Enhanced Thermos luminescence Properties of Synthesized Monoclinic Crystal Structure

Sharma S and Dubey SK

Published on: 2023-03-25


Ba (NO3)2, Mg (NO3)2, SiO2 * H2O, NH2CONH2, Eu (NO3)3 and H3BO3 are used as the raw materials for the synthetization of Ba2MgSi2O7 (RE: Eu) nano sized powder sample using combustion synthesis technique (CST). X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and thermoluminescence (TL) spectra are employed to examine the effect of varying doping concentration of Eu ions on crystalline structure, surface morphology, and thermal characteristics. The monoclinic Ba2MgSi2O7 compound has a dominant phase characteristic, according to powder XRD patterns, and there are additionally dopants exist that have no discernible impact on the host crystal structure. This melilite group structure yields a layered compound. Standard JCPDS PDF file #23-0842 closely matched the synthesized powder sample's usual XRD patterns. The average particle size (D) of the flake- like Ba2-xEuxMgSi2O7 (x=0.05) phosphor is calculated to be nearly ~70 nm. Systematically examined and described are the thermal characteristics as expressed by TL glow curves. The observations demonstrate that a variety of UV exposure to radiation times, such as 5 minutes, 10 minutes, 15 minutes, 20 minutes, and 25 minutes, had almost no impact on the peak positions in the present spectra. Using TL glow curves and Chen's glow curve approach, the various trapping parameters, including trap depth or activation energy (E), frequency factor (s- 1), and shape factor (µg), are evaluated.


Phosphors, thermal properties, Ba2MgSi2O7, thermoluminescence, XRD, FESEM


Alkaline earth silicates or melilite-type phosphors have categorized structural formula X2T1T2 O, with a large cation site (where X=lanthanides ions or Na, Ca, Ba, Sr, Pb), while (T1 =Al, Si, Mg, Zn) and (T2 =Si, Al, B, Ge) are frequently linked by oxygen ions. It has established itself as the key example of long-lasting mechanism application [1]. Eu2+ doped alkaline earth magnesium disilicates (M2MgSi2O7:Eu2+; where M = Ca, Sr, Ba) have been widely investigated to produce efficient persistent luminescence as a consequence of the position of the 4f and 5d levels of the dopant Eu2+ ions in the host electronicstructures; seem to be of importance because they have the potential to confirm the efficacy of the rare earth ions to trap electrons/holes. [2]. Ba2MgSi2O7:Eu2+ (a monoclinic compound) is particularly significant due to its thermoluminescence characteristics under UV stimulation. As alkaline earth silicates [AESs] have quite a robust crystal structure and exceptionally high levels of stability in both chemical and physical terms, they have been extensively used for the luminous hosts. Ba2MgSi2O7 phosphor is an excellent host material because it decreases the probability that perhaps the killer centre will capture excitation energy [3]. Ba2MgSi2O7 seems to have a 1D (one dimensional) layer structure in addition to consisting of a monoclinic crystal structure. As a consequence, the eight oxide ions of SiO4 and MgO4 units are associated with the Ba2+ lattice site [4]. In a monoclinic configuration with the space group C2/c (No. 15), the host material crystallizes [5]. A further way to define the phenomenon of TL is as one of the most crucial approaches for performing a thorough evaluation of the trap-centers and trap-level in an insulator or semiconductor stimulated according to any radiation source [6]. Radiation dosimetry appears to be where TL phosphors are most frequently applied. When a mechanism is established, novel luminous materials can be used in many different ways. Radiation safety, health physics, and personal monitoring are all affected by TL dosimetry. Materials offer exceptional chemical and mechanical properties, high levels of sensitivity, little fading, and a low thresholddosage. They also have a low dependence on radiation energy [1, 7].

Although it probably suffers from non-uniform mixing and agglomerated particles that have an exceedingly wide range of particle sizes, M2MgSi2O7 (M= Ca, Ba, Sr) phosphors are mainly formed by traditional high-temperature solid-state reaction approach. The brightness and resolutions are severely restricted by aggregated and irregular particles during application. Due to the uniform particle formation and incredibly small size distribution, solution -based processes such as the sol-gel process, hydrothermal process, combustion synthesis process, and co-precipitation method, etc. The Ba2-xEuxMgSi2O7 (x=0.05) phosphor with controlled particles and superior luminescence properties have been synthesized by combustion synthesis techniques. It has been demonstrated beyond a dispute that the materials' crystalline morphology, size, and shape play a significant role in enhancing their capabilities. As a consequence, the comprehensive evaluation of the structural, morphological, and thermoluminescence features of the synthesized Ba2-xEuxMgSi2O7 (x=0.05) phosphor is reported in the present investigation.

Experimental Details

Powder Sample Preparation

Powder samples should be created using stoichiometric amounts of Barium nitrate [Ba (NO3)2], magnesium nitrate [Mg (NO3)2] and urea [CO (NH2)2] (All AR grade, 99.99% pure) weighed using Shimadzu ATX 224 single pan analytical balance are used as raw materials. In addition to it, europium nitrate [Eu (NO3)3] taken as co-activator. The small amount of boric acid (H3BO3) is used as the flux while the urea [CO (NH2)2] is used as fuel and all metal nitrates is used as an oxidizer. All precursor chemicals mixed homogeneously with adding a few drops of acetone (CH3COCH3), and grind in an agate-mortar & pestle [8]. After the solution is transferred into the alumina crucible with comparatively larger volume (30ml), it is placed into a furnace already maintained at a temperature of 6500C. Within 5 minutes, the furnace reaches the desired temperature and reaction starts giving whitish flame. This continues for next few seconds and as it is over, crucible is taken out of the furnace and kept in open to allow cooling. The mixture froths and swells forming foam, which ruptures with a white flame. Upon cooling, we get fluffy form of material, which is then crushed using agate pestle mortar (diameter -5") to get material in the powder form. Thereafter, the obtained powder samples were transferred in crucible and post annealed at 1000°C for 1 hour under a weak reducing atmosphere, which was produced with the help of burning charcoal. The resulting phosphor was formed as a white powder. The resultant powder sample was then placed back together in that manner and stored in an airtight, watertight bottle for the further structural, morphological, and thermal characterization studies. Figure 1 demonstrates the approach to making a powder sample quite clearly.

The entire process's chemical response can be summarized as follows:

Ba (NO3)2 + Mg (NO3)2 + SiO2*H2 O + NH2CONH2 + H3BO3Ba2MgSi2O7 + Gaseous Products [H2O (↑) + CO2 (↑) + N2 (↑)] + Energy  (1)

Ba (NO3)2 + Mg (NO3)2 + SiO2*H2O + Eu (NO3)3 + NH2CONH2+ H3BO3 → Ba2MgSi2O7: (RE: Eu2+) + Gaseous Products [H2O (↑) + CO2 (↑) + N2 (↑)] + Energy  (2)

Figure 1: Diagrammatic representation of synthesis of Ba2-xEuxMgSi2O7(x=0.05) phosphor via combustion synthesis technique.

Powder Sample Characterization Instruments

The materials are weighed using Shimadzu ATX 224 single pan analytical balance and the samples are prepared in a digital muffle furnace already maintained a temperature of 650oC. The material was characterized by powder X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Thermoluminescence (TL). To confirm the crystal structure, phase formation and powder photographs of the synthesized phosphors were examined using an X-ray diffractometer (D8 ADVANCED BRUKER) operating at 40 kV and30 mA with Cu-Kα radiation (λ= 1.54056 Å). The xrd data were recorded in 2θ range of 10° to 80°. The average crystallite sizes were calculated by Debye- Scherer empirical formula. Thesurface morphological porosity of the powder samples was obtained using field emission scanning electron microscopy using a ZEISS EVO Series EVO 18 scanning electron microscope. Thermoluminescence (TL) study was carried out for recording TL glow curve ofsynthesized phosphor; a routine TL setup (Nucleonix TL 10091) was used. The kinetic parameters were calculated by using Chen’s glow curve method. The samples were irradiatedwith UV-ray source. The heating is performed from room temperature (RT) and heating rate under thermal stimulation is varied 5oC/s.

Results And Discussion

XRD Analysis

The powder XRD patterns of the selected Ba2-xEuxMgSi2O7 (x=0.05) sample are displayed in Figure 2, and are compared with the standard pattern (JCPDS 23-0842) [9] of the host crystal lattice (Ba2MgSi2O7). The synthesised powder sample is revealed to consist of a single-phase monoclinic structure with a C2/c space group and to have no noticeable effect from the dopantEu2+ on the crystal structure of its host lattice. The radius of Eu2+ 0.117 nm is very close to thatof Ba2+ about 0.134 nm rather than Mg2+ 0.072 nm and Si4+ 0.041 nm [10]. As a result, it is predicted that the host Ba2MgSi2O7 will incorporate the Ba2+ lattice positions from the dopantEu2+ ions. The layered compound is formed by this melilite group crystal structure. Table 1 summarizes the typical crystal structure, phase structure, cell volume, and lattice parameters.

Table 1: Lattice Parameters of Synthesized Ba2-xEuxMgSi2O7 (x=0.05) Sample [11].

Lattice Parameters


Crystal Structure


Phase Structure

Akermanite [M2T1T2 O7]


Crystallography Group Member


Space Group



Lattice Constants

a = 8.4128 Å, b = 10.7101 Å,

c = 8.4387 Å, and


α = γ = 90°, β = 110.71°

Average Crystallite Size D (in nm)


Prominent Peak (2θ)


Cell Volume (V)

711 (Å)3



Eu2+ions are expected to replace Ba2+sites because the coordination number of Ba2+ion iseight and that for Mg2+ions and Si4+ions is four. It’s hard for Eu2+ions to incorporate thetetrahedral [MgO4] or [SiO4] symmetry but it can easily incorporate octahedral [BaO8] sites [12].

Figure 2: The XRD patterns of the samples Ba2-xEuxMgSi2O7 (x = 0.05) at room temperature along with the standard pattern (JCPDS 23-0842) of BMS for comparison.

Estimation of Crystallite Size

In comparison to the reference data, there seems to be a little shift in the XRD data towards thelarger angle. The average crystallite size (D) was derived from the XRD pattern through usingDebye- Scherrer equation [13], ???? = ????????/???????????????????? (3), where k (0.94) is the Debye-Scherrer constant, D is the crystallite size for the (hkl) plane, ???? is the wavelength of the incident X-ray radiation [Cu-Kα (λ= 0.154056 nm)], β is the full width at half maximum (FWHM) in radiations, and ???? is the corresponding angle of Bragg diffraction. The sharper and isolated diffractionpeaks such as 2???? = 22.42 (002), 27.51 (022), 29.22 (131), 31.16 (222), 32.69 (113), 54.14 (153) were chosen for calculation of the BMSE crystallite size. Based on the Debye- Scherrer's formula [14], the crystallite size is ~74nm, 76nm, 69nm, 68nm, 66nm, 67nm was calculated, respectively and the average crystallite size (D) is ~70.00nm

FESEM Analysis

Morphological Characterization

The purpose of the FESEM investigation is to look into the average crystallite size and surface morphology of the produced phosphors. The representative FESEM micrographs for synthesized Ba2- xEuxMgSi2O7 (x=0.05) phosphor are shown in Figure 3. The resultant structure, which is comprised of the calculated values of the XRD data, is shown from the FESEM micrographs to have a diameter of roughly 35 nm. The crystallites, which are generated during the combustion synthesis of the samples, are also apparent in the micrographs and are uniformly distributed, occupied angular spaces and pores.

It's possible to have a great deal of unoccupied space even though, when heated rapidly to650oC, a sample containing stoichiometric amounts of redox mixture boils, undergoes dehydration, and then decomposes, producing combustible gases like oxides of N2, H2O, and nascent oxygen. The volatile combustible gases ignite, burn with a flame, and create the idealenvironmentforthedevelopmentofadopedphosphorlattice.Besidesthat, this process enables the uniform (homogeneous) one-step doping of trace amounts of rare-earth   impurity   ions.   The enormous number   of   emitted   gases disperse heat, preventing the material from sintering and creating the ideal environment for the growth of the Nano crystalline phase. The FESEM images clearly shown that the phosphor particles were asymmetrical and constituted Nano clusters. We also anticipate that the particle surface shape may have an impact on the optical characteristics of these phosphor materials.

Figure 3: FESEM Morphology Image of Fascinated Ba2-xEuxMgSi2O7 (x=0.05) Powder Sample.

Thermo luminescence Analysis

The main objective of TL experiments is to collect data from an experimental glow curve, or from a sequence of glow curves, and to analyze that data to determine values of the numerous parameters with respect to the relevant luminescence mechanisms. Thermal release of that trapped electron and recombination with Eu3+then yields the 5d–4f emission of Eu2+as the persistent luminescence. Held to account   werethephosphor'sthermoluminescencecharacteristicswhenexposedtoUVradiation. The TL glow curve was recorded for different exposure time irradiation (5, 10, 15, 20,25min) dose of UV (254nm) radiationofsynthesizedBa2-xEuxMgSi2O7(x=0.05) phosphorus shown in Figure 4, and it was observed that TL intensity is maximum for UVdoseof15minute. Systematically examined and analysed are     the thermal characteristics as expressed by TL glow curves. The observations demonstrate that alterations in concentration of dopant Eu2+ ions have little effect on the peak positions in the spectra. The frequency factor, activation energy or trap depth, order of kinetics (b), and other   trapping   parameters were all estimated using Chen's empirical technique.

Chen's Peak Shape Method

For the analysis of TL parameters including activation energy (E) or trap depth, order of kinetics (b), and frequency factor (s-1), Chen's peak shape approach is extremely well-liked. This is dependent on the dimensions and shape of the TL glow curve and helps identify the different energy levels created by defects and where they are located in the host materials' prohibited energy-gap. This approach is based on Chen's equations, which may be employed to estimate the trapping parameters shown below [15]:

[a]Activation Energy or Trap Depth (E)


Where α is τ, δ, or ω. The values of cα and bα are summarized as below:         

cτ = [1.51+ 3(μg-0.42)], bτ = [1.58+4.2(μg-0.42)]         (4.1)

????????=   [0.976 + 7.3 (????????−0. 42)] , ???????? = 0                            (4.2)

cω = [2.52 + 10.2(μg-0.42)], bω = 1.0                            (4.3)

The TL approach is used to assess the depth of the traps and the density of the trapped carriers. The variations of trap depth with temperature is illustrated in Fig. 5. Table 1 displays the values of several parameters derived from glow curves. Simulations place the value of trap depth, which resembles activation energy, between in the range of 0.57eV to 0.69eV. In accordance with the Chen technique [16], the activation energy with the highest intensity for these glow curves is predicted to be 0.69 eV for a 15- minute UV exposure time, and it also observed that there is no change in TL glow curve shape but the variation of temperature corresponding to TL peak has been observed. On the other hand, it is also established that when the concentration of activator ions falls, so does the amount of energy store by the ions. The activator ion is consequently included within the synthesized compounds at a precise and desirable concentration. Even though of the comparable ionic radii of the two ions, the dopant Eu2+ ions are predicted to substitute into Ba2+ sites and generate the TL intensity.

Inside this Ba2+ sites, such lattice deformation and interaction of the dopant Eu2+ ions'; 4f65d1 orbitals to the deformed lattice are strengthened. The lowest 4f65d1 excited state's energy is reduced by this deformationand interaction with the lattice, creating a narrow energy gap between the excited 4f65d1 state and the 4f7 ground state. As a result, the lowest 4f65d1 excited state emits energy to the 4f7 ground state.

[a]Geometrical Shape Factor (µg) & Order of Kinetics (b)

The value of geometrical shape factor (µg) can be calculated using formula given below:


Where Tm is the temperature corresponding to peak TL intensity, T1 and T2 are temperatures at half the maximum TL intensity. For first order kinetics, µg = 0.39-0.42 and for second orderkinetics, µg= 0.49-0.52 [15].

As mentioned by order of kinetics (b), the values of activation energy and frequency factor with the help of Chen’s τ - equation, Chen’s δ-equation and Chen’s ω-equation can be estimated [15] Where τ = Tm -T1, δ = T2 - Tm, and ω = T2 -T1.

As a consequence, in our instance, we were able to achieve the maximal thermoluminescence [TL] after 15 minutes of UV exposure. In our instance, the geometric shape factor (µg) is between 0.46 to 0.53, implying that second order kinetics, that exists in responsible of deeper trap depth, which supports that they should provide of recapturing liberated charge carriers prior to the recombination mechanism process.

[a] Frequency Factor (s-1)

The preceding mathematical formulation is employed to estimate this trapping parameter by substituting the predetermined values of order of kinetics (b) and activation energy (E).


Where k represents Boltzmann constant, E represents activation energy & b represents an order of kinetics, Tm represents the prominent temperature of glow-curve peak position, and β (i.e. at present work 50Cs-1) represents the heating rate of the any material sample [17-20].

Analysis of TL glow curve

A proper investigation of the TL glow curve is performed in order to figure out the trapping parameters (activation energy, frequency factor, order of kinetics, etc.). Analysis of the TL glow curve reveals whether the materials are suited for TL dosimetry or not. Inside this analysis, a constant heating rate of 5oCs-1 was employed in order to measure the TL glow curve. In accordance with a viable combustion synthesis technique, Fig. 4 depicts the TL glow curve of a synthesized Ba2MgSi2O7:Eu2+ phosphor with varying UV radiation exposure times for a 5 mol% concentration of doping concentration of Eu2+ ions. It is observed that initially on increasing the doping concentration of Eu2+ ions, TL intensity increases and optimum intensity is attained for 5 mol% of Eu2+ at 102.21oC, after that concentration quenching occurs, which results in decrease in TL intensity with increasing dopant concentration. The TL glow curve of fascinated Ba2-xEuxMgSi2O7 (x=0.05) phosphor was shown symmetrical and the peak positionof all TL peaks for various UV exposure time such as 5min, 10min, 15min, 20min, 25min of dopant Eu2+ ions give nearly similar glow peak at 102.21oC.

Figure 4: TL Glow Curve of Ba2-xEuxMgSi2O7 (x=0.05) Phosphor with different UV radiation exposure time.

The TL intensity is found to be an effective activator ion in such phosphors and is greatly reliant on the dopant concentration (Eu2+). The maximum concentration of dopant Eu2+ ions were 5 mol%. After that, it was exposed to various UV exposure times, and it was predicted that as exposure time increased, the TL intensity would rise up to 15 min before decreasing with further UV exposure (Figure 4). Depending on, we can infer that the trapped level may have started to decrease, that also led to a decrease in thermos luminescence signals.

Figure 4 illustrates that the TL glow curve of Ba2-xEuxMgSi2O7 (x=0.05) phosphor utilized for peak shape method. All trapping parameters such as order of kinetics (b), activation energy (E) and frequency factor (s−1) were calculated by using Chen’s peak shape method and the corresponding values are enlisted Table 1. In our case, the frequency factor (s−1) is lies between1.2 × 106 s-1 to 9.8 × 107 s-1.

Table 2: Kinetic parameters of UV-irradiated Ba2-xEuxMgSi2O7 (x=0.05) phosphor.


UV Exposure Time


T1 (oC)


Tm (oC)


T2 (oC)













Activation Energy E



Frequency Factor (s-




















































According to Sakai’s and Mashangva report, a trap depth between 0.65 − 0.75 eV is very appropriate for long afterglow properties [21,22]. The combustion synthesis method was usedto fascinate Ba2-xEuxMgSi2O7 (x=0.05) phosphor, which effectively indicates the phosphor's superior amount of persistency in its thermoluminescence characteristic. We have suggested that this synthesized Ba2-xEuxMgSi2O7 (x=0.05) phosphor is an excellent TL material and a more efficient long persistence luminescent material.






Using a combustion synthesis technique, Ba2-xEuxMgSi2O7 (x=0.05) phosphor was successfully fascinated. JCPDS file #23- 0842 have used to have a decent match with the phosphor's XRD pattern. The sintered phosphor was obtained in Nano-range with much better homogeneity. The synthesized phosphor exhibits Nano crystalline behavior and strong connection with grain, which indicates that powder size and shape are tightly controlled, according to the FESEM images. The XRD patterns and FESEM micrographs revealed no discernible change; as a result, synthesized materials are effectively crystallized into monoclinic Ba2MgSi2O7: Eu2+ crystal structures. TL glow curve of synthesized phosphor with 5mol% doping concentration of Eu2+ ions, with different UV exposure time (i.e. 5, 10, 15, 20,25min) at constant heating rate 5oCs−1 have been investigated. It was eventually determined that 15 minutes of UV exposure is the maximum amount of time for the TL intensity to occur. TL glow curve revealed a significant peak assigned at 102.21oC, respectively. In our instance, a very strong TL glow curve peak for this synthesized phosphor was observed. Second order kinetics was illustrated by the TL glow curve, which is responsible for deeper trap depth. The TL-intensity rises as the concentration of Eu2+ ions rises, reaches its maximum value, and then declines, when Eu2+ ions concentrations rise in the afterwards due to the concentration quenching. Due to trap level may have started to destroy, resulting in decrease in thermo luminescence signals. The dopant [Eu2+] ions can work as both luminescence center and traps. According to calculated trap depth, the synthesized phosphor is an efficient persistent luminescent material.


Our comprehension of the mechanism will determine how to exploit the innovative illuminating materials. The important role of TL radiation dosimeter is apparent in an extensive variety of fields, along with medical dosimetry, environmental radiation monitoring, biology, neutron dosimeter, reactor engineering, high level photon dosimetry with TL materials, standardization and inter comparison of TL dosimeters used in personnel monitoring, as well as archaeological dating, mineral prospering, long persistent phosphor, forensic science, and radiation dosimetry.




Authors are very grateful to Department of Physics, Dr. Radha Bai, Govt. Navin Girls College, Raipur (C.G) India for support material preparation in experimental research work. We are alsothankful to kind support NIT Raipur (C.G.) for XRD, & FESEM facility and Pt. Ravishankar Shukla University, Raipur (C.G.) India for TL facility.

Authors Contributions

Both authors contributed to the completion of this work. Author Dr. Shashank Sharma undertakes the manuscript designed and conducted the entire experiments & characterization studies, collected and analyzed the research data findings, and prepared the entire manuscript draft as well as supervised the results-discussion. Similarly, author Dr. Sanjay Kumar Dubey has properly checked the spelling mistake, punctuation, grammatical error, conceptualization, and helped in sample preparation. The final article was proofread and approved by both contributors.

Conflict of Interest

In our current research work, there are no potential conflicts of interest or financial conflicts.


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