Thermographic Phosphor Thermometry Research Articles

Data recovery of 2D lifetime-based phosphor thermometry using deep neural networks

Thermographic phosphor (TP) thermometry has been widely used as one of the newly developed non-contact surface temperature measurement methods. However, temperature information is frequently lost locally because chemical bonding coatings are easily damaged during the measurement. This limits its application, such as in the case of jet impact, high-speed motion, high vibration, etc. We proposed to use of deep neural networks (DNNs) as a tool for recovering lost data. In this study, we captured the dynamic two-dimensional (2D) temperature field of jet impingement cooling a high temperature plate by TP thermometry. Different parts of the temperature information, including jet impact area and non-impact area, were then removed to assume the coating was damaged. A prediction model was established by the DNNs using the 2D space and time coordinates as the input dataset and using the temperature information corresponding to the coordinates as the output dataset. The removed temperature information was then recovered using the developed regression model and compared with the raw temperature field to evaluate predicted results. The results showed that the removed data can be successfully recovered using the established DNN prediction model, in which the predicted accuracy was greater than 94.94%. While in the central and the boundary area of the jet, the model has a relatively poor performance, which is mainly due to the large temperature gradients. These results indicate that the established DNN model can be used to recover the lost temperature information but it is limited for applications in regions with drastic temperature changes.

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.

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.

Experimental study on flow characteristics and heat transfer of an oscillating jet in a cross flow

In the present paper, flow characteristics of an oscillating jet in a cross-flow (OJICF) emitted from a double feedback fluidic oscillator were investigated. The results were compared with a steady jet in a cross-flow (JICF) from a jet nozzle with length and diameter equal to those of the fluidic oscillator. Smoke visualization in a low-speed wind tunnel was used. The measurements were done in the symmetry plane with 3 cross sections for 4 different blowing ratios (BR) of 1 to 3.33. The OJICF shows high potential to enhance the effectiveness of film cooling since it penetrates to a lesser height and leads to considerable spanwise penetration. Then, heat transfer behaviors of an impinging OJICF (IOJICF) and impinging JICF (IJICF) were compared via thermographic phosphor thermometry (TPT). The cross-flow Reynolds number based on the hydraulic diameter of the jet exit and cross-flow velocity was varied between 510 and 2,700, and the spacing between the jet and target surface was 3 times the jet throat's hydraulic diameter. The results show that for the IOJICF, heat transfer is dominated by the cross flow, and changing the BR does not have a significant effect. However, the IJICF promotes heat transfer around 2 times more than the IOJICF, and the more the BR is, the greater the Nu number. Therefore, the OJICF could be applied for film cooling rather than impinging applications.

Acquisition of kHz-frequency two-dimensional surface temperature field using phosphor thermometry and proper orthogonal decomposition assisted long short-term memory neural networks

A reconstruction technique of kHz time-resolved two-dimensional (2D) surface temperature field was achieved with the discrete point measurements and low sampling rate 2D thermographic phosphor (TP) thermometry measurements using a long short-term memory (LSTM) based artificial intelligence framework. The 2D surface temperature field of a 350 °C plate with a 2.5 Hz swing cooling jet was measured using TP thermometry at a sampling rate of 20 Hz. At the same time, high-frequency thermocouples with a sampling rate of 1 kHz were recorded for the construction of LSTM neural networks training and for validation. The 20 Hz 2D surface temperature field was analyzed with proper orthogonal decomposition to acquire the energy modes and model coefficients. The mode coefficients are then trained with the discrete but high-frequency time-resolved temperature information from the thermocouple by LSTM to acquire the time-resolved mode coefficients. Finally, the high-frequency time-resolved 2D surface temperature field is obtained by reconstructing modes and the time-resolved coefficients. The reconstructed result shows that the current technique can obtain high time-resolved and spatially resolved 2D surface temperature fields very well.

