Thermoluminescence Study of Prepared Ba2 MgSi2 O7: Eu2+, Dy3+ Nano Phosphor via Combustion Synthesis Technique (CST)
Sharma S and Dubey SK
Published on: 2024-05-15
Abstract
Here, we have discussed that the thermal characteristics of well fascinated Ba2 MgSi2 O7: Eu2+, Dy3+ nano phosphor via combustion synthesis technique (CST) at the already well-maintained muffle furnace temperature at 6500C for 5min, and post annealed at 10000C for 2hours. Synthesized powder sample was further analysed for thermal properties with using Nucleonix (Hyderabad, India) Pc based TLD Reader (TL 1009I) with obtained thermoluminescence (TL) glow peak curves were plotted at room temperature. It has been identified that it contains a single prominent peak at 100.12°C temperature from TL glow curve. All the kinetic or trapping parameters such as activation energy [E], order of kinetics [b], and frequency factor [S] of trap centre of the fitted thermoluminescence (TL) glow curves of the synthesized powder samples were examined at different UV exposure times via Chen’s empirical formula. The position of the TL peak shifts towards optimum temperature, indicating the considerable retrapping associated with general order kinetics (b). The depths of the trap were found to between in the range of 0.62 to 0.76eV. The prepared phosphor shows potential application as per long persisting behaviour. We have proposed that the combined phosphor is a more efficient thermoluminescent material.
Keywords
Ba2 MgSi2 O7: Eu2+, Dy3+; Thermoluminescence (TL); Combustion synthesis technique (CST)Introduction
The foundation of nanotechnology can be traced back to the ideas and concepts proposed by the American physicist and Noble Prize laureate Richard Feynman in his famous lecture titled "There's Plenty of Room at the Bottom" in the year of 1959 [1]. Feynman envisioned the manipulation and control of matter at the atomic and molecular levels. Over the years, advancements in various fields such as chemistry, physics, and materials science led to the development of nanotechnology. “Nano” indicates the range in Nano-level (i.e. 10-9). The prefix “Nano” is taken from the Greek language, whose meaning is “extremely small” [2]. Therefore, the term “Nano material” or “Nano crystalline material” refers to a substance whose physical dimension that range is between 0.1 nm and 100 nm in scale [3]. Silicate-based phosphors have attracted much attention because of their many advantages compared with previously developed aluminate materials, the silicate phosphors have more advantages such as high thermal, chemical stability, heat stability, and lower cost, and excellent water resistance, colour variety [4]. The crystalline structure of host (Ba2 MgSi2 O7) is monoclinic form, having a space group of [5]. SiO4 and MgO4 tetrahedral layers in two dimensions are joined by shared corners. Eight oxygen ions collaborate with each other to coordinate between both the Ba2+ ions that also are located layers [6]. In previous literatures, M2MgSi2O7 (Sr, Ca, Ba) doped with Eu2+ and Dy3+ phosphor has shown more efficient and good long persisting behaviour. Generally, in Eu2+ and Dy3+ co-doped systems, the Eu2+ acts as the luminescent centre and the Dy3+ to produce some traps for electrons or holes [7]. The traps in the long afterglow phosphor are very plentiful, which result in the long afterglow [8] process. According to a “hole transfer model”, put forward by Matsuzawa et al., it was stated that Eu2+ ions served as electron traps (Eu2+ + e → Eu+) while Dy3+ ions served as hole traps (Dy3+ + hole → Dy4+). Between the lower energy state (ground) and higher energy state (excited) state of Eu2+ ions, and Dy3+ ions serve as deep hole trap levels [9]. It is anticipated that the co-dopant [Dy3+] ions generate deeper traps in host lattice crystal site. Because the defect level formed by Dy3+ ions is deeper. Co-dopant [Dy3+] ions enhance the persistent luminescence obtained with Eu2+ doping alone. On the basis of, we may conclude that the deeper traps are highly beneficial for enhancing the afterglow process and its long-lasting endurance for completely releasing captured holes or electrons.
TL is the emission of light from a solid, either inorganic, semiconductor or insulator in form, when it is heated after exposure to some radiation [10,11]. From the TL glow curve of prepared Ba2 MgSi2 O7: Eu2+, Dy3+ phosphor, it was observed that single broad peak exists at 100.12°C. To determine the trapping parameters or the kinetic parameters which mainly comprise such as Order of Kinetics [b] and Frequency Factor [S] as well as Activation Energy or Trap Depth [E], Chen’s peak shape method is being used. In this research article, Ba2 MgSi2 O7: Eu2+, Dy3+ phosphor with the concentration ratios of dopant (0.5mol %) and co-dopant (2mol %) were pre-pared using conventional combustion synthesis technique (CST). Thermoluminescence (TL) glow curve with trapping parameters have measured to estimate the persistency of the prepared phosphor.
Experimental Details
Combustion Synthesis Technique (CST)
This technique appears to meet the demands of Material Science and Engineering in tailor making materials with desired composition, structure and its versatile features. This technique is well suitable to the synthesis of nanomaterials in the range of 1–100 nm. The combustion synthesis technique is a facile, fast, versatile, cheaper and efficient pathway for rapid production of a broad range of oxides, ceramics, catalysts and Nano-sized phosