Thermoluminescence Curves Research Articles

Trap level spectroscopy of disordered materials using thermoluminescence: An application to aluminosilicate glass

A method is presented for analyzing complex thermoluminescence (TL) glow curves from disordered materials using aluminosilicate glass as an example. The method is first described using simulated TL glow curves, firstly by assuming a Gaussian distribution of trap depths Et and a fixed frequency factor s, and secondly by assuming distributions of both Et and s. The method is able to reproduce the input distributions for both Et and s with a high degree of accuracy. The method is then applied to the measured TL from an aluminosilicate glass sample. A series of glow curves is recorded at different heating rates and the method is first applied to each glow curve separately, and Et and s distributions are obtained; four different trapping sites are revealed within the material, each with distributions in Et and s. Good self-consistency is obtained at each of the different heating rates. The lowest temperature TL peak shows signs of fading at the lowest heating rates used. The method is then applied to a “pseudo” TL curve consisting of the sum of all individual glow curves obtained at the different heating rates as a simple way to fit all curves recorded at the different heating rates simultaneously. The results obtained are consistent with those obtained by fitting the glow curves individually.

Estimate half-life of thermoluminescence signals according to the different models by using Python

In this study, the half-life is the time required for the thermoluminescence intensity to drop to half of its initial value. The half-life is a characteristic of the optical and thermal properties of the material. The half-life of the thermoluminescence signals under other models such as first order kinetics, second order kinetics, general order kinetics, mixed order kinetics and the one-trap one-recombination was calculated. The specific goals of this work are to give the half-life difference of the thermoluminescence signal of each model by using Python. The formulas allow to quickly determine the half-life of the simulated or empirical thermoluminescence curve, including one or more complex peak. Simulation results and calculations based on the figure of merit parameters allow to check the calculation of the half-life according to the most suitable model.

On the application of the various heating rate method to determine the activation energy of the dominant trap from a complex TL peak

The various heating rate (VHR) method is used to determine the activation energy (E) of traps responsible for thermoluminescence (TL) peaks. The VHR method was developed and works well for single glow peaks. However, it is often applied to multiple overlapping peaks where one of the peaks is dominant. The use of VHR method for TL curves consisting of several peaks for determining the activation energy of the dominant peak may, due to an arbitrary selection of the heating rate set adopted for calculations, lead to a different result than the actual physical value of this parameter. The purpose of this work is to show how different results can be obtained using various heating rate sets in the VHR method for curves composed of two peaks with one clearly dominant. The method was used for several examples of TL curves generated numerically in such a way that the impact of the ratio of peak intensities, or peak mutual position on determining the energy may be observed.

Study of Photoluminescence,Thermoluminescence, and Afterglow properties of Dy3+ doped Ba2ZnSi2O7 phosphor

Barium Zinc Silicate Ba2ZnSi2O7 (BZS) phosphor doped with Dysprosium (Dy3+) was prepared at 1200 °C in the air by a solid-state reaction method. The prepared phosphor shows an efficient blue and yellow emission centered around 480 nm and 580 nm, respectively under UV excitation, which is believed due to incorporation of Dy3+ ion. The optimum concentration for Dy3+ ion is at 2 mol% and concentration quenching is attributed to exchange interaction. The CIE diagram is drawn for the whole series of phosphor samples prepared and it confirms that emission color had, indeed, tuned with the incorporation of Dy3+ ion in the BZS samples. The afterglow properties and Thermoluminescence (TL) have also been studied. TL curve confirms the presence of at least four traps in the phosphor material. The present results suggest BZS:Dy3+phosphor is a promising one for display and dosimetry application.

Sensitizing effect of Nd3+ on Tb3+ activated ZrP2O7 long persistent phosphor materials

The long persistent phosphors of Zr0.97P2O7:0.018Tb3+,0.012Nd3+ with Nd3+ as sensitized ions and Tb3+ as emission centers were synthesized using high temperature solid state reaction. The crystal structure and defects, excitation and emission spectra, decay curves and thermoluminescence (TL) curves of the phosphors were investigated. The synthesized Zr0.97P2O7:0.018Tb3+,0.012Nd3+ is essentially in line with the standard card PDF#49-1079. The emission band with main peak at 548 nm exhibits the characteristic transitions of 5D3-7Fj (j = 5, 4) and 5D3-7Fj (j = 6, 5, 4, 3) of Tb3+. The analysis of excitation and emission spectra shows that there exists the overlap between the emission peaks of Nd3+ at 466 and 485 nm and the excitation of Tb3+ at 443 and 485 nm, and the energy transfer from Nd3+ to Tb3+ plays an important role in the improvement of luminescence properties. The decay curves shows that Zr0.97P2O7:0.018Tb3+,0.012Nd3+ has longer afterglow time than ZrP2O7 and Zr0.982P2O7:0.018Tb3+. Additionally, the TL curves indicate that the trap depth at 0.72 eV in Zr0.97P2O7:0.018Tb3+,0.012Nd3+ is to the benefit of the afterglow time. The possible luminescence mechanism of ZrP2O7:Tb3+,Nd3+ is proposed on the basis of the XPS spectra, EPR spectra, excitation and emission spectra, decay curves, TL curves and the analysis of defect equations.

