Phosphor Thermometry Research Articles

Full spectrum fitting method: a new approach for instantaneous phosphor thermometry in harsh environments

Full spectrum fitting method: a new approach for instantaneous phosphor thermometry in harsh environments

Experimental investigation on flow characteristics and unsteady heat transfer of noncircular impinging synthetic jets

This study investigates the flow characteristics and unsteady heat transfer of noncircular synthetic jets impinging on a heated plate. Thermographic phosphor thermometry and time-resolved particle image velocimetry are used to acquire quantitative wall temperature and flow field information, respectively. At a constant orifice-to-wall distance (H/De = 7.5), five orifice configurations (circular, square, elliptic with aspect ratio (AR) of 3, and rectangular with ARs of 3 and 5) are examined at a wall temperature of 80 °C. The orifice configuration has a significant effect on the heat transfer and vortex behavior of the impinging synthetic jets. The square orifice displays better stagnation cooling performance with 42% increase in the maximum stagnation cooling coefficient relative to the circular case due to the larger impinging velocity and deeper penetration into the wall shear layer. Axis-switching of the vortex rings is detected for both the elliptic and rectangular orifices before they impinge onto the wall. The axis-switching enhances the near-wall mixing and turbulent kinetic energy in the elliptic and rectangular orifices, and thus heat transfer compared with the circular case. Additionally, stronger vortices and deeper penetration into the wall shear layer are observed in the major-axis plane than in the minor-axis plane, leading to enhanced heat transfer in the major-axis direction. In particular, the rectangular orifice with an AR of 5 induces strong secondary structures in the trailing jet following the primary vortex ring, and these are responsible for the double-peak distribution of wall temperature in the major-axis direction. This is the first time a double-peak temperature distribution has been reported for noncircular impinging synthetic jets. The rectangular orifice with an AR of 5 also yields a larger cross-stream velocity in the minor-axis direction, indicating a stronger wall jet. Thus, among the cases considered in this study, the rectangular orifice with AR = 5 achieves the optimal cooling performance and the maximum time-averaged cooling area reaches more than 14 times the jet orifice area.

Electromagnetic immune phosphor-tipped fibre-optic thermometers

Calibration traceability can be broken where there are significant, unquantified uncertainties. Thermometry in harsh environments using electrical sensors, such as thermocouples or resistance thermometers, can be unpredictably affected by electro-magnetic sources. For this application, phosphor based temperature sensors with fibre-optic connection have been made following two different approaches—phosphor decay time changes and phosphor emission spectral changes—and tested by bombardment with high energy electrons and by measurements in large magnetic fields. Both sets of tests showed good immunity to exposure, and with magnetic field tests significantly better than a thermocouple. Phosphor thermometry therefore has potential to retain traceability in situations where conventional sensors might fail.

Improving the temperature uncertainty of $$ {\text{Mg}}_{4} {\text{FGeO}}_{6} {\text{:Mn}}^{{4 + }} $$ ratio-based phosphor thermometry by using a multi-objective optimization procedure

Improving the temperature uncertainty of $$ {\text{Mg}}_{4} {\text{FGeO}}_{6} {\text{:Mn}}^{{4 + }} $$ ratio-based phosphor thermometry by using a multi-objective optimization procedure

Electromagnetic immune phosphor-tipped fibre-optic thermometers

Abstract Calibration traceability can be broken where there are significant, unquantified uncertainties. Thermometry in harsh environments using electrical sensors, such as thermocouples or resistance thermometers, can be unpredictably affected by electro-magnetic sources. For this application, phosphor based temperature sensors with fibre-optic connection have been made following two different approaches – phosphor decay time changes and phosphor emission spectral changes – and tested by bombardment with high energy electrons and by measurements in large magnetic fields. Both sets of tests showed good immunity to exposure, and with magnetic field tests significantly better than a thermocouple. Phosphor thermometry therefore has potential to retain traceability in situations where conventional sensors might fail.