A direct method for the simultaneous characterization of thermal diffusivities of a bi-layer material consisting of a thin coating deposited on a substrate

This work presents a method dedicated to the simultaneous identification of the thermal diffusivities of coatings or thin film materials. To ensure non-destructive thermal characterization of the coating, the present method also implies the identification of the substrate thermal properties, which may be orthotropic. The estimation of thermal diffusivities is based on the resolution of an inverse problem by minimizing the quadratic difference between the response of a 3D semi-analytical model and the measurements resulting from a single ‘3D flash method’ type experiment, using a stochastic based optimization algorithm. A unique non-intrusive test, that consists in recording the temperature change cartography on one face of the sample by means of an infrared camera, is required. The evolution of the temperatures within the material is generated by a non-uniform and almost instantaneous excitation imposed by a CO2 laser on the measured face. The difficulties related to the control of the excitation, in terms of the distribution of the imposed flux or the energy absorbed by the material, are overcome by estimating the parameters associated to the excitation simultaneously with the thermal diffusivities. The developed method is applied to estimate the thermal diffusivity of a coating used in thermographic phosphor thermometry to measure wall surface temperatures and heat fluxes in combustion environments. The method is first evaluated on simulated data as a function of the measuring/excitation face in order to ensure the feasibility, the robustness and accuracy of the current method and to establish the best experimental configuration. Experimental results are then exploited and the estimation results are compared with other methods results.

Experimental and numerical study on flow characteristics and heat transfer of an oscillating jet in a channel

A fluidic oscillator can produce self-induced and self-sustaining oscillating jet by fluid supply without moving parts. This device has attracted research interest in heat and mass transfer enhancement in recent years. In the current study, a double-feedback fluidic oscillator was numerically investigated based on three-dimensional unsteady Reynolds-averaged Navier-Stokes equations (3D-URANS) while the operating fluid is an incompressible flow. Then, the results were validated with experimental data by two-dimensional time-resolved particle image velocimetry (2D-TR-PIV) and thermographic phosphor thermometry (TPT) for the velocity and temperature field, respectively. A grid sensitivity study was done by comparison of instantaneous and time-averaged flow fields. Additionally, the proper orthogonal decomposition (POD) method was used to find the phase information of the oscillating jet, and fast Fourier transform (FFT) analysis was used to find the frequency of the oscillating jet to validate the numerical results. The effect of the working fluid was also studied. Finally, in order to determine the effect of the Reynolds number on heat transfer enhancement, the Q-criterion was calculated to provide detailed insight into the oscillating mechanism. The results show that the non-dimensional frequency of oscillation is independent of either the working fluid or mass flow rate. Additionally, for a given fluid, increasing Re causes strong vortices and increases the frequency of oscillation. However, the convection heat transfer did not change significantly when varying the mass flow rate because the convection velocity of vortices increases as the mass flow rate is enhanced. A comparison with a free jet reveals that the oscillating jet in a channel is useful in terms of covering a larger area.

Measurement of three-dimensional flow structure and transient heat transfer on curved surface impinged by round jet

In this study, the transient heat transfer characteristics of a circular cylinder surface cooled by an impinging air jet were measured through thermographic phosphor thermometry. Time-resolved surface temperature fields were visualized under constant heat flux conditions. After the jet impingement on the circular cylinder, the curved three-dimensional (3D) wall jet developed toward both spanwise and streamwise directions, followed by most of the fluid moving along the curved surface due to the Coanda effect. Therefore, the high heat transfer region was elongated toward the streamwise direction. The impinging angle was established to be a dominant factor in heat transfer characteristics. The heat transfer was improved with an increase in the impinging angle, as the cooling area expanded toward the streamwise direction. To discuss the transient heat transfer characteristics, time-resolved two-dimensional Nusselt number distributions were obtained according to the varied impinging angles and Reynolds numbers. The secondary peak of heat transfer was not clearly observed due to the stabilizing effect of curvature on the wall jet. To understand the heat transfer phenomenon, the 3D flow structures of the jet on the curved surface were obtained using time-resolved volumetric particle tracking velocimetry (PTV). The velocity vectors and streamwise vortices were visualized according to the impinging angle and analyzed in three-dimensions. The 3D curved wall jet possessed a big counter-rotating streamwise vortex structure in the upper region of the attached wall jet on the cylinder wall. With an increase in the impingement angle, the streamwise vortex developed longer at the same Reynolds number. The 3D flow structure and heat transfer distribution were found to demonstrate similar tendencies.