Investigation of structural and thermal response of Sm3+ doped Sr3MgSi2O8 phosphors

Present study deals with the effect of Sm3+ doping on crystal and optical behaviour of Sr3MgSi2O8. For these studies prepared phosphor was characterized by using X-ray powder diffraction and luminescence spectra by recording excitation and emissions spectra. Emission spectra have emission wave lengths centered at 490 nm and 545 nm. Effect of Sm3+ ion concentration shows dipole–dipole interaction was responsible for the quenching shown by phosphor. The thermoluminescence curves were used to define the ability of the trap to trapping the carriers for Sm3+ doped Sr3MgSi2O8 phosphor.

Spectrally Resolved Thermoluminescence of Anion‐Deficient Al2O3–BeO Ceramics for High‐Dose Dosimetry

Thermoluminescence (TL) curves of Al2O3–BeO ceramic samples synthesized during high‐temperature treatment of nanostructured Al2O3 compacts in vacuum with the presence of graphite in BeO crucibles are studied. Temperature ranges of certain TL peaks emission at the synthesis temperature varied from 1200 to 1400 °C are found. A comparative analysis of the TL peaks temperature position and the nature of traps in the obtained ceramics with single crystalline Al2O3, BeO, and BeAl2O4 analogs is carried out. Spectral composition of different TL peaks is investigated. It is found that oxygen vacancies and their aggregates play the main role in the TL emission centers formation in the samples under study. A complex structure of the dominating luminescence band at 4.0 eV in the dosimetric peak at 530 K of the ceramics synthesized at 1400 °C is found. This band is shown to be a superposition of three bands with the maxima at 3.11, 3.80, and 4.17 eV, resulted from F, F+ centers and presumably from Fcat‐type centers in aluminum oxide. The obtained results are essential to control and modify TL properties of Al2O3–BeO ceramics to create luminescence detectors of high‐dose radiation.

Novel white-emitting afterglow phosphor Na2CaSn2Ge3O12:Dy3+: Preparation, photoluminescence, and phosphorescence properties

Afterglow was found in germanate (Na2CaSn2Ge3O12) doped with Dy3+ phosphor, which was prepared at 1250 °C through the traditional solid-state reaction in air. Na2CaSn2Ge3O12:Dy3+ phosphors were comprehensively characterized by XRD, photoluminescence excitation and emission spectra, thermo-luminescence and long persistent phosphorescence decay curves to study the effects of the Dy3+ concentration on their properties. The XRD results indicates that a single phase of Na2CaSn2Ge3O12 can be obtained. Upon excitation by 248-nm UV light, all samples emit white light, which is composed of yellow and blue originating from the Dy3+ (4F9/2→6HH/2, H = 11, 13, 15 transition). The Na2CaSn2Ge3O12:Dy3+ phosphor exhibited the perfect luminescent property and longest afterglow time when the Dy3+ concentration was 0.6 mol%. The CIE chromaticity coordinates for Na2CaSn2Ge3O12:Dy3+ were (0.3916, 0.3914). From the long persistent phosphorescence decay curve of the Na2CaSn2Ge3O12:Dy3+ phosphor, it was concluded that this process contains a fast and a slow decay. The afterglow luminescence from the Na2CaSn2Ge3O12:Dy3+ phosphor persisted for more than 7.8 h after irradiation with ultraviolet lamp. The Na2CaSn2Ge3O12:Dy3+ phosphor is deemed to be a potential storage phosphor that can be applied in the field of practical application. After incorporation of Dy3+ into the Na2CaSn2Ge3O12 matrix, new foreign traps (DyCa°, DyNa°°) were produced, and the concentration of internal traps (VCa″, VNa′) increased approximately 10 times. The luminous mechanism of the Na2CaSn2Ge3O12:Dy3+ phosphor was studied.

Optical and x–ray scintillation properties of X2MnCl4 (X = PEA, PPA) perovskite crystals

An emerging prospect of solution-processed organic–inorganic hybrid halide perovskites is promising for next generation x-ray imaging applications. Herein, the optical and x-ray scintillation properties of lead-free two-dimensional perovskite crystals are reported, i.e. X2MnCl4 (X = PEA, PPA). At room temperature (RT), the photoluminescence (PL) spectra of both crystals show a peak around 600 nm with the lifetime between 3 and 4 µs, making them applicable for scintillator in x-ray imaging applications. Materials with a small electronic band gap of about 2 eV may allow a good promise for high-light-yield scintillators. On the other hand, x-ray luminescence (XL) measurements for both crystals show no spectra at RT, while those at 10 K exhibit the similar features observed in PL spectra. Temperature-dependent XL intensities reveal thermal quenching behaviour with activation energies between 40 and 54 meV. Thermoluminescence (TL) and glow curves in both crystals show residual luminescence background as slow as 1648 s and some deep traps with energies as large as 190 meV. Thermal quenching and TL measurements of both crystals are the opposite of those of PEA2PbCl4 crystals. Although some properties may not be beneficial for scintillators, the small differences of scintillation properties in both crystals may provide direction for the new designs of high-light-yield lead-free perovskite single crystal scintillators.

Thermoluminescence characteristics of Bi12SiO20 single crystals

Trapping center properties of bismuth silicon oxide (Bi12SiO20) single crystals were investigated by thermoluminescence (TL) measurements performed in the 50–400 °C temperature range. Experimental TL curve recorded at heating rate of 1 °C/s presented two overlapped peaks around 279 and 362 °C. The heating rate dependency of TL curve was also studied for heating rates between 1 and 6 °C/s. The measured TL curves were analyzed using curve fitting, initial rise and different heating rate methods. The results of analyses indicated that TL glow curve is composed by two peaks associated with two discrete trapping centers at 0.81 and 1.10 eV. The revealed trapping centers were associated with intrinsic defects in the Bi12SiO20 compound under the light of previously reported papers. An energy band diagram was also plotted to indicate possible transitions within the forbidden band gap.

Luminescence of impurity and intrinsic defects of Na-doped alumina ceramic

Ceramics from alumina nanopowder doped with a different Na concentration were synthesized at high-temperature sintering under vacuum and in air at a varying temperature. Pulsed cathodoluminescence spectra and thermoluminescence curves were measured to study effects based either on the formation of new defects or on the modification of alumina intrinsic defects. In fact, the emission bands with maxima of 400, 510 and 693 nm are recorded on pulsed cathodoluminescence spectra of Al2O3:Na ceramics, which are respectively responsible for their intrinsic centers of alumina (F-centers), Na and Cr impurity centers. A decrease in the synthesis temperature results in an increase in the intensity of the 510 nm band. Sodium impurity concentration growth in ceramics results in the intensity growth of the given band. It is also shown that an increase in the sintering temperature causes an increase in the intensity of all thermoluminescence peaks. Thermoluminescence curves are also changed under β-irradiation.

UV–Vis-NIR broadband-photostimulated luminescence of LiTaO3:Bi3+ long-persistent phosphor and the optical storage properties

Abstract Trap depth is an important factor in the design of long-persistent (LPL) or photostimulated luminescence (PSL) materials, lithium tantalate is a promising matrix with abundant defect traps owing to the volatile lithium. The new long-persistent luminescence material LiTaO3:Bi3+ exhibits intense indigo blue photoluminescence (PL) and long-persistent luminescence with the maximum peak located at 430 nm, which is ascribed to the 3P1 → 1S0 transition of Bi3+, while the decay rate of afterglow increases when the concentration of Bi3+ dopant improves. Under near-infrared (NIR) stimulation, the synthetic phosphor shows bright indigo blue photostimulated luminescence, but the UV–Vis stimulation light can quench afterglow rapidly due to its efficient photostimulation effect related to the distribution and depth of defect traps in matrix crystal. By means of photostimulated luminescence spectra, thermoluminescence (TL) curves and X-ray photoelectron spectroscopy (XPS), the impact of antisite-tantalum defect traps on luminescence property is characterized. The findings give insight into the mechanism of photostimulated luminescence and expand the application field of long-persistent luminescence materials in optical information storage.

Long-persistent phosphorescence in Eu2+-doped calcium borate chloride for optical data storage

Yellow-emitting optical data storage phenomena were observed in a series of Ca2BO3Cl: Eu2+, Ln3+ (Ln = La, Ce, Pr, Sm, Gd, Tb, Ho, Tm, Yb, Lu) long-persistent phosphors. Eu2+ in Ca2BO3Cl could emit yellow light located at 580 nm ascribed to the 5d-4f transitions when optical data was being read out. As co-activators, Ln3+ had various effects in causing afterglow and changing trap concentration. Optical data storage phenomena occurred for each combination of Eu2+ and Ln3+ in calcium borate chloride host. Thereinto, prepared Ca2BO3Cl: Eu2+, Ce3+ phosphor presented a decent afterglow and optical storage property. Its afterglow decay time was more than 1 h at room temperature and had a bright yellow optical signal at 473 K Ca2BO3Cl: Eu2+, Ho3+ showed an optimum optical storage property, which remained bright yellow light even after 7 days of data storage. This outstanding optical data storage performance was mainly derived from Ho3+ increased the trap concentration of oxygen vacancies. The crystal structure, excitation and emission spectra, afterglow decay curves and thermoluminescence curves were measured and analyzed in all Eu2+ and Ln3+ doped Ca2BO3Cl samples. A simple optical data storage method was set up and effective optical signals were observed. Based on these results, detailed optical data storage processes and possible mechanism were studied and discussed.

Experimental and modeling study of charge carriers release from traps by interaction with molecular vibrations in silicon organic polymers

The dependence of the charge carrier’s release from traps on the polymer ordering and the widths of the vibration bands are investigated in five silicon organic polymers using thermoluminescence in the 5–200 K temperature range and the Raman spectra. The influence of the vibrations on the thermoluminescence is caused by the processes of the charge carriers’ release from traps via the absorption of vibration quanta. The effect manifests itself in both the appearance of discrete levels of the carriers’ activation energy which coincides with the energy of the vibration quanta and the formation of a structure on the thermoluminescence curve. It is shown, that the magnitude of effects depends on the widths of optical vibration bands and the ordering of the polymers. The mechanisms of interactions of trapped charges with molecular vibrations are analyzed and the values of microscopical parameters of such interactions are determined. It is shown that the contribution of molecular vibrations in the charge release from the trap is great.

Discovery of near-infrared persistent phosphorescence and Stokes luminescence in Cr3+ and Nd3+ doped GdY2Al3Ga2O12 dual mode phosphors

The near-infrared (NIR) luminescence materials have attracted great attention on account of their potential applications in optical imaging field. In this paper, a series of Cr3+ and Nd3+ doped GdY2Al3Ga2O12 phosphors with luminescence in the biological windows were synthesized using a solid-state reaction method. The crystal field parameters, concentration dependent photoluminescence and persistent luminescence properties of Cr3+ were discussed in detail. Nd3+ ions exhibit perfect NIR to NIR Stokes luminescence in the host. The influence of Nd3+ doping concentration was studied by emission spectra and decay curves. Taking the advantages of both Cr3+ and Nd3+, dual mode phosphors with NIR persistent luminescence and NIR to NIR Stokes luminescence were designed and achieved. Based on the energy transfer process, persistent luminescence and thermo-luminescence curves, the luminescence mechanism was proposed.

The trap control in the long afterglow luminescent material (Ca,Sr)2MgSi2O7:Eu2+,Dy3+

A series of long afterglow luminescent materials (Ca,Sr)2MgSi2O7:Eu2+,Dy3+ doped with R+ (R+ ​= ​Li+, Ag+, K+ respectively) was synthesized by the high temperature solid-state reaction method. Crystal structure and luminescent properties were analyzed by X-ray diffraction (XRD), photoluminescence (PL), decay curves and thermoluminescence (TL) curves. The results show that the addition of ions has no effect on the crystal structure type and the position of the emission peak. However, the incorporation of doping ions has a great impact on the crystal field environment of the luminescent center. The introduction of R+ ions increases the number of shallow traps, reduces the number of deep traps, improves the initial brightness and the brightness decrease during slow decay. At higher Dy3+ doping level, more deep traps are introduced to these materials, and it effectively improve the brightness of the slow decay process. The mechanism of afterglow in the (Ca,Sr)2MgSi2O7:Eu2+,Dy3+,R+ materials is discussed.

Determination of thermoluminescence parameters in nanocrystalline CaAl2O4

This paper is a critical investigation of trap levels present in nanocrystalline CaAl2O4. The technique of thermoluminescence (TL) is used to determine the trap levels. Unlike most workers, we use Computerized Glow Curve Deconvolution (CGCD) technique to decode the TL curves that enables us to determine all the three key trapping parameters, namely, the activation energy (E), the frequency factor (s) and the order of kinetics (b). Using these as inputs we evaluate the electron lifetime (τ) of charge trapped in different traps. This provides the vital information of the possible use of CaAl2O4 based phosphors for practical application in dosimetry, scintillation and persistent luminescence.The phosphor contains multiple discrete trap levels in the band gap (Eg = 7.4 eV) with trap-depths 0.69 ± 0.02, 0.83 ± 0.01, 0.99 ± 0.02, 1.06 ± 0.02, 1.18 ± 0.03, 1.28 ± 0.02 and 1.41 ± 0.01 eV. The magnitudes of the frequency factors (s) for all the cases are ≈109 that translates the Urbach's coefficient as 23.47 ± 0.14. We believe this work is first of its kind in providing complete parameters of trap levels in CaAl2O4 phosphor. The life times at Room temperature (τ300) of the change in these varies are spread are a wide range of 18 min ≤ τ300 ≤ 1007 years which show that CaAl2O4 based phosphors can be designed for specific application with appropriate trap level modification. This explains the excellent persistence luminescence in CaAl2O4: Eu2+, Nd3+ that will be discussed in detail.

Luminescence behavior of Nd3+/Zr4+/3+ Co-activated ZrP2O7 persistent phosphor

The bluish-green long persistent phosphor (LPP) materials ZrP2O7:Nd3+ were synthesized in a reducing atmosphere by a conventional high-temperature solid state reaction. The XRD patterns, XPS survey scan, excitation and emission spectra, decay curves and thermoluminescence (TL) curves were used for investigating the structure and luminescence properties and mechanism of the materials. The emission band between 400 and 600 nm exhibit the characteristics of blue emission from d-d transitions of Zr and the characteristics of green emission from f-f transitions of Nd3+. The TL curves showed that the formation of high-concentration trap level at 337 K (0.73 eV) was mainly responsible for the LPP phenomenon of ZrP2O7:Nd3+ at room temperature.

High efficient Eu3+-activated Ca(La, Gd)MgSbO6 double perovskite phosphors: Thermal stability improvement by composition modulating

A series of high efficient Eu3+-activated Ca(La, Gd)MgSbO6 phosphors were synthesized. Based on CaLaMgSbO6:Eu3+, Gd3+ was used to replace La3+ to improve the luminescence properties. Structure information was obtained by X-ray diffraction and the software Diamond. Site occupancy, coordinates and the lattice parameters were obtained by Rietveld refinement. Site occupancy of La3+/Gd3+ was rather close to the stoichiometric proportion. The photoluminescence (PL) intensity was enhanced under ultraviolet (UV) light. Schematic illustration of energy transfer and energy level were performed to show the luminescence process. UV–visible diffuse reflectance spectra were carried out to obtain the band gap. This phosphor presented great thermoluminescence (TL) stability based on the TL curves. Quenching mechanism was investigated in detail by means of the band gap. The luminescence properties manifest that this kind of double perovskite phosphor is a good candidate for solid-state lighting.

Proton Beam Induced Modification of Luminescence Properties of Polystyrene/Al2O3 Polymer Nanocomposites.

Polystyrene polymer (PS)/Al2O3 nanocomposite films were synthesized from PS:Al2O3 (1-x):x mixtures (x = 3wt%) via solution casting method. These nanocomposite films were exposed to 5MeV proton beam of different fluences. The proton beam induced changes in optical and luminescence properties of PS and PS:Al2O3 films have been investigated using FTIR, UV-visible, Photoluminescence and thermoluminescence studies. FTIR studies concede reduction in the peak intensity due to doping of Al2O3 and proton irradiation. The UV-visible spectra show shifting of absorption edge with increasing fluence. This can be attributed to creation of conjugated system of bonds. The band gap of PS and 3wt% Al2O3 doped PS is observed to be 4.38eV and 4.34eV, respectively, whereas the band gaps of proton irradiated 3wt% Al2O3 doped PS films are found to be 4.28eV and 4.23eV at the fluences of 1 × 1012 ions/cm2 and 1 × 1013 ions/cm2, respectively. The photoluminescence emission spectra show three peaks, wavelength at 411nm, 435nm and 462nm corresponding to the PS in violet-blue region when excited with near UV wavelength of 380nm. The intensity of emission peaks was found to increase with increasing fluence. The thermoluminescence curves of PS/Al2O3 were analysed using glow curve deconvolution method (GCD). The increase in TL peak intensity of the glow curve was observed as fluence increase.