Probing the multifunctionality of double layered perovskite NaGdMgTeO6:Eu3+ in ratiometric phosphor thermometry and solid-state lighting

The present work deals with synthesis and optical properties of NaGdMgTeO6: x% Eu3+ (x = 2%, 4%, 6%, 8%, 10%, 12%, and 14%) double layered perovskite phosphors synthesized via conventional solid state ceramic route. X-ray diffraction profile along with Rietveld refinement reveals the single phase nature of the compounds. Further Raman and FTIR spectroscopy were carried out to deduce the structural modifications induced by the substitution of Eu3+ ions at Gd3+ site. A direct bandgap of 3.5 eV suggests that these phosphors can be efficiently excited using ultraviolet radiation. The compound can be efficiently excited by 265 nm and gives red emission at 615 nm corresponding to 5D0- 7F2 electric dipole transition of Eu3+ ions. The optimum doping concentration of Eu3+ is obtained as 8 mol% beyond which concentration quenching occurs. Thermal activation energy of the phosphor is evaluated as 0.2 eV. Thermal stability and other phosphor parameters show its potential application in solid state lighting. The relative temperature sensitivity and absolute sensitivity obtained by measuring fluorescence intensity ratio of 5D0→7F1 to 5D0→7F2 is 0.23%K-1 and 0.0072 K−1 respectively. Judd-Ofelt parameters were evaluated which are in good agreement with the results obtained from PL spectra. Judd-Ofelt theory is further extended to evaluate thermometric parameters by considering the emissions from 5D0 and 5D1 thermally coupled energy levels (TCLs) of Eu3+ ions. A good match is observed between thermometric parameters obtained by conventional method and Judd-Ofelt theoretical model. All the results suggested that NaGdMgTeO6: Eu3+ phosphors have potential applications in solid state lighting and optical thermometry.

Precise surface temperature measurements at kHz-rates using phosphor thermometry to study flame-wall interactions in narrow passages

The thermographic phosphor ScVO4:Bi3+ is used to obtain time-resolved surface temperature measurements with sub- °C precision at 5 kHz. Measurements are used to study transient heat loss and flame-wall interactions (FWI) within a dedicated narrow two-wall passage (crevice) in an optically accessible fixed volume chamber. This passage emulates a crevice relevant in many technical environments, where FWI is less understood due to lack of detailed measurements. Chemiluminescence (CH*) imaging is performed simultaneously with phosphor thermometry to resolve how the flame's spatiotemporal features influence the local surface temperature. ScVO4:Bi3+ is benchmarked against Gd3Ga5O12:Cr,Ce, a common phosphor used at low-kHz rates in FWI environments. ScVO4:Bi3+ is shown to offer higher luminescence signal levels and temperature sensitivity as well as negligible cross dependence on the excitation laser fluence, improving the precision and repeatability of the wall temperature measurement. ScVO4:Bi3+ is further used to resolve transient heat loss for variations in crevice spacing and uniquely capture temperature transients associated with flame dynamics. Taking advantage of these precise surface temperature measurements the wall heat flux is calculated with crevice spacing of 1.2 mm, where flame extinction is prevalent. Wall heat flux and estimated quenching distance are reported for flames that actively burn or extinguish at the measurement location.

Synthesis and optical spectroscopy of Na3Y(VO4)2:Eu3+ phosphors for thermometry and display applications.