Experimental study on heat transfer and flow structures of feedback-free sweeping jet impinging on a flat surface

This study examined the flow structure and heat transfer characteristics of a sweeping jet generated from a feedback-free fluidic oscillator. A feedback-free sweeping jet (FFSJ) was proposed to enhance impinging heat transfer with a large jet-to-wall spacing. The surface temperature field of a plate cooled by a jet impingement was measured by thermographic phosphor thermometry using the decay-slope method according to a range of Reynolds number (Re) and various jet-to-wall spacing (Z/dh). The results were compared with those of a square jet (SJ) and conventional feedback sweeping jets (FSJ). Time-resolved particle image velocimetry, proper orthogonal decomposition analysis, and smoke visualization were conducted to determine the external flow characteristics of the FFSJ. The FFSJ oscillated with the 7dh wavelength. The frequency and sweeping angle were higher and smaller, respectively, that of the FSJ. The heat transfer performance of an impinging FFSJ was superior to that of an SJ when the jet-to-wall spacing was lower than 5dh. The peak Nusselt number increased with increasing Reynolds number. At a fixed Reynolds number of 32,000, the local heat transfer performance of the FFSJ was superior to that of the FSJ. As the jet-to-wall spacing increased, the effect of heat transfer enhancement also increased. At Z/dh = 8, the peak Nusselt number of the SJ surpassed the FFSJ, but the integrated heat transfer rate of an FFSJ was comparable to that of an SJ.

An experimental study on the flow and heat transfer of an impinging synthetic jet

This study experimentally investigated the combined effects of the wall temperature (Tw0) and the orifice-to-wall distance (H/D) on the flow and heat transfer characteristics of an impinging synthetic jet. Thermographic phosphor thermometry (TPT) was used to measure the wall surface temperature, and the quantitative flow velocity was obtained using time-resolved particle image velocimetry (PIV). A cavity-diaphragm actuator was employed to generate a round synthetic jet to impinge onto a heated wall that was coated with Mg4FGeO6:Mn (MFG) for use as a temperature sensor. Three orifice-to-wall distances (H/D = 10, 15, and 20) and three wall temperatures (Tw0 = 60 °C, 90 °C, and 120 °C) were tested for comparison, whereas the the operating conditions of the incident synthetic jet were kept constant. It was found that the maximum temperature drop at the stagnation point could reach approximately 50°C although the orifice-to-wall distance was relatively large in this study, which indicated a good cooling performance of the synthetic jet. The penetration of the wall shear layer played an important role on the cooling performance of the impinging synthetic jet. For a heated wall with high Tw0, the enhanced buoyancy and thermal boundary layer resulted in the formation of a strong wall shear layer, which was more difficult for the impinging synthetic jet to affect or penetrate. For a large H/D, the vortex rings of the synthetic jet lose coherence completely before impacting the wall. Thus, they have no ability to penetrate the wall’s shear layer to interact with it directly. As a result, the cooling performance of the impinging synthetic jet gradually decreased as both Tw0 and H/D increased. In particular, the maximum cooling effect by the synthetic jet impingement can achieve 64% of the theoretical maximum.

Effect of frost on phosphorescence for thermographic phosphor thermometry

In this study, we analyzed phosphorescence lifetime and its accuracy by growing frost for thermographic phosphor thermometry in a low-temperature environment. Mg4FGeO6:Mn particles were coated on an aluminum plate and excited with a UV-LED to obtain phosphorescence signals. The surface temperature was maintained at −20, −15, −10 °C, and the phosphorescence signal was acquired as the frost grew for 3700 s. The lifetime was calculated and compared with the calibration curve under no-frost conditions. The error of the measured lifetime was within 0.7% of that in the no-frost conditions. A 2D surface temperature profile of the target plate was successfully obtained with the frost formation.

“Oxygen quenching” in Eu-based thermographic phosphors: Mechanism and potential application in oxygen/pressure sensing

The effect of ambient oxygen concentration on thermographic phosphor thermometry was investigated to uncover the “oxygen quenching” mechanism of Eu-based phosphors using a lifetime-based measurement system. The phosphors being studied were the Eu doped yttria stabilized zirconias (YSZs) with Y3+ concentrations of 0, 8, 12 and 57mol%, having monoclinic, tetragonal, cubic and δ crystalline lattice, respectively. To vary the ambient oxygen concentration, three different gas phases (air, oxygen and nitrogen with methane) were used. It was found that the phosphorescent lifetimes and intensities of all four phosphors were sensitive to the ambient oxygen concentration, while the reference phosphor, Y2SiO5:Eu, was not influenced. The “oxygen quenching” phenomenon observed in Eu-doped YSZs was attributed to the oxygen vacancies in the phosphors. In addition, the four YSZ:Eu phosphors exhibited different sensitivity to ambient oxygen concentration. The oxygen sensitivity was found to be closely related to the site symmetry of Eu3+, which was previously determined by the phosphorescent spectra. The site symmetry of Eu3+ strongly affected the charge-transfer states and therefore determined the non-radiative decay rate. The current findings provided guidance for the phosphor selection and sensor design for oxygen/pressure sensing in high-temperature environment.

“Simultaneous measurement of flame impingement and piston surface temperatures in an optically accessible spark ignition engine”

This paper shows the results of spatially resolved temperature measurements of the piston surface of an optically accessible direct injection spark ignition engine during flame impingement. High-speed thermographic phosphor thermometry (TPT), using Gd3Ga5O12:Cr,Ce, and planar laser-induced fluorescence of the hydroxyl radical (OH-PLIF) were used to investigate the temperature increase and the time and position of flame impingement at the piston surface. Measurements were conducted at two operating cases and showed heating rates of up to 16,000 K/s. The OH-PLIF measurements were used to localize flame impingement and calculate conditioned statistics of the temperature profiles. The TPT coating was characterized and its influence on the temperature measurements evaluated.

Two-dimensional thermographic phosphor thermometry in a cryogenic environment

In this study, lifetime-based thermographic phosphor thermometry was developed for 2D temperature measurements in a cryogenic temperature environment. A chamber was set up to provide such an environment with temperatures of 300–110 K and accuracy of ±3.5 K. Mg4FGeO6:Mn was used as a sensor material, which was excited by a pulsed UV LED. A high-speed camera with a frequency of 8000 Hz was used for the phosphor thermometry. Calibration was performed at temperatures ranging from 110 to 290 K. The calibration results clearly show variation in the lifetime at different temperatures, and the calibration error is within 1.7%. This measurement is demonstrated in a 2D temperature measurement of an aluminum plate with a heater for both steady and unsteady heat transfer conditions. The measurement results were compared with thermocouple measurements to validate the method.

Effect of surface moisture on chemically bonded phosphor for thermographic phosphor thermometry

This study examined the effect of surface moisture on the calibration lifetime in chemically bonded phosphor paint preparation. Mg4FGeO6:Mn was used as a sensor material, which was excited by a pulsed UV LED. A high-speed camera with a frequency of 8000 Hz was used to conduct phosphor thermometry. Five samples with different degrees of surface moisture were selected during the preparation process, and each sample was calibrated 40 times at room temperature. A conventional post-processing method was used to acquire the phosphorescent lifetime for different samples with a 4 × 4-pixel interrogation window. The measurement error and paint uniformity were also studied. The results showed that there was no obvious phosphorescence boundary between the wet parts and dry parts of phosphor paint. The lifetime increased by about 0.0345% per hour during the preparation process, showing the degree of surface moisture had almost no influence on the lifetime measurement. The lifetime changed only after annealing treatment. There was also no effect on the measurement error and uniformity. These results provide a reference for developing a real-time measurement method using thermographic phosphor thermometry. This study also provides a feasible basis for chemically bonded phosphor thermometry applications in humid and low-temperature environments.

Transient temperature field and heat transfer measurement of oblique jet impingement by thermographic phosphor

The transient heat transfer characteristics of a hot plate cooled by an oblique jet were investigated by thermographic phosphor thermometry. The initial surface temperature was 360°C, and 2D instantaneous temperature fields were measured with 0.1-s time intervals for a jet Reynolds number of 3500. The distance from the nozzle to the surface and the angle of impingement were varied for measurements. Manganese-activated magnesium fluorogermanate (Mg4FGeO6:Mn) was used as a thermographic phosphor, and a pulsed UV-LED with a 385-nm wavelength was used for the light source. A CMOS high-speed camera acquired phosphorescence images at 4000framespersecond. The decay-slope method was used for calibration, and the uncertainty in the temperature measurement was less than ±3% for the wide temperature range of 130–530°C. A 1D semi-infinite solid model was used to obtain the local heat transfer coefficient. The transient heat transfer is almost two times greater than the steady-state value. The maximum heat transfer coefficient occurred at the stagnation point, and a secondary peak appeared at high impinging angle. When the distance from the nozzle to plate is fixed, the air jet with high impinging angle shows better cooling performance. Flow visualization and time-resolved PIV measurements reveal that the secondary heat transfer peak is associated with unsteady vortex at the beginning of the wall jet.

Thermographic phosphor thermometry in transient combustion: A theoretical study of heat transfer and accuracy

Thermographic phosphors (TPs) are used in combustion environments to study wall surface temperatures and heat fluxes. Recently they are also applied in unsteady environments like internal combustion engines to study the heat transfer to walls. The present study investigates theoretically some related effects leading to limitations of the method and thus trying to help experimenters to choose proper conditions for their experiments. The influence of absorptivity and film thickness is studied first. Then the unsteady heat flux of a surrounding gas phase is investigated as a function of film thickness and conductivity, including the effect on the temperatures which would be measured using TPs. The errors in temperature measurements and time resolution are investigated for typical cases. Finally the relation between the surface temperature and film thickness is investigated for combinations of two base materials (quartz and steel) coated with layers of Mg2SiO4 or SiO2, as representatives for TP host materials. It is seen that the maximum surface temperature is influenced in unsteady heat transfer processes even by relatively thin layers.

Two-dimensional thermographic phosphor thermometry using a CMOS high speed camera system

In the present study, a CMOS high speed camera system was employed for two-dimensional thermographic phosphor thermometry. By the pixelwise evaluation of the luminescence lifetimes, a temperature map of a phosphor layer can be obtained. Using spatially and temporally isothermal conditions in a tube furnace, a temperature lifetime characteristic was determined for the phosphor Mg4FGeO6: Mn and was compared with data obtained by point measurements using a photomultiplier tube. Both, the pixel-to-pixel and the shot-to-shot standard deviation were evaluated at different temperatures. Non-linearities and pixel-to-pixel inhomogeneities of the CMOS chip were characterised and corrected employing a homogeneous light source.

On the design of phosphors for high-temperature thermometry

The temperature-dependent luminescence of certain thermographic phosphors has been used in surface thermometry for a number of years. Of the two practical methods by which temperature can be deduced from the emission [Heyes, A.L., Thermographic Phosphor Thermometry— Physical Principles and Measurement Capability, In: C.H. Sieverding, J.-F. Brouckaert (Eds.), VKI Lecture Series on Advanced Measurement Techniques for Aero and Stationary Gas Turbines. 2004, von Karman Institute for Fluid Dynamics, Brussels, (Vol. Lecture Series 2004–04)], the one considered herein relies on thermally activated non-radiative transitions from the excited to ground state making the decay rate in luminescence temperature dependent. The time constant of the exponential decay in luminescence can then be used to derive the temperature. The authors and co-workers have been working for some years now on the application of this method for condition monitoring and non-destruction evaluation in the hot sections of gas turbines. Turbine entry temperature is linked to efficiency and thereby to CO 2 emissions so that there is a clear imperative to increase it. Current entry temperatures exceed the melting points of the metals from which local components such as combustion liners, nozzle guide vanes and turbine blades are made. Thermal management of these components is therefore critical to the operation of the engine and by implication sensors and instrumentation are required to aid the design of insulation and cooling schemes and to monitor their performance in service. Thermographic phosphors typically consisting of a ceramic host (e.g. YAG) with a rare-earth dopant are excellent candidates. These materials are stable at the required temperatures and the temperature dependence of their luminescence can provide a dynamic range that matches the expected environment. In this paper, the physics of the multi-phonon non-radiative decay process are reviewed and used to construct a simple design model for thermographic phosphors. Comparison with experimental data shows general agreement but there are several anomalous cases. These are reviewed and alternative thermal quenching mechanisms considered.

An algorithm for the characterisation of multi-exponential decay curves

An algorithm for the non-ambiguous reduction of multi-exponentially decaying luminescence signals to scalar lifetimes is described and characterised. Whereas this investigation stems from the research of thermographic phosphor thermometry, the technique can also be useful for the analysis of various other decay phenomena. Thermographic phosphors are activator-doped ceramics, whose phosphorescence decay characteristics depend on their temperature. Although the underlying energy transfer processes of the generally multi-exponential phosphorescence decay are not understood in detail, this property can be exploited for remote thermometry. Thereby, the temperature measurement is converted to the measurement of a phosphorescence lifetime evaluated by the approximation of a single-exponential term within a fitting window where mono-exponential decay characteristics prevail. In contrast to multi-exponential approaches, ambiguity due to the attribution of various exponential terms is eliminated provided that the fitting window is the same for the evaluation of all measurement data obtained at unknown temperatures and all temperature-referenced calibration data. In order to achieve this, an iterative algorithm was applied that selects a fitting window dependent on the decay waveform itself. This algorithm was characterised in detail using data detected for two different thermographic phosphors ( Mg 4 FGeO 6 : Mn and Y 2 O 3 : Eu ), at two different temperatures each. Compared to less elaborate routines applying a predefined fitting window depending on an ambiguous setting of the phosphorescence signal's detection length, the evaluation-induced systematic error of temperature determination could be reduced by a factor of 10 3 at similar precision.