LIF Spectra Research Articles

Time-resolved laser-induced fluorescence spectroscopy using CW diode laser for diagnostics of argon-ion velocity distribution near AC-biased electrode.

Controlling the ion velocity in an ion sheath by applying an alternating current (AC) voltage to an electrode and/or a substrate is critical in plasma material processes. To externally control the velocity distribution of incident ions on a substrate, the application of tailored-waveform AC voltages instead of sinusoidal voltages has garnered interest in recent years. In this study, to investigate temporal changes in ion-velocity distributions, we developed a time-resolved laser-induced fluorescence spectroscopy (LIF) system using a continuous-wave diode laser as an excitation-laser source. A time-resolved LIF system entails the capture of temporally continuous and spectrally discrete LIF spectra during an AC voltage cycle. By measuring temporal changes in the LIF signal intensity at various excitation-laser wavelengths, the argon-ion velocity distribution near the electrode following the AC voltage can be characterized. The results of applying sinusoidal, triangular, and rectangular bias waveforms indicate that the LIF measurement scheme proposed herein can be used to investigate the dynamic behavior of ion-velocity distributions controlled by tailored-waveform AC voltages.

On the difficulty of interpreting NO-LIF measurements around 226 nm in confined ammonia flames

This paper addresses how NH3 and NO absorption along the laser axis disrupts NO-LIF measurements made around 225 nm in NH3/O2/N2 premixed flames confined at low pressure (10 kPa). Measurements were performed in 3 flames (equivalence ratio ϕ = 0.87, 1.1 and 1.3) with 24 % N2 dilution. Together with the LIF measurements, single-pass absorption measurements were obtained in all flames as a function of the height above the burner (HAB) and of the wavelength. A significant NH3 absorption of the laser beam is found in the pre-heat zone and flame front of each flame, as well as in the burned gas in the rich flame. In the lean flame, whatever the HAB, an additional significant absorption is due to the NO present in the gas surrounding the flame. Whereas NH3 absorbance only occurs inside the flame under all conditions, NO absorbance is mainly due to the high concentration of NO produced in the lean flame and spread in the entire confined vessel around the flame. From this analysis, relative NO rotational population profiles were recorded by measuring the temporal peak of the LIF signals (prompt-LIF) which were corrected for absorption to account for the available energy at burner's center. NO-LIF thermometry was conducted to determine the temperature in the flames through collecting excitation LIF spectra and performing spectral fitting using a dedicated software (thermo NO-LIF, https://pc2a.univ-lille.fr/thermo-no-lif/). The procedure developed to collect the NO profiles could not be transposed to determine the temperature in the lean flame. Indeed, the attenuation of the laser beam depends on whether the laser is tuned on a “cold” transition (strongly impacted by absorption outside the flame) or on a “hot” transition of NO, little affected. Thus, two tubes (with N2 flushing) were installed inside the vessel along the laser axis and surrounding the flame to suppress the NO absorbance.

Effect of low fuel temperature on combustion deterioration of kerosene swirling spray flames using OH-PLIF

The low fuel inlet temperature poses challenges to the flame stability of aircraft engine combustors. In order to investigate the combustion deterioration of swirl-stabilized kerosene spray flames under conditions of low fuel inlet temperature (T < −16 °C), a comprehensive system was established, comprising a burner commonly used in aircraft engines and a cooling setup. Upon analyzing OH-PLIF images, it becomes evident that sub-zero Celsius temperatures significantly lead to a decrease in OH radical concentration, resulting in a diminished heat release rate. The strongest signals decrease by a minimum of 5 times. Additionally, through the analysis of LIF spectra and detuned images, the differences between OH-LIF and kerosene-LIF are beneficial for recognizing the kerosene particles from the OH-LIF signals at the same time. For atomization assessment, employing the LOG operator blob detection method, it is found that at sub-zero Celsius temperatures, the overall count of fuel LIF particles experiences a slight reduction, while the count of larger particles increases across various air flow rates. This observation highlights an inferior droplet distribution at lower fuel temperatures. The image processing of kerosene LIF particles opens up the possibility for a rapid evaluation of atomization, especially when assessing combustion deterioration in kerosene spray flames through the use of a simple OH-PLIF technique.

Влияние ультрафиолетового света на люминесценцию (700-1000 nm) кристаллов LiF и LiF : ОН, облученных в ядерном реакторе

The emission (700-1000 nm) and absorption (200-800 nm) spectra of LiF and LiF:OH crystals irradiated in a reactor and exposed to ultraviolet light, including those combined with mechanical loading, have been studied. The aim of this work is to study the behavior of laser color centers in these systems. In the 710–825 nm range, diametrically opposite results are observed: high stability of F4-like centers in “pure” LiF and their sharp destruction in LiF:OH crystals. At the same time, in both groups, F3 and F4 centers are destroyed and F2+ and F3- laser centers (825–925 nm) are intensely accumulated. Upon subsequent exposure at room temperature and darkness, spontaneous disintegration of laser centers is observed, accompanied by an increase of concentration of F4-like centers and restoration of the microstructure of irradiated crystals.

RSC: Optically stimulated emission of LiF:Mg, Cu, P - towards 3D optically stimulated luminescence dosimetry

With the introduction of highly conformal treatment modalities, dose verification in 3D is becoming more important than ever for patient-specific quality assurance of radiotherapy. Reusability of 3D dosimeters may be the path to cope with the cost-benefit issues caused by batch-to-batch fluctuations and intense calibration protocols in existing 3D systems. We present the idea of an envisioned (optically stimulated luminescence) OSL-based 3D readout system, which exploits the inherently reusable dosimetry properties of OSL. We provide the emission spectra of the OSL active material LiF:Mg, Cu, P (MCP) for three stimulation wavelengths (460 nm, 532 nm, and 664 nm), and summarize recently published optical characterization results to highlight the requirements of a readout system for an MCP-based dosimeter.

Study on the influence of thermal treatments on the radio-luminescence in LiF:Mg,Cu,P (GR-200A)

Radio-luminescence (RL) spectra of LiF:Mg,Cu,P (GR-200A) were recorded following various annealing treatments with heating temperatures from 240 to 700 °C, with re-annealing at 240 °C and with a combined re-annealing procedure of 20 min at 270 °C followed by 10 min at 240 °C. RL intensity, the position of the maximum RL intensity (λm) and RL spectrum were obviously dependent on the annealing temperature. The thermoluminescence (TL) intensity of the main peak of LiF: Mg, Cu, P can be partially restored, and the RL intensity can be basically increased by re-annealing at 240 °C. The effect of the combined re-annealing on RL is similar to the effect of 240 °C re-annealing, and the RL intensity of a sample with a combined re-annealing was basically less than that with re-annealing at 240 °C. The annealing of 700 °C + 240 °C can be used as an optimized annealing condition for RL measurement by LiF:Mg,Cu,P.

Electronic spectroscopy of the A1̃2A′′/A2̃2A′−X̃2A′ transitions of jet-cooled calcium ethoxide radicals: Vibronic structure of alkaline earth monoalkoxide radicals of C s symmetry

Laser-induced fluorescence/dispersed fluorescence (LIF/DF) and cavity ring-down spectra of the A1̃2A''/A2̃2A'-X̃2A' electronic transition of the calcium ethoxide (CaOC2H5) radical have been obtained under jet-cooled conditions. An essentially constant Ã2-Ã1 energy separation for different vibronic levels is observed in the LIF spectrum, which is attributed to both the spin-orbit (SO) interaction and non-relativistic effects. Electronic transition energies, vibrational frequencies, and spin-vibrational eigenfunctions calculated using the coupled-cluster method, along with results from previous complete active space self-consistent field calculations, have been used to predict the vibronic energy level structure and simulate the recorded LIF/DF spectra. Although the vibrational frequencies and Franck-Condon (FC) factors calculated under the Born-Oppenheimer approximation and the harmonic oscillator approximation reproduce the dominant spectral features well, the inclusion of the pseudo-Jahn-Teller (pJT) and SO interactions, especially those between the A1̃2A″/A2̃2A' and the B̃2A' states, induces additional vibronic transitions and significantly improves the accuracy of the spectral simulations. Notably, the spin-vibronic interactions couple vibronic levels and alter transition intensities. The calculated FC matrix for the A1̃2A''/A2̃2A'-X̃2A' transition contains a number of off-diagonal matrix elements that connect the vibrational ground levels to the levels of the ν8 (CO stretch), ν11 (OCC bending), ν12 (CaO stretch), ν13 (in-plane CaOC bending), and ν21 (out-of-plane CaOC bending) modes, which are used for vibrational assignments. Transitions to the ν21(a″) levels are allowed due to the pJT effect. Furthermore, when LIF transitions to the Ã-state levels of the CaOC-bending modes, ν13 and ν21, are pumped, A1̃2A''/A2̃2A'→X̃2A' transitions to the combination levels of these two modes with the ν8, ν11, and ν12 modes are also observed in the DF spectra due to the Duschinsky mixing. Implications of the present spectroscopic investigation to laser cooling of asymmetric-top molecules are discussed.

Microdosimetric modeling of the relative efficiency of the optical absorption of LiF:Mg,Ti (TLD-100) detectors exposed to 1H and 4He ions

The Microdosimetric d(z) Model was used in combination with simulated microdosimetric specific energy probability distributions for monoenergetic 1H and 4He ions (energy range = 0.1–1000 MeV/n, target size range = 1–2000 nm) to investigate the possibility of modeling the relative efficiency of two optical absorption (OA) bands (4.77 and 5.08 eV) in the OA energy spectra of LiF:Mg,Ti (TLD-100) thermoluminescent detectors. This work represents the first application of the model to a physical system other than thermally- and optically-stimulated luminescence.The 4.77 eV OA trap is populated by electrons liberated during irradiation and its experimental OA relative efficiency was successfully predicted using a target size of 9 nm in the simulations. On the other hand, the model was not able to reproduce the values of the experimentally-observed proton induced OA efficiency above unity for the 5.08 eV OA band associated with the F centers in LiF:Mg,Ti (electron occupied Fluoride vacancy). The F centers are initially present in the LiF lattice but are also created by the irradiation. Since the absence of defect creation by the irradiation is a necessary condition of the microdosimetric model, the discrepancy between the model results for the F band and the experimental data was not unexpected.The calculations for both OA bands are presented as a function of the particle energy and the simulated microdosimetric target size and will be useful in further applications of the model OA relative efficiencies for charged particles.

Multi-line SiO fluorescence imaging in the flame synthesis of silica nanoparticles from SiCl4

Flame synthesis is a powerful and scalable method for generating nanoparticles for a wide range of applications. The chemical interaction of the flame and the precursor combined with the spatial and temporal temperature distribution determine the product properties. For controlled nanoparticle synthesis that can also be scaled to industrial production rates, detailed knowledge of the underlying chemical kinetics and their interaction with the reactive flow is essential. Laser diagnostics has the capability to analyze the process by probing the concentration of important intermediates in shock tubes and reactive flows. The gas-phase synthesis of silica nanoparticles from SiCl 4 in a premixed H 2 /O 2 low-pressure flame reactor is studied by laser-induced fluorescence imaging of SiO mole fractions and temperature. The literature value-based spectroscopy model of SiO used for fitting the LIF spectra are validated based on absorption cross-sections measurements in a shock tube, where SiO is formed under precisely defined conditions (temperature, pressure, mole fraction) using a well-known kinetics mechanism for SiH 4 /CO 2 /Ar decomposition. Based on literature sources, a reaction mechanism is assembled to describe the oxidation of SiCl 4 in the flame, which is then compared to the measured SiO mole fractions distribution to shed light on the current state of the understanding of SiCl 4 combustion chemistry and to direct further refinements.

A Solution for Liquor Recognition Based on PCA-RF and Laser Induced Fluorescence

There are many brands and types of liquor in China. Yet, some merchants use low-quality liquor for high-quality sales, which contains methanol that is harmful to humans. Therefore, the identification of fake liquor is of great significance to human health and brand protection. This paper presents a laser-induced fluorescence (which has very high sensitivity and rapidity) recognition liquor. Specifically, it first sets up a LIF spectrum acquisition system for liquor in the laboratory, uses Principal Component Analysis (PCA) to reduce the dimension of LIF spectral data, and then collects the dimension reduction data for Random Forest (RF) identification. The results show that the average recognition accuracy of RF combined with PCA for liquor is as high as 99.80%. This paper combines PCA-RF with LIF to accurately identify different brands and types of liquor, which provides a new method for the recognition of fake liquor.

Raman spectra of vacancy-containing LiF: Predictions from first principles

The electronic structure and Raman scattering from face-centered cubic LiF with three types of vacancies — an F-center, an F′-center and a vacancy without electrons (vF) — has been calculated by means of hybrid exchange–correlation functional within density functional theory. Our modeling predicts the effective charge of 0.87e,1.50e and 0.10e on the defect, respectively. The F-center induces two in-gap energy levels for two spin states split by 3.4 eV, while the F′-center and the vF induce a single in-gap level 3.8 eV and 2.9 eV below the bottom of conduction band, respectively. The calculated Raman spectra are thoroughly discussed and are found to match well the earlier experimental data. Several peaks are found to shift consistently with the increase of the charge on the vacancy at the rate of about -35cm-1/e.

Single-Shot Temperature Measurements in a Scramjet Combustor Using Thermally Assisted Laser-Induced Fluorescence

The knowledge of the temperature in the flowfield of the scramjet is critical to the understanding of its performance. This study represents the application of an optical diagnostic technique, thermally assisted laser-induced fluorescence, to the temperature measurements in the combustor of a supersonic combustion engine. The experiments were conducted in the T4 shock tunnel using a scramjet model. Experimental data were obtained by focusing a laser beam into the combustor and exciting the OH radical. A detailed numerical model that simulates all radiative and collisional processes of relevance with the appropriate system of differential equations was developed for the analysis of the influence of energy transfer processes on the fluorescence signal. The population distributions achieved with numerical modeling of the LIF process validated the approach proposed to deduce temperatures. By evaluating the scramjet LIF spectra with a full spectral fit, a temperature distribution across the combustor width was obtained. The experimental results were compared with the computational fluid dynamics simulations of the combustion process.

Comparison of optical absorption and thermoluminescence in LiF:Mg, TI (TLD-100) following irradiation by high energy protons and 90Sr/90Y beta rays

The optical absorption (OA) energy spectrum and thermoluminescence (TL) glow curve characteristics of LiF:Mg, Ti (TLD-100) samples following 90Sr/90Y beta ray irradiation and high energy proton irradiation are compared for the first time. The beta ray irradiations were carried at room temperature at a dose rate in LiF of approximately 0.13 Gy min−1. Proton irradiations were carried out at energies of 20 MeV, 40 MeV and 58 MeV with initial stopping powers of 5.5, 3.2 and 2.3 keV μm−1 respectively. Proton escaping the TL detectors had average energies 55.9, 37.1, 14.4 MeV and the corresponding stopping power in LiF 2.43, 3.36, 7.19 keV μm−1 respectively. All proton irradiations were carried out at a dose of 1124 Gy in LiF and the beta irradiations at a dose of 970 Gy in LIF. The OA spectra were deconvoluted with Gaussian Peak Shapes using a commercial “Peak-Fit” non-linear curve fitting program from Jandel Scientific. The Gaussian bands are characterized by the two parameters of band energy and width. The glow curves were deconvoluted using the Ben Gurion University mixed-order kinetics program. In the analysis first-order kinetics glow peak shapes were employed. The major difference between the two spectra is in the optical density of the F band at 5.08 eV; 0.17 compared to an average value of 0.33 following beta and proton irradiation respectively. The relative intensity, protons to betas, of the other OA bands are remarkably similar within the experimental errors and indicate that the traps associated with these OA bands are not created by the irradiation. It is demonstrated that proton irradiation of LiF:Mg, Ti (TLD-100) creates F centers with 75% greater efficiency than 90Sr/90Y beta particles. This finding lends further support to the conclusion that track structure theory is unable to accurately predict proton relative efficiencies in LiF:Mg, Ti The results are also interpreted in the framework the spatially correlated trapping center/luminescent center model for composite peak 5 in LiF:Mg,Ti.

Consistent Franck–Condon modeling of geometry changes for the S0→S1(ππ*) excitation in anthranilic acid: LIF spectroscopy aided by CC2 or TDDFT vibrations

