Fábio Roberto Batista

Bio: Fábio Roberto Batista is an academic researcher from Federal University of Paraná. The author has contributed to research in topics: Luminescence & Time domain. The author has an hindex of 1, co-authored 2 publications receiving 6 citations.

Photomultiplier nonlinear response in time-domain laser-induced luminescence spectroscopy

Abstract: A new procedure to find the limiting range of the photomultiplier linear response of a low-cost, digital oscilloscope-based time-resolved laser-induced luminescence spectrometer (TRLS), is presented. A systematic investigation on the instrument response function with different signal input terminations, and the relationship between the luminescence intensity reaching the photomultiplier and the measured decay time are described. These investigations establish that setting the maximum intensity of the luminescence signal below 0.3V guarantees, for signal input terminations equal or higher than 99.7 ohm, a linear photomultiplier response.

Time-resolved luminescence studies in hydrogen uranyl phosphate intercalated with amines

Abstract: Time-resolved luminescence decays of intercalated compounds of hydrogen uranyl phosphate (HUP) with p-toluidinium (HUPPT), benzylaminium (HUPBZ), α–methylbenzylaminium (HUPMBZ) and hydroxylaminium (HUPHAM) were studied. The prepared compounds belong to the tetragonal P4/ncc space group and showed 00 l reflections shifted to lower angles relative to HUP, indicating that the intercalation increases the c parameter of the unit cell. The luminescence decays of the compounds with 100% of intercalation ratio (HUPHAM and HUPBZ) were analyzed by Global Analysis, assuming Lianos’ stretched exponential as the model function, which can be applied to compounds with restricted geometry and mobile donor and quencher molecules. It was remarkable that the luminescence decays showed that the quenching of the emission of the uranyl ions by the intercalated protonated amines is not restricted by low dimensionality of the host uranyl phosphate, and that a diffusion mechanism occurs. Benzylaminium cation efficiently quenches the excited energy of the uranyl ions at close distance, but the long-range and long-lifetime quenching is hindered. A different situation is found in the case of the small hydroxylaminium cation, where the long distance diffusion of the species is fast, playing an important role in the quenching of the excited uranyl ions at longer times.

Performance of photomultipliers in the context of laser-induced incandescence.

Abstract: Photomultiplier tubes (PMTs) are widely used as detectors for laser-induced incandescence (LII), a diagnostics method for gas-borne particles that requires signal detection over a large dynamic range with nanosecond time resolution around the signal peak. Especially when more than one PMT is used (i.e., for pyrometric temperature measurements) even small deviations from the linear detector response can lead to significant errors. Reasons for non-linearity observed in other PMT measurement techniques are summarized and strategies to identify non-linear PMT operation in LII are outlined. To quantify the influence of the non-linear behavior, experiments at similar light levels as those encountered in LII measurements are carried out, and errors propagated in two-color pyrometry-derived temperatures are determined. As light sources, a calibrated broadband light source and light-emitting diodes (LEDs), centered at the bandpass filter wavelengths of the LII detectors, were used. The LEDs were operated in continuous and pulsed (<300 ns) mode, respectively, to simulate DC background radiation (e.g., from sooting flames) and similar pulsed signal traces as in typical LII measurements. A measured linearity deviation of up to 10% could bias the temperature determination by several hundred Kelvin. Guidelines are given for the design and the operation of LII setups, which allow users to identify and prevent errors.

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

Abstract: 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.

Detector calibration and measurement issues in multi-color time-resolved laser-induced incandescence

Abstract: Time-resolved laser-induced incandescence is used to infer the size distribution of gas-borne nanoparticles from time-resolved pyrometric measurements of the particle temperature after pulsed laser heating. The method is highly sensitive to aspects of the measurement strategy that are often not considered by practitioners, which often lead to discrepancies between measurements carried out under nominally identical conditions. This paper therefore presents a well-documented calibration procedure for LII systems and quantifies the uncertainty in pyrometric temperatures introduced by this procedure. Calibration steps include corrections for: (1) signal baseline, (2) variable transmission through optical components, and (3) detector characteristics (i.e., gain and spectral sensitivity). Candidate light sources are assessed for their suitability as a calibration reference and the uncertainty in calculated calibration factors is determined. The error analysis is demonstrated using LII measurements made on a sooting laminar diffusion flame. We present results for temperature traces of laser-heated particles determined using two- and multi-color detection techniques and discuss the temperature differences for various combinations of spectral detection channels. We also summarize measurement artifacts that could bias the LII signal processing and present strategies for error identification and prevention.

Improved measurement precision in decay time-based phosphor thermometry

Abstract: This study comprises a continuation of the previous efforts of the authors to characterize different sources of errors in phosphor thermometry based on the determination of luminescence decays from thermographic phosphors. Whereas earlier investigations focused on point detectors utilizing different sensor technology, this work presents a comparison of four PMTs that are identical in terms of their product type. These detectors are supposedly identical, but the investigations revealed that their response is strictly individual. This study also shows a linear excitation energy dependence for the decay time of cadmium tungstate (CdWO4), the phosphor being used in this work. In addition, the potential influence of the intense and short fluorescence peak preceding the weaker and longer exponential decay in some phosphor materials was investigated using the electrical signal gating capability of the PMT. Finally, the evaluated decay time also appeared to be affected by the oscilloscope settings used when recording the phosphorescence signals. The presented results indicate that all operating parameters from the calibration measurement need to be rigorously reproduced in order to avoid systematic temperature errors in phosphor thermometry experiments that are based on reproducible measurements of the decay time. These results should be of more general interest also outside the phosphor community as the findings, presented herein, in principal concern all kinds of measurements that are dependent on reproducible measurements of signal shapes or time transients.

Spectroscopic markers for uranium(VI) phosphates. Part II: the use of time-resolved photoluminescence

Abstract: Detection of uranium hydrates that are relevant for environmental sustainability and adsorption at surfaces is effected using time-resolved photoluminescence spectroscopy (TRPL) with simultaneous lifetime and spectral acquisitions. The study is the second paper devoted to this topic (part I: Faulques et al. RSC Adv., 2015, 5, 71219) and focuses on photoluminescence (PL) phenomena. When a temporal dimension is added, the TRPL technique surpasses, via PL decay analysis, steady-state approaches for discriminating minerals with very similar optical and PL spectra. Further, estimates of quantum yields and nonradiative lifetimes can be given. The results are pertinent in the context of remote sensing of parent hazardous uranyl compounds in the environment.