Heating Rate Method Research Articles

A Study toward the Model Independence of Various Heating Rates Method in Thermoluminescence Glow Curve Analysis

This study analyzes thermoluminescence (TL) glow curves simulated in general order kinetics (GOK), one trap one recombination center (OTOR), and non‐interactive multi‐trap system (NMTS) models using various heating rates (VHR) method in linear heating scheme to extract the activation energy. A theoretical analysis to determine activation energy from TL curves using OTOR and NMTS models in an iterative manner, where the TL intensity is determined by using the Lambert‐W function, is proposed with its limitations. It is established that the activation energies in OTOR and NMTS models consist of the relevant GOK term and a respective correction term. Systematic analysis is carried out to study the improvement of the accuracy of activation energy derived from OTOR and NMTS model TL curves over the GOK model calculation. A quantitative analysis of the quasi‐equilibrium (QE) approximations is carried out for choosing appropriate system parameters. The validity of QE conditions are determined by studying variations of full width at half maximum as well as area under the curve as a function of heating rate. The present method is applied on some experimental data to estimate activation energies. This investigation reveals that the activation energy derived in VHR method has negligible dependence on the underlying theoretical models, i.e., the activation energy derived from GOK model calculation is significantly accurate for experimental scenario.

Kinetics of the thermal decomposition of thermally reduced graphene oxide treated with a pulsed high-frequency discharge in hydrogen atmosphere

Thermal stability and the kinetics of thermal decomposition of the thermally reduced graphene oxide (TRGO) treated by a pulsed high-frequency discharge in a hydrogen atmosphere have been studied. The modified Hummers method was used for obtaining the initial graphite oxide from graphite powder. Thermal exfoliation of the graphene oxide powder has been done in vacuum conditions with a heating rate of 5–7 degrees per minute to a temperature of 300 °С. TRGO has been treated by pulsed high-frequency discharge in a hydrogen atmosphere for partial graphene hydrogenation (chemical addition of atomic hydrogen) that leads to structural changes in the carbon planes and formation of C–H sp3 bonds. The thermogravimetry analysis measurements of the mass loss have been carried from room temperature to 1000 °C in a nitrogen atmosphere with a nitrogen flow rate of 20 mL/min and different heating rates: 50, 75 100, 125, 150, and 200 K/min, respectively. Kissinger’s multiple heating rate method has been used to determine the activation energy for decomposing substances. Activation energies Ea1, Ea2, and Ea3 equal 28, 50, and 148 kJ/mol, respectively, have been compared with the energies of the activation of thermal defunctionalization of multiwalled carbon nanotubes (MWCNTs). The activation energy Ea3 = 148 kJ/mol is close to that of the thermal decomposition of anhydride functional groups in MWCNT. The value of Ea2 = 50 kJ/mol indicates the presence of the keto and hydroxy acid’s function groups on TRGO. Activation energy Ea1 = 28 kJ/mol related with all other groups including the lighter C–H bonds that destructed due to dehydrogenation of the TRGO. Obtained experimental results are useful for further proposing the kinetic model of the mechanism of the most probable reaction of TRGO decomposition.

Qualifying the cathode aging process for storage life prediction for primary AgO-Zn batteries

AgO-Zn batteries are widely recognized for their high energy density, specific capacity, and safety features. Especially the AgO-Zn reserve battery, which possesses good storage stability to better adapt to the application requirements of long-term storage, is considered an ideal candidate for applications in military, aerospace, and other fields. However, since there are only a few studies on the decomposition kinetic of the cathode for the AgO-Zn reserve battery, further in-depth research is needed on the aging mechanism. Herein, we conduct a comprehensive investigation of the aging behavior of the cathode in commercial AgO-Zn reserve batteries. The physicochemical properties of the cathodes with different storage years are characterized by multiple methods, including phase composition, surface morphology, and thermal behaviors. The evolution of structure and performance for the cathodes with storage time and their impact on the electrical performance of AgO-Zn batteries are studied. In addition, a multiple heating rate method is performed to determine the thermal decomposition kinetics of the cathode. Based on the obtained kinetic parameters, a model for the decomposition of the AgO in the cathode is developed, enabling the estimation of theoretical storage time for achieving the cathode with the same retention rate as actual storage in a shortened time by accelerated aging. Validation studies comparing accelerated aging results with real-time aging under natural conditions are further performed to assess the reliability of the accelerated aging model. This research provides insights into the aging mechanisms of cathode for AgO-Zn batteries and offers a systematic approach for the accelerated aging test, paving the way for the development of the prediction of battery performance and lifespan.

Luminescence properties of Ce and Be-doped CaAl12O19 for dosimetric and light-emitting applications

In this study, we reported the sol-gel production of cerium (Ce) and beryllium (Be)-doped calcium aluminate (CaAl12O19) and its luminescence properties for optically stimulated luminescence (OSL) dosimetry and light-emitting applications. Structural, morphological and elemental characteristics of the samples were examined by x-ray diffraction (XRD), Scanning electron microscope (SEM)/energy dispersive spectrum (EDS), x-ray fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) techniques. The maximum OSL intensity was achieved with 0.5 and 2% mol concentrations of Ce and Be dopants, respectively. We investigated the OSL and thermoluminescence (TL) properties of Ce and Be-doped CaAl12O19 by measuring energy storage for 24 h, dose-response in the range of 0.1 and 20 Gy, and reusability of the samples for 15 cycles. Photometric properties of the phosphors were investigated by evaluation of CIE chromaticity coordinate (x, y), CCT, and colour purity using its corresponding photoluminescence (PL) emission spectra. We also applied computerized glow curve deconvolution (CGCD), various heating rate methods, and the Tm-Tstop procedure to determine the trap localizations associated with the TL glow curve. The results of this study point out that CaAl12O19 crystals have the potential to be used as OSL dosimetry when appropriate dopants are used. This study may offer new possibilities in radiation dose detection and monitoring.

Theoretical understanding of defects-driven mechanoluminescence for Pr3+-doped NaNbO3/LiNbO3 heterojunctions

Mechanoluminescence (ML), which involves the emission of light under mechanical stimuli, shows great potential in various applications such as sensing, imaging, and energy harvesting. Current research suggests that the luminescence mechanism of ML is typically connected to specific defects present within the material. In this study, we focus on the investigation of ML defects in Pr3+-doped NaNbO3/LiNbO3 heterojunctions, employing a combination of experimental and theoretical approaches. Through experimental analysis, we confirmed the presence of the heterojunction and its influence on ML intensity, and the optimal doping ratio for the heterojunction in ML was established. Furthermore, we examined the influence of varying Pr3+ doping concentrations on ML behavior and a proof-of-concept was demonstrated using the X-rays charged heterostructural phosphor as a stress sensor for biological applications. The position and concentration of internal defects in the ML material were scrutinized through thermoluminescence tests employing the variable heating rate method and positron annihilation. Complementing the experimental findings, theoretical simulations were conducted to elucidate the underlying mechanisms responsible for the observed ML defects. Density functional theory calculations were employed to investigate the energy levels, charge transfer processes, and lattice distortions within the heterojunctions under mechanical stress. Theoretical predictions were compared and validated against the experimental results. The integration of experimental and theoretical approaches provides a comprehensive understanding of the ML behavior of Pr3+-doped NaNbO3/LiNbO3 heterojunctions. The insights gained from this research contribute to the development of novel ML materials and pave the way for their applications in next-generation sensing and energy conversion devices.

Synthesis and thermoluminescence characteristics of beta irradiated nanocrystalline calcium aluminate doped with lanthanum oxides

This study investigated the thermoluminescence (TL) characteristics of calcium, a nano-phosphor doped with a rare earth element (lanthanum, La). Six different concentrations of dopants were prepared by the sol-gel method. The XRD data displayed that the particle size was 52.48 nm. The surface morphology was examined by SEM analysis. The highest TL response of the nano-phosphor CaAl2O4 was found with a dopant of 0.1 % La, which has the most intense TL peak. The Computerized Glow Curve Deconvolution (CGCD) and Variable Heating Rate (VHR) methods were carried out for trap-level analyses and activation energy determination. The deconvolution of the glow curves displayed thirteen superimposed TL glow peaks located between 362 and 717 K. The TL response of CaAl2O4:0.1 % La nano-phosphor showed linearity in the beta dose range from 2.2 Gy up to 330 Gy for all the deconvoluted glow peaks. The minimum detectable dose of the prepared samples is 284 μGy. Other parameters, such as the sensitivity and reproducibility of the prepared samples, were determined. It is concluded that CaAl2O4 with a dopant of 0.1 % La is a good material for dosimetry applications.

Thermoluminescence dosimetric characteristics of natural zircon

The dosimetric characteristics were studied for natural zircon extracted from beach sand of grain size 106 micron to assess whether it can be used as a retrospective dosimeter. Zircon was extracted from the beach sand of Tirunelveli district, Tamilnadu. By analyzing the TL peaks between the room temperature and 450°C it was found to consist of two low temperature peaks (LTP) at 99 and 128°C and the high temperature broad peak (HTP) at 270°C when read at a heating rate of 5°C/sec. The initial rise method, Tm–Tstop, various heating rate method (VHR), Beta dose response and fading studies were carried out for the HTP. From the initial rise method the activation energy levels were found to vary from 0.8 to 1.6 eV. By the Tm–Tstop method it was found that the high temperature broad peak (HTP) at 270°C was a superposition of 6 TL peaks. The Im− Tm dependence curve was plotted and the value of the kinetic order was found to be 1.3. Beta irradiation between the dose levels 0.5 Gy to 100 Gy was used to study the linearity of dose response. It's observed that the zircon sample shows linear dose response up to 100 Gy of beta dose. Fading of the high temperature peak within 1 hour under bright sunlight was found to be ∼21% and after 24 hours the sample exhibited a fading of 47%. Repeatability test were also carried out for the HTP.

Unusual heating rates, dose responses and kinetic parameters detected on thermoluminescence from YAl3(BO3)4:Sm3+ phosphors

This study focused on the thermoluminescence (TL) characteristics of YAl3(BO3)4 (YAB) phosphors modified with various contents of Sm3+ ions. The TL response of the YAB: Sm3+ phosphors exposed to beta irradiation was measured across the temperature range of 25–500 °C, exhibiting three TL maxima at 70, 235, and 408 °C. Preheating protocol was also carried out to remove the low temperature TL peak followed by further experiments with the two-remaining high-temperature peaks. In the TL measurements conducted with variable heating rates (HR) between 0.1 and 5 °Cs-1, an anomalous heating rate behaviour was observed. A semi-localized transition model was used to address this feature. There was a standard deviation of less than 5% in the reusability measurements. The results of the kinetic parameters obtained by initial rise (IR) and various heating rate (VHR) methods were compared with those obtained by glow curve deconvolution (GCD) method. Tm-Tstop analysis revealed a continuous distribution of trap levels with a trap depth ranging from 1.35 to 2.20 eV. Through the use of GCD, the glow curve was found to demonstrate general order kinetics and consist of seven superimposed traps. The values of the kinetic parameters obtained for the glow curve agreed with those obtained by other methods excluding the VHR method encountering an anomalous impact. The results obtained from these tests showed that the sample could be successfully used for TL dosimetry applications.

Thermoluminescence and optically stimulated luminescence properties of NaMgF3:Dy,Eu synthesized by hydrothermal method and DFT calculations for the bandgap

This study indicates Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) radiation dosimetry characteristics for NaMgF3:Dy1%,Eu0.1% fluoroperovskite. Nanocrystalline NaMgF3:Dy1%,Eu0.1% material was synthesized by hydrothermal technique. The structure and optical properties were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), derivative thermogravimetry (DTG), radioluminescence (RL) and photoluminescence (PL) techniques. The bands on RL spectrum at 365, 488 and 477 nm might be attributed to Eu,2+ Eu3+ and Dy3+ ion emissions, respectively. The experimentally obtained TL glow curve was analyzed by the computerized glow curve deconvolution (CGCD) and various heating rate (VHR) methods and the order of kinetics (b), activation energy (E), and frequency factor (s) were determined for the appeared four peaks of the TL glow curve with 2°C /s heating rate. The energy bandgaps were calculated and the dependence of bandgap on composition was reported through the Density Functional Theory (DFT) computation.

Thermoluminescence properties of Cu doped α-Al2O3 crystals synthesized by a solid state method

While impurity doping in aluminum oxide (Al2O3) crystals has proven to be an efficient approach to enhance the material response to ionizing and nonionizing radiations, significantly less attention has been paid to thermoluminescence (TL) properties of copper doped Al2O3 (Al2O3:Cu) compounds. Here, Al2O3 microparticles (MPs) are synthesized and doped with different concentrations of Cu (0.1–1 mol%) using a solid state method. Scanning electron microscopy (SEM) was used to investigate the morphology and size of the synthesized MPs. The crystal structure and composition of the α-Al2O3 sample were studied by X-ray diffraction (XRD) and X-ray energy diffraction (EDX) analyses, respectively. The optimal amount of impurity for the maximum TL response to gamma rays of 60Co source was found to be 0.5 mol%. The kinetic parameters of the TL glow curve of the prepared samples were calculated by a computer fitting method. Also, the isothermal decay and variable heating rate methods were used to determine the activation energy and the frequency factor of the TL glow curve. Other TL properties of these MPs, including the TL glow curve, extinction and linear dose response region were also investigated.

Analysis on the thermal decomposition kinetics and storage period of biomass-based lycorine galanthamine.

As global ageing deepens and galanthamine is the preferred clinical drug for the treatment of mild to moderate Alzheimer's disease, it will be valuable to examine the behaviour and mechanism of galanthamine's thermal decomposition for its quality control, formulation process, evaluation of thermal stability, and expiry date in production. In order to study the pyrolysis of galanthamine hydrobromide with nitrogen as the carrier gas, a thermogravimetric-differential thermogravimetric technique (TG-DTG) was applied at a temperature rise rate of 10Kmin-1 and a volume flow rate of 35mLmin-1. The apparent activation energy E a and the prefactor A (E a = 224.45kJmol-1 and lnA = 47.40) of the thermal decomposition reaction of galanthamine hydrobromide were calculated according to the multiple heating rate method (Kissinger and Ozawa) and the single heating rate method (Coats-Redfern and Achar), and the most probable mechanism function was derived, and then the storage period was inferred from E a and E. A three-dimensional diffusion mechanism was suggested to control the thermal decomposition of galanthamine hydrobromide in accordance with the Jander equation, random nucleation and subsequent growth control, corresponding to the Mample one-way rule and the Avrami-Erofeev equation. As a result, the thermal decomposition temperature of galanthamine hydrobromide gradually increased with the rate of temperature rise. From Gaussian simulations and thermogravimetric data, galanthamine hydrobromide decomposed at the first stage (518.25-560.75K) to release H2O, at the second stage (563.25-650.75K) to generate CO, CO2, NH3 and other gases, and finally at the third stage (653.25-843.25K) to release CO2. After 843.25K, the residual molecular skeleton is cleaved to release CO2 and H2O. According to the E a and A presenting in the first stage of thermal decomposition, it is assumed that the storage life of galanthamine hydrobromide at room temperature 298.15K is 4-5years.