A new Na3Y(VO4)2:Eu3+ (NYVO:Eu3+) phosphor was prepared using the sol–gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to evaluate phase purity and particle size, respectively. The optical properties were investigated by UV-visible absorption, PL, and PLE spectroscopies. The absorption measurements show the formation of the vanadate host by the presence of its characteristic band in the visible region related to VO43− groups. The experimental results show that the NYVO:Eu3+ phosphors exhibit high-brightness and thermally stable emission. Under near-ultraviolet (UV) excitation, both the broadband emission from VO43− groups and the sharp peak emissions from Eu3+ ions are observed. The highest luminescence intensity was achieved for an optimal europium concentration of 15 mol%. The study of the chromaticity parameters of these compounds gives a thermally stable hot emission in the red domain, with a color purity of about 85%, which qualifies the NYVO:Eu3+ compound as a potential phosphor for light-emitting diode (LED) applications. Thermal sensing using NYVO:Eu3+ phosphors are based on monitoring the luminescence intensity ratio between the NYVO host emission and Eu3+ luminescence lines. Notably, the optical thermometry of NYVO:Eu3+ was characterized based on the fluorescence intensity ratio of VO43− and Eu3+ emissions in the 298–440 K range, with maximum absolute and relative sensitivities of 3.4% K−1 and 0.0032 K−1 respectively and a temperature uncertainty of 0.01. NYVO:Eu3+ can then be considered as a potential red phosphor for application in ultraviolet-pumped white light-emitting diodes and as a potential optical thermometer. It provides new possibilities for the design of multifunctional materials for red light-emitting diodes and for non-contact thermometry.

Two-dimensional lifetime-based kHz surface temperature measurement technique using phosphor thermometry

A kHz phosphor thermometry technique was developed for contactless two-dimensional measurements with Mg4FGeO6: Mn4+ utilizing its rise and decay of the phosphorescence. Different from the traditional method that phosphorescence rises when the decay is complete, high-frequency excitation light was applied in this study, which causes a rise of phosphorescence with an incomplete decay of phosphorescence. This eventually causes the phosphor to emit a waveform signal. Experimental results show that this phosphorescence waveform signal is stable and only affected by temperature when the excitation conditions are fixed. A calibration curve can then be obtained by calculating the ratio of the crests and troughs of the phosphorescence signal. This study shows that the developed method has high precision and is easy to operate for two-dimensional high-frequency temperature measurement.

Investigating photomultiplier tube nonlinearities in high-speed phosphor thermometry using light emitting diode simulated decay curves.

Photomultiplier tube (PMT) nonlinearities relevant for single shot high-speed lifetime phosphor thermometry were investigated by simulating decay curves with a light emitting diode (LED) at repetition rates between 1Hz and 10kHz. The PMT gain, LED decay time, and background radiant flux were also varied to investigate their impact on the measured decay time error. Errors in the measured decay time due to nonlinear PMT performance lead to temperature measurement errors; therefore, having the measured decay time sensitive to only phosphor temperature is highly valuable for more reliable temperature measurements. Photocathode bleaching had a significant impact on the signal level linearity for PMTs with excitation frequency in the kHz regime but had a smaller impact on the decay time error. Space charge effects were most noticeable at high radiant flux levels and high repetition rates. Strong background radiant flux may lead to decay time errors, and a gateable photocathode could be an effective method to reduce decay time errors. The best decay time measurement configuration to maximize precision without sacrificing accuracy is to use PMT gain in the recommended range and the highest radiant flux where the PMT response is still linear. The degree of nonlinearity in the PMT response is partly detector dependent; therefore, the results in this work may differ among detectors; however, the analysis presented in this work provides guidelines for improving the temperature accuracy of kHz lifetime phosphor thermometry measurements.

