy, Er, Tm) for future applications in temperature gradient sensing. Ln3 + doped 9.75 mol% yttria stabilized zirconia (YSZ) powders were produced to study the effect of activator concentration on luminescence intensity and host matrix crystal structure. Self-quenching was found to limit the maximum signal-to-noise ratio achievable with Sm3 +, Dy3 +, Er3 + and Tm3 + activators, which was not the case for Eu3 + in the 1–10 mol% range. The increase in activator was found to affect the crystal structure of YSZ. A solution was proposed that suppressed this effect while significantly increasing the luminescence intensity of all activators. Finally a TBC sensor prototype integrating Eu3 +, Er3 + and Dy3 + doped layers distributed throughout the thickness was successfully deposited by a dip-coating sol-gel process and showed promising through-thickness luminescence sensing capabilities

Temperature dependence of luminescence inorganic phosphors doped with rare earth ions

Fosfori na bazi retkih zemalja predstavljaju važnu grupu materijala koja nalazi primenu u medicinskoj tomografiji, fizici visoke energije, proizvodnji scintilatora, lampi i displeja [1] . Upotreba ovih materijala kao temperaturskih senzora u poslednje vreme postala je veoma interesantna [2] [3]. Predmet istraživanja ovog rada bio je temperatursko gašenje luminescencije fosfora na bazi retkih zemalja. Analizirane su matrice ortovanadata i seskvioksida dopirane jonima europijuma (Eu3+), disprozijuma (Dy3+) i samarijuma (Sm3+). Pokazana je temperaturska zavisnost luminescentnih emisionih spektara ovih materijala, koja nalazi praktičnu primenu u merenju temperature. Kako rezultati dobijeni merenjem emisionih spektara u funkciji temperature nisu pogodni za opisivanje fenomena temperaturskog gašenja luminescencije, izvršena su merenja vremena života pobuđenog stanja dopantnih jona. Pokazano je da postojeći modeli, model multifononske relaksacije i model neradijativnog pražnjenja preko CT nivoa (nivoi sa prenosom naelektrisanja, engl. Charge transfer states) ne daju zadovoljavajuće rezultate. Analizom ekscitacionih spektara pokazano je da CT nivo nema fiksnu vrednost već da se njegova energija menja sa promenom temperature. Na osnovu datih merenih rezultata izvršeno je unapređenje postojećeg modela neradijativnog pražnjenja preko CT nivoa koji uključuje temperatursku zavisnost energije CT stanja. Poređenje postojećih modela i modela temperaturski zavisnog CT stanja pokazano je bolje slaganje ovog modela sa eksperimentalnim rezultatima.The rare earth based inorganic phosphors are a significant group of materials which are commonly used in medical tomography, high energy physics, the production of scintillators, lamps and displays. [1] Using these materials as temperature sensors has lately become a very interesting topic. [2] [3] The topic of this research is temperature quenching of luminescence of rare earth doped phosphors. The matrix of orthovanadates and sesquioxides doped with Europium (Eu3+), Dysprosium (Dy3+) i Samarium (Sm3+) ions has been analyzed. We have shown the temperature dependence of luminescent emission spectra of these materials and their practical use in the temperature measurement. Lifetime measurements are performed for the excited states of the rare earth ions due to the fact that the results obtained from testing the emission spectra as a function of temperature were not suitable to describe the temperature quenching of luminescence. This thesis showed that the existing models, multiphonon relaxation and temperature quenching through CT (charge transfer) state, do not provide the satisfactory results. By analyzing the excitation spectra we have shown that the CT level does not have a fixed value but its energy changes with the temperature change. Based on the experimental results, an improvement of the existing model (temperature quenching through the CT state) has been given, taking into account the temperature dependence of the CT state. The comparison of the temperature dependent CT state model to the existing models has shown its better correspondence to the obtained results