Anomalous dose behaviour of thermoluminescence glow curves and kinetic analysis of beta irradiated YAl3(BO3)4:Tb phosphor

With the aid of thermoluminescence (TL), we have extensively studied YAl3(BO3)4 host matrices incorporated with Tb3+ at different doping contents, which have been produced by combustion. The measured the TL glow curves exposed to beta rays at different doses consisted of four broad peaks located at around 76, 126, 230, and 378 °C. The peak maximum of the 230 °C TL peak shifts toward higher temperatures after 5 Gy beta irradiation while the other peak maxima almost remain constant. It is peculiar that 230 °C peak maximum shifts to higher temperatures with increased radiation dose and can be attributed to the multiple phases of the sample. A TL glow curve exhibits a proportional increase in intensity with increased the heating rate. A discussion of the possible causes of this pattern is provided. Observed peaks using the Tm─Tstop method are due to the presence of a quasi-continuous distribution of traps. The parameters of the traps have also been estimated using various heating rate methods in excellent agreement with one another.

Single heating rate methods are a faulty approach to pyrolysis kinetics

Single heating rate methods are a faulty approach to pyrolysis kinetics

Comparison of thermoluminescence characteristics of undoped and europium doped YAl3(BO3)4 phosphor synthesized by combustion method: Anomalous heating rate, dose response and kinetic analyses

In this study, undoped and YAl3(BO3)4 phosphors doped with Eu3+ at varying concentrations (x = 0.5 to 7 wt%) produced by a combustion process have been thoroughly examined by using the X-ray diffraction (XRD) and thermoluminescence (TL) techniques. The crystallized phosphors were confirmed by XRD analysis, and its crystal structure was examined. XRD analyses of the synthesized phosphor is in accordance with ICSD File No 96-152-6006. TL glow curve of undoped sample produced three glow peaks located at 80 °C, 240 °C, and 360 °C with a heating rate of 2°Cs−1 whilst Eu3+ doped one appears at 90 °C, 230 °C, and 390 °C. The undoped example complied with the theory as expected, namely, as the heating rate increased, the TL glow curve shifted towards lower temperatures and decreased in intensity. However, an anomalous change was observed in the sample with Eu3+ additive. The experimental findings from the dose-response of YAl3(BO3)4:0.5 wt%Eu3+ demonstrate that the intensity of TL provided by the total area under glow curves has an acceptable linearity (r2:0.999) up to 100 Gy. The intensity of each maximum on the TL glow curve augments proportionally as the heating rate is augmented. Possible reasons of this behaviour are discussed. Various heating rate (VHR) methods (such as Hoogenstraaten's and Booth-Bohun-Parfianovitch) have also been used to estimate kinetic parameters (e.g., energy and frequency factor), which seem to be in good agreement with each other.

Study on the Densification of Osmium by Experiment and First Principle Calculations.

The sintering of osmium is critical for the preparation of raw material targets for film coating, which is the main application area of osmium. In order to get a better understanding of the intrinsic mechanism of densification of osmium, a serial study on the sintering behavior of osmium has been made in this study. By the master sintering curve (MSC) and constant heating rate (CHR) method, the sintering activation energy of nanosized osmium is evaluated to be about 340 kJ/mol, which is higher than most other metals. The density-functional theory calculation indicates the higher energy barrier of the surface atom and vacancy migration and lacking migration tunnel of inner point vacancies. For example, the diffusion of osmium atoms on the surface of particles is mainly limited by Os (1010), which has an energy barrier as high as 1.14 eV, that is higher than the W atom on W (110) of 0.99 eV. The vacancy migration energy barrier inside osmium's grains is higher than 3.0 eV, while that of W is only 1.7 eV. This means that it is more difficult for osmium to achieve a high density compared with W, which is consistent with the experimental results. Accordingly, the proposed strategy provides a new opportunity to design a sintering process for target fabrication with excellent properties for various applications.