In-cylinder thermographic PIV combined with phosphor thermometry using ZnO:Zn

Two-dimensional thermographic particle image velocimetry (T-PIV) is presented for the in situ measurement in optically accessible internal combustion (IC) engines. Temperature and velocity measurements are combined using thermographic phosphor particles as tracers for PIV. For three commercially available phosphors (BAM:Eu2+, ZnO, and ZnO:Zn), temperature sensitivity, luminescence intensity at high temperatures and laser-fluence dependence were evaluated for phosphor-coated surfaces in a high-temperature cell. ZnO:Zn was identified as the best-suited candidate for engine in-cylinder measurements and further analyzed in the aerosolized state at temperatures up to 775 K to generate calibration data required for signal quantification in engine experiments. T-PIV was successfully applied in the IC engine to simultaneously obtain instantaneous two-dimensional velocity and temperature fields using the intensity-ratio method. Despite a measurement uncertainty (±1σ basis) of only 3.7 K at 317 K (1.2%) to 24.4 K (4.2%) at 575 K, this technique suffers from low signal intensities due to thermal quenching at increasing temperatures, which leads to reduced accuracy as the piston approaches top dead center. Thermographic measurements were successful to visualize local temperature changes due to evaporative cooling after fuel injection. The measured mean gas temperatures agreed well with zero-dimensional simulations that use additional wall-temperature measurements from thermographic phosphor measurements based on the lifetime method as input for heat transfer calculations.

Detailed assessment of the thermochemistry in a side-wall quenching burner by simultaneous quantitative measurement of CO[formula omitted], CO and temperature using laser diagnostics

This study focuses on exploring the thermochemistry in flame-wall interaction (FWI) for fully premixed side-wall quenching of a laminar, atmospheric-pressure dimethyl ether flame at equivalence ratio Φ=0.83 by simultaneous measurement of CO2 and CO mole fractions and gas phase temperature T. The applied laser diagnostics are dual-pump coherent anti-Stokes Raman spectroscopy (DP-CARS) targeting N2 and CO2, laser-induced fluorescence of CO and OH, as well as thermographic phosphor thermometry. The extension to DP-CARS to study FWI processes is the first of its kind, previous studies only provided (CO,T) measurements. The laser diagnostics are benchmarked and calibrated to an adiabatic test case and assessed in accuracy and precision. Subsequently, the approach is used to measure the thermochemistry close to a quenching wall. The nominal flame-to-wall distances from the experiment well match the numerical simulation data with a marginal offset of 20 µm. Conditioning the thermochemical data with respect to the instantaneous quenching point, named quenching-point conditioning, enables a novel tracing of the wall-parallel chemistry evolution across the quenching location. The study provides the first comparison of experimental three-scalar measurements (CO2,CO,T) with two-dimensional (2D) fully-resolved chemistry and transport (FCT) simulations. The validation of numerical simulations can now rely on the three scalars (CO2,CO,T) instead of the two scalars (CO,T) in past studies. The evaluation reveals that this novel three-scalar measurement allows highly sensitive probing of the thermochemical states and is clearly superior to the previously applied two-scalar approach. CO2 is less affected by the quenching wall compared to CO. Differential diffusion effects are experimentally confirmed by comparison to 2D-FCT, with the (CO2,T) state space being more sensitive than (CO,T). As the experimental methodology proved feasible for laminar operation, a transfer to turbulent cases, where the numerical analysis using direct numerical simulations (DNS) including FCT is limited, appears promising.

Remote optical detection of geometrical defects in aerogels and elastomers using phosphor thermometry

Detecting structural damage in the form of geometrical defects in materials that operate under extreme conditions or serve as critical structural components is essential. In this work, the feasibility of using thermographic phosphors as a non-destructive, remote, instantaneous, and customizable sensing mechanism for detection of structural damage was investigated. The two materials studied were (1) Sylgard 184 elastomer and (2) silica aerogels. Two different types of structural damage were investigated in samples of increasing thickness, up to a maximum of 18 mm. To accurately interpret the results, heat flux measurements were also collected from both material types. The changes in the thermal profile of the material as a result of material defects were used to infer information about the structural health of the material. La2O2S:Eu and Mg3F2GeO4:Mn were chosen for the study since their temperature sensitivity range complemented one another and allowed for measurements from cryogenic to 200 °C. It was determined that fracture and failure in both aerogels and Sylgard 184 could be detected by phosphor thermometry and the limit of its resolution was ultimately determined by the thermal properties of the material, the choice of phosphor, and ambient temperature.