Experimentally-based evaluation of the changes of equilibrium geometry for the S0→S1(ππ*) excitation in anthranilic acid via fitting of Franck–Condon factors is tested for reliability. The modeling is based on the experimental band intensities in the LIF spectrum that are transformed into geometry changes with the aid of the vibrational modes computed using both the CC2 method (the perturbative approximation to CCSD coupled-cluster) and TDDFT(B3LYP). This modeling is a challenging task not only for quantitative spectroscopy, but also for the quantum chemistry calculations, since the adequate reproduction of vibrational modes for the excited state requires a balanced treatment of the π-electronic conjugation and dynamic electron correlation. The most reliable approach (LIF+CC2 Franck–Condon fitting) predicts a dramatic shortening of the O···H distance by 31 ± 1.5 pm, from 1.91 Å in the ground state to 1.60 Å in the excited state. The changes in bond alternation in the H-chelate ring (around 5 pm according to the LIF+CC2 fit) and the shortening of the O···H bond are typically 1 pm larger than modeled with the LIF+TDDFT fit. Changes of valence angles of magnitude around 5° are larger by 0.5°-1.0° according to LIF+CC2 FC fit than the LIF+DFT fit. Consistency of the obtained results shows that the Franck-Condon fitting provides a reliable, experimentally-based approach to evaluation of the excitation-related geometry changes. It has been achieved owing to the quantitatively reliable spectroscopic results and vibrational analysis computed using the quantum chemistry methods that are able to provide correct description of the excited-state vibrational modes involving the intramolecular hydrogen bond.

OPTICALLY STIMULATED LUMINESCENCE OF LiF:Mg,Cu,P POWDER-INFLUENCE OF THERMAL TREATMENT.

It was recently found that LiF:Mg,Cu,P, which is a very well-known thermoluminescent (TL) material, exhibits also quite substantial optically stimulated luminescence (OSL). In the present work a study on the influence of thermal treatment on the LiF:Mg,Cu,P OSL intensity has been performed. The results revealed that the well-known 'gold standard' of 240°C annealing is not appropriate for OSL measurements. The annealing at lower temperatures produced significantly higher OSL intensity. The highest enhancement of the OSL signal, reaching 95% (compared to the initial signal after standard annealing at 240°C/10 min) was obtained after annealing at about 190-200°C/30 min. The OSL emission spectrum of LiF:Mg,Cu,P was also measured and found to be peaked at 360 nm.

Luminescent properties of LiF crystals for fluorescent imaging of nuclear particles tracks

Fluorescent nuclear track detectors (FNTD) based on LiF crystals were used for imaging ionizing particle tracks (including high-energy iron ions), by exploiting photoluminescence of radiation induced F2 and F3+ color centers. The relation between photoluminescence emission spectrum of LiF and quality of FNTD images was investigated. It was found that in the applied experimental conditions, the emission within the green band (530 nm, F3+) is very weak compared to the red band (670 nm, F2). The optimum signal to noise ratio was achieved with setting the measuring window at wavelengths longer than 570 nm. Good quality track images in the green spectral range were obtained only for the highest ionization density: for stopping iron ions.Investigations of the bleaching phenomenon revealed a strong decrease of the PL intensity after long excitation times, in the range of several minutes. The amount of this decrease depends on the used excitation power. In the conditions which were typically applied during FNTD measurements the intensity loss was negligible.

Phonon interaction with OH complexes and products of their radiative decomposition in LiF crystals

This article deal with study of the vibration spectra of hydroxyl ions and radiation-induced molecular complexes with H-bond in LiF:OH crystals. The IR spectra of the crystals were measured at 300, 80 and 10 K temperatures. The low-temperature behavior of the bands in the 3570–3700 cm−1 region indicates that corresponding vibration energy levels are not associated with phonons. It is shown that the broadening of 3730 cm−1 band with increasing temperature due to phonon interactions, namely, resonant scattering of phonons by vibrations of free hydroxyl. The frequencies of the transverse and longitudinal optical modes of phonons take part in the Fermi resonance splitting of the absorption band of molecular complexes with a strong hydrogen bond in the region of 1800–2300 cm−1 in LiF:Mg, OH crystals. It is determined that the narrow bands in the 3400–3700 cm−1 region can appear in the spectrum of LiF:OH without magnesium ions. It was concluded that narrow bands in the 3400–3700 cm−1 region in y-irradiated to a dose of 2.58×104 C/kg at T = 525 K LiF:OH crystals are caused by an associates of two or more hydroxyl ions or by a complexes with a hydrogen bond OH…O or OH…F.

Quantitatively Adequate Calculations of the H-Chelate Ring Distortion upon the S0 → S1(ππ*) Excitation in Internally H-Bonded o-Anthranilic Acid: CC2 Coupled-Cluster versus TDDFT.