Novel green emitting Tb3+ doped KCaF3 phosphor for WLEDs and TLD applications

Multifunctional green emitting (Potassium Calcium Fluoride: x Trivalent Terbium) KCaF3: xTb3+ (x = 0.01, 0.03, 0.05, 0.07, 0.09, and 0.11 mol%) phosphor was synthesized by solid state reaction method. Crystal structure, morphology, photoluminescence and thermoluminescence properties were investigated in detail. Photoluminescence emission spectrum showed the characteristic maximum intensity peak at 543 nm corresponding to Tb3+ emission band when excited using an UV light of wavelength 374 nm. The concentration quenching effect of Tb3+ in KCaF3 phosphor was caused by dipole – quadrupole interaction between Tb3+ ions. CIE coordinates of KCaF3: xTb3+ (x = 0.05 mol%) was found to be x = 0.2959 and y = 0.6592 positioning at green region. Beta irradiated thermoluminescence glow curve was recorded on KCaF3: xTb3+ (x = 0.05 mol%) phosphor. Low temperature signals in TL glow curve were removed using bleaching or preheating technique. The optimization of preheat temperature was performed using different temperature and found 125 °C (peak 1) and 210 °C (peak 2) as an optimized temperature. Temperature of maximum TL intensity (Tm) of peak 1 and peak 2 was found to be 181 °C and 292 °C, respectively. The activation energy (Ea) and frequency factor (s) of peak 1 and peak 2 were calculated using peak shape method and variable heating rate method (VHR). Characteristic studies for dosimetry application such as dose response and reusability of KCaF3: xTb3+ (x = 0.05 mol%) were investigated in detail.

Iso-conversional analysis of thermally induced glass transition in some quaternary glasses of SeTeSnGe system

The study of glass transition and its consequences is an essential task to decide the utility of glasses (ChGs) at the industrial level. The model fitting non-isothermal methods provide information about the glass transition in terms of the related overall activation energy. However, thermal analysis of the activation energy at the different extent of conversions reveals the features of glass transition more deeply as compared to the non-isothermal model-fitting methods. Keeping in mind this fact, we have studied the iso-conversional glass transition in Se78-xTe20Sn2Gex (STSG ChGs, x = 0, 2, 4, and 6) glasses using calorimetric experiments in Differential Scanning Calorimetry (DSC).The temperature dependence of the extent of conversion (i.e., glass transition fraction αg) and the variation of activation energy Eg and rate constant with αg have been studied. Further, the various heating rate method has been chosen to study the correlation between the iso-conversional rate constant and corresponding activation energy. The variation of Eg with αg for the present samples of Se78-xTe20Sn2Gex indicates the occurrence of the rigidity transitions after x = 2 because of the abrupt growth in the number density of edge-sharing tetrahedral species of GeSe4 over the corner-sharing species.

Thermal properties and pyrolysis kinetics of phosphate-rock acid-insoluble residues

In the phosphorous–sulphur two-step process for the clean production of phosphoric acid, a phosphate-rock acid-insoluble residue (PAIR) is a solid filter residue obtained via the phosphoric acid acidolysis of phosphate rock (PR). PAIR combined with other raw materials can be used to prepare cement, ceramics and glasses, opening a potential avenue for large-scale PAIR utilisation. However, the preparation of such materials requires high-temperatures calcination. Understanding the high-temperature thermal properties of PAIR can enable its more targeted comprehensive utilisation or disposal. In this study, the thermal properties and pyrolysis kinetics of PAIR were systematically studied using a multiple heating rate method based on thermogravimetric analysis and a kinetic model. Results showed that from room temperature to 1200 °C, the main changes in the PAIR were the complete removal of fluorine and sulphur, partial removal of phosphorus and conversion of quartz to cristobalite. Moreover, during these processes, H2O(g), NH3, N2, CO2, SO2, P2O5(g), CO, CF3+ and organic gases were volatilised. Herein, the pyrolysis kinetics of PAIR is divided into five stages. Stage 1 (conversion rate ɑ: 0.05–0.2) conforms to the random nucleation and growth as well as the Avrami–Erofeev (n = 2/3) mechanism; the corresponding mechanism function is F(ɑ) = [−Ln(1 − ɑ)]2/3. Stage 2 (ɑ: 0.2–0.4) conforms to the first-order chemical reaction mechanism; the corresponding mechanism function is F(ɑ) = −Ln(1 − ɑ). Stage 3 (ɑ: 0.4–0.6) conforms to the phase boundary–controlled reaction and one-dimensional movement mechanism; the corresponding mechanism function is F(ɑ) = ɑ. Stage 4 (ɑ: 0.6–0.8) conforms to the three-dimensional diffusion process (Jander model); the corresponding mechanism function is F(ɑ) = [1 − (1 − ɑ)1/3]2. Stage 5 (ɑ: 0.6–0.95) conforms to the one-dimensional diffusion process; the corresponding mechanism function is F(ɑ) = ɑ2.