Temperature-dependent x-ray fluorescent response from thermographic phosphors under x-ray excitation

Phosphor thermometry has been successfully applied within several challenging environments. Typically, the thermographic phosphors are excited by an ultraviolet light source, and the temperature-dependent spectral or temporal response is measured. However, this is challenging or impossible in optically thick environments. In addition, emission from other sources (e.g., a flame) may interfere with the optical phosphor emission. A temperature dependent x-ray excitation/emission could alleviate these issues as x-rays could penetrate obscurants with no interference from flame luminosity. In addition, x-ray emission could allow for thermometry within solids while simultaneously x-ray imaging the structural evolution. In this study, select thermographic phosphors were excited via x-ray radiation, and their x-ray emission characteristics were measured at various temperatures. Several of the phosphors showed varying levels of temperature dependence with the strongest sensitivity occurring for YAG:Dy and ZnGa2O4:Mn. This approach opens a path for less intrusive temperature measurements, particularly in optically opaque multiphase and solid phase combustion environments.

Experimental investigation of thermal boundary layers and associated heat loss for transient engine-relevant processes using HRCARS and phosphor thermometry

Design of efficient, downsized piston engines requires a thorough understanding of transient near-wall heat losses. Measurements of the spatially and temporally evolving thermal boundary layer are required to facilitate this knowledge. This work takes advantage of hybrid fs/ps rotational coherent anti-Stokes Raman spectroscopy (HRCARS) to measure single-shot, wall-normal gas temperatures, which provide exclusive access to the thermal boundary layer. Phosphor thermometry is used to measure wall temperature. Measurements are performed in a fixed-volume chamber that operates with a transient pressure rise/decay to simulate engine-relevant compression/expansion events. This simplified environment is conducive for fundamental boundary layer and heat transfer studies associated with engine-relevant processes. The thermal boundary layer development and corresponding heat losses are evaluated within two engine-relevant regimes: (1) an unburned-gas regime comprised of gaseous compression and (2) a burned-gas regime, which includes high-temperature compression and expansion processes. The time-history of important boundary layer quantities such as gas / wall temperatures, boundary layer thickness, wall heat flux, and relative energy lost at the wall are evaluated through these regimes. During the mild unburned-gas compression, Tcore increases by 30 K and a thermal boundary layer is initiated with thickness δT ~ 200 μm. Wall heat fluxes remain below 6 kW/m2, but corresponds to ~6% energy loss per ms. In the burned-gas regime, Tcore resembles adiabatic flame temperatures, while Twall increases by 16 K. A thermal boundary layer rapidly develops as δT increases from 290 to 730 μm. Energy losses in excess of 25% occur after flame impingement and slowly decay to ~10% at the end of expansion. Measurements also resolve thermal mixing of fresh- and burned gases during expansion, which yield strong temperature reversals in the boundary layer. Findings are compared to canonical environments and demonstrate the transient thermal boundary nature during engine-relevant processes.

Combined scattering-referenced and co-doped aerosol phosphor thermometry using the Ce,Pr:LuAG phosphor

Combined scattering-referenced and co-doped aerosol phosphor thermometry using the Ce,Pr:LuAG phosphor

Visible emission spectra of thermographic phosphors under x-ray excitation

Thermographic phosphors have been employed for temperature sensing in challenging environments, such as on surfaces or within solid samples exposed to dynamic heating, because of the high temporal and spatial resolution that can be achieved using this approach. Typically, UV light sources are employed to induce temperature-sensitive spectral responses from the phosphors. However, it would be beneficial to explore x-rays as an alternate excitation source to facilitate simultaneous x-ray imaging of material deformation and temperature of heated samples and to reduce UV absorption within solid samples being investigated. The phosphors BaMgAl10O17:Eu (BAM), Y2SiO5:Ce, YAG:Dy, La2O2S:Eu, ZnGa2O4:Mn, Mg3F2GeO4:Mn, Gd2O2S:Tb, and ZnO were excited in this study using incident synchrotron x-ray radiation. These materials were chosen to include conventional thermographic phosphors as well as x-ray scintillators (with crossover between these two categories). X-ray-induced thermographic behavior was explored through the measurement of visible spectral response with varying temperature. The incident x-rays were observed to excite the same electronic energy level transitions in these phosphors as UV excitation. Similar shifts in the spectral response of BAM, Y2SiO5:Ce, YAG:Dy, La2O2S:Eu, ZnGa2O4:Mn, Mg3F2GeO4:Mn, and Gd2O2S:Tb were observed when compared to their response to UV excitation found in literature. Some phosphors were observed to thermally quench in the temperature ranges tested here, while the response from others did not rise above background noise levels. This may be attributed to the increased probability of non-radiative energy release from these phosphors due to the high energy of the incident x-rays. These results indicate that x-rays can serve as a viable excitation source for phosphor thermometry.

High temperature phosphor thermometry with YAG: Dy and LED excitation on flexible YSZ ceramic ribbons

High temperature phosphor thermometry with YAG: Dy and LED excitation on flexible YSZ ceramic ribbons

Sources of error for single-shot PMT-based phosphor thermometry in harsh conditions

This study investigates photomultiplier tube (PMT) nonlinearities, relevant for lifetime phosphor thermometry, at various decay times to assess and minimize the impact on temperature measurement accuracy. The focus is single-shot measurements performed in harsh environments where phosphor signal attenuation often is a concern. The sensitivity of decay time measurements to changing phosphorescence intensity is therefore investigated. The experimental results show that for the studied phosphors and detectors, shorter decay times between 20 ns and 6 µs, saturation effects in the PMTs decreased the measured decay time with increasing signal attenuation. For longer phosphorescence decay times, in the millisecond regime, nonlinearity effects led to an increase in the measured decay time with increasing signal attenuation. The specific detector nonlinearity response will vary among detectors, but the introduced methodology for detector analysis is a useful resource for assessing and improving accuracy in lifetime phosphor thermometry measurements.

Characterization of Ce:CSSO, Pr:CSSO, and co-doped Ce,Pr:CSSO phosphors for aerosol phosphor thermometry

The phosphor Ce:Ca3Sc2Si3O12(Ce:CSSO) was recently investigated for aerosol phosphor thermometry (APT) and shown to be capable of temperature imaging up to at least 1400 K. To date, no thorough characterization of the temperature dependent emission properties of the phosphor has been performed up to 1400 K. Additionally, due to limited sensitivity over certain temperature ranges continuous temperature imaging from 300 to 1400 K was not possible. Here, cerium and praseodymium doped into CSSO are investigated to address these limitations. Singly-doped Ce:CSSO and Pr:CSSO, and co-doped Ce,Pr:CSSO phosphor samples were studied. Emission lifetimes and quenching behavior were characterized in a tube furnace for each phosphor. Results from the singly-doped phosphors were used to interpret the co-doped phosphor results. The phosphor characterization data was used to estimate thermometry performance at temperatures relevant to low-temperature ignition studies in engines. The proposed diagnostic uses a combination of co-doped APT, host-referenced APT, and scattering-referenced APT approaches to increase the range over which high-precision temperature measurements can be made. Characterization results include the first reported measurements of luminescence lifetimes for Ce:CSSO and Pr:CSSO at temperatures up to 1400 K, and the highest reported quenching temperature for a phosphor using 4f5d emission (1230 K for Ce:CSSO). Furnace measurements showed a normalized temperature-sensitivity of % K−1 from room temperature to 1400 K for at least one diagnostic approach using the co-doped Ce,Pr:CSSO phosphor. Estimates suggest that the co-doped Ce,Pr:CSSO phosphor is feasible for APT at temperatures ranging from 300 to 925 K and 1030 to at least 1400 K, with better than 40-K single-shot precision. The performance of Ce:CSSO and Ce,Pr:CSSO are similar throughout the investigated temperature range.