The S0 → S1(π → π*) excitation in o-aminobenzoic acid causes strengthening of the N-H···O intramolecular hydrogen bond. The interplay of the hydrogen bond shortening, the hydrogen atom dislocation along the hydrogen bond, and the skeletal relaxation is investigated. These effects often cause the appearance of dual fluorescence from the π-conjugated internally H-bonded molecules, which is traditionally interpreted as the evidence of the excited-state intramolecular proton transfer process: ESPIT. Hence, their quantitative modeling is an important but demanding task for computational photochemistry. Extensive calculations using CC2 method (the perturbative approximation to CCSD coupled-cluster) and TDDFT(B3LYP) were performed with the series of (aug)-cc-pVXZ(X = D,T,Q) basis sets. CC2 predicts remarkable shortening of the O···H distance by 0.273 Å accompanied by the skeleton relaxation that involves considerable distortions of valence angles of the amino group (up to 7.3°) and within the benzene ring (up to 5°). Additionally, moderate changes (<0.046 Å) of the bond alternation in the π-electronic system and the hydrogen atom dislocation along the hydrogen bond (0.043 Å) are predicted. The CC2 method yields 90% of the magnitude of the experimentally based geometry changes, estimated in the earlier studies via Franck-Condon fit to the LIF spectra, while the TDDFT results approach only 65% of the experimental values.

Kinetic simulation of the effect of 3.6 eV and 4.2 eV photon excitation on the optical absorption energy spectrum of 137 Cs gamma irradiated LiF:Mg,Ti (TLD-100)

Abstract The effect of photon excitation on the optical absorption (OA) energy spectrum of LiF:Mg,Ti (TLD-100) following gamma ray irradiation to a dose-level of 2500 Gy are presented. Photon energies of 3.6 eV and 4.2 eV were chosen to selectively excite the trapping centers (TCs) associated with the 3.8 eV and 4.3 eV OA bands. The TCs associated with these OA bands are believed to give rise to the electron-only and electron-hole components of composite glow peak 5 in the thermoluminescence (TL) of TLD-100. Kinetic modeling is shown capable of simulating the changes in the optical density of the OA bands induced by the two photon energies with the same values of the recombination coefficients. This result is in contrast to a previous investigation which could not simulate the OA following both gamma irradiation and photon bleaching with the same values of the recombination coefficients. The results reported herein are consistent with : (i) the interpretation of the e-only and e-h charge configurations giving rise to the 3.8 eV and 4.3 eV OA bands and (ii) the possibility that the recombination processes following gamma irradiation occur not only following thermalization of the electron and hole charge carriers but at higher energies as well.

EPR spectroscopy in LiF:Mg,Cu,P thermoluminescent powder samples irradiated with high gamma doses

Significant changes of the glow curve shape of LiF:Mg,Cu,P have been observed when it is exposed to doses above 50 kGy. In order to clarify one of these changes, i.e., the appearance of a thermoluminescent (TL) peak (the so-called “B” peak) centered above 400 °C, this work investigated the changes induced by γ radiation in the electron paramagnetic resonance (EPR) spectra of LiF:Mg,Cu,P powder used for the production of the MCP-N dosimeters. To achieve this, aliquots were irradiated with 1, 100, 227 and 500 kGy of γ rays (60Co) and preheated at different temperatures up to 500 °C. EPR signals were measured at room and liquid nitrogen temperatures with an X-band spectrometer. Glow curves and TL emission spectra were measured for the same aliquots. EPR spectra were shown to originate mainly from unpaired electrons of Cu2+ ions, occurring in deformed octahedral sites, showing axially symmetric spectroscopic g-factors (g┴ = 2.1937; g║ = 2.0765). Two less intense signals with g-factors equal to 2.008 and 1.989, probably associated with different types of F centers, were observed after irradiation with doses ≥ 100 kGy. The analysis of EPR and TL intensities as a function of radiation doses and preheat temperatures suggested that the creation of the B peak is basically dependent on the electronic trapping states formed by Cu2+ and/or Cu+ ions and the F-related center responsible for the signal with g-factor equal to 1.989. The wavelength of the emitted light (peaked at ~ 360 nm) confirmed that recombination occurs along the same path for both the B peak and the dosimetric peak centered at 220 °C. In contrast to standard TL models, the position of the B peak shifted towards higher temperatures when the dose was increased. These results support the assumption that the origin of the B peak can be explained by localized transitions within spatially correlated defect clusters assembling Cu2+ and Mg2+ ions together with F-related centers.