Radioluminescence results, thermoluminescence analysis and kinetic parameters of Y2O3:Ln3+ (Ln: Dy, Nd, Sm) nanophosphors obtained by sol-gel method

Dy3+, Nd3+, Sm3+ doped Y2O3 nanophosphors were produced with high homogeneity at low sintering temperature using the sol-gel method. To compare the structural and optical changes of different rare-earth ions included in the crystal lattice, the dopant ratio was chosen as constant 2 mol%. In the light of X-ray diffraction (XRD) analysis, the unit cell volume and average crystallite size of the doped nanophosphors and their pure Y2O3 sintered under the same heat treatment regime were calculated and compared. Scanning electron microscopy (SEM) techniques were used to describe their structures and morphologies; an average particle size histogram of nanostructures was generated. The Radioluminescence (RL) spectra of Y2O3:Ln3+ (Ln: Dy, Nd, Sm) nanophosphors were presented for the first time. Splittings were seen in detail in the emission spectra given the 200–1100 nm range. For Dy3+4F9/2 → 6H13/2, for Nd3+; in the visible region 4H11/2-4I9/2 in the NIR region 4F3/2-4I9/2, for Sm3+; in the visible region 4G5/2-6H7/2 in the NIR region 4G5/2-6F5/2 transitions were determined to have the most vigorous emission. It was observed that the optical band gap calculated from the absorption spectrum of Y2O3 was 4.97 eV; this value changed the most with Dy contribution and decreased to 4.77 eV. The thermoluminescence (TL) behaviors of nanophosphors were compared under both UV and X-ray excitation. The kinetic parameters were calculated by applying computerized glow curve deconvolution (CGDC), and various heating rate (VHR) methods to the glow curves obtained UV excitation. The obtained E (eV) values correlated with each other are highly compatible.

Errors in the Activation Energy and Thermal Quenching Parameters When Evaluated from Quenched Thermoluminescence Glow Peaks Using the Various Heating Rates Method

It is generally observed that the various heating rates (VHR) method overestimates the activation energy (E) when applied to quenched thermoluminescence (TL) peaks. Based on the analysis of numerically computed quenched TL peaks, we introduced an empirical expression that estimates the error in E. The expression correlates the error in E with the width of the peak, the luminescence efficiency and its first derivative at the lowest heating rate evaluated at the temperature of peak maximum. In addition, the expression accurately predicts the temperature shift of the peak maximum as a function of the heating rate. The VHR-based methods used to evaluate the quenching parameters (W and C) result in erroneous values. The source of error in the peak area-based method is the replacement of the unquenched peak area by the quenched peak area at the lowest heating rate as usually practiced in the literature. Accurate values of W and C were obtained when we modified the basic equation to include the luminescence efficiency at the lowest heating rate. On the other hand, we explicitly showed that the maximum intensity-based method used to evaluate these parameters is not suitable due to the lack of a reference point.