NASA Tech Briefs, December 1988

This month's technical section includes forecasts for 1989 and beyond by NASA experts in the following fields: Integrated Circuits; Communications; Computational Fluid Dynamics; Ceramics; Image Processing; Sensors; Dynamic Power; Superconductivity; Artificial Intelligence; and Flow Cytometry. The quotes provide a brief overview of emerging trends, and describe inventions and innovations being developed by NASA, other government agencies, and private industry that could make a significant impact in coming years. A second bonus feature in this month's issue is the expanded subject index that begins on page 98. The index contains cross-referenced listings for all technical briefs appearing in NASA Tech Briefs during 1988

Aeronautical engineering: A continuing bibliography with indexes (supplement 259)

This bibliography lists 774 reports, articles, and other documents introduced into the NASA scientific and technical information system in November, 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Thermographic particle image velocimetry: from phosphorescence to incandescence

Thermographic PIV is a promising technique that enables simultaneous temperature and velocity imaging in flows with intentional seeded phosphor particles. This is highly attractive to researchers in fluid mechanics and combustion, as it directly visualizes the heat and mass transfer process in turbulent flows/flames. However, three problems for this technique are: (a) it requires two lasers and three cameras running simultaneously, making it a high-cost technique; (b) several recent studies reported the multiple scattering effects for gas-phase phosphor thermometry, which may severely bias the temperature measurement for certain flow configurations; and (c) the phosphorescent emission disappears at high temperature due to thermal quenching, which limits the temperature measurements to mostly non-reacting cases below 1100 K. This dissertation is aimed at providing solutions to the issues described above. To reduce the cost of the current thermographic PIV setup, a simplified version is proposed which uses a double-pulsed laser with UV capacity and two CCD cameras operating in the double-frame mode. This experiment proves that, apart from Mie scattering, phosphorescence image pairs can also be used to perform cross-correlation and calculate the vector field. Therefore both velocity and temperature field can be extracted from phosphorescence emissions excited by a single laser (UV-PIV). Thermographic PIV with this simplified setup is demonstrated on an electrically heated air jet, and 3 K accuracy is achieved in the core region of the jet, by comparing with a thermocouple scan. A novel calibration process is also proposed to eliminate the influence of non-uniform laser profile on the temperature measurements. The same technique is also applied to visualize heat transfer in an impinging jet. By correlating the instantaneous gaseous temperature fields with the averaged \textit{Nu} profiles derived from the wall temperature, the role of vortical structures in heat transfer is investigated and discussed. During the application of thermographic PIV, the problem of multiple scattering emerged and has been reported by several studies, especially for cases where an excessive seeding is used. Multiple scattering was found to reduce the spatial resolution and bias the temperature measurements. A recent study demonstrated that the Structured Laser Illumination Planar Imaging (SLIPI) technique could effectively remove multiple scattering and near-wall effects from the LIP image. However, it is well known that the emission spectrum of some most commonly used thermographic phosphors is sensitive to the changes in laser fluence, whilst SLIPI intentionally modulates the laser profiles and thus may bring in uncertainty into the temperature retrieval. This has yet not been discussed in the literature. In this dissertation, a numerical analysis is conducted, by generating artificial laser induced phosphorescence images, to investigate the effects that SLIPI may have on the temperature measurements. To implement simultaneous temperature and velocity measurements in flames, an entirely new approach of thermographic PIV is proposed in this dissertation. This new version is based on laser-induced incandescence (LII), rather than phosphorescence. Submicron black particles are seeded into a flame, and further heated by a high-energy top-hat laser sheet to several thousands kelvin. The particle temperature $T_\mathrm{p}$ can be measured by two-color pyrometry, where the temperature increase $\Delta T$ due to laser absorption can be determined by conducting an {\em in-situ} calibration. Thus the local temperature $T_0$ can be indirectly determined by subtracting $\Delta T$ from $T_\mathrm{p}$. The same particle can also be used as PIV tracers. The concept and fundamentals of this new thermographic PIV approach are described in this thesis. The combination of LII and PIV is also applied as a tool to measure the gas-phase velocity in a two-phase flow, which is a canonical problem for multiphase flow studies.Part of the research presented in this thesis was funded by University Technology Malaysia (UTM) under grant number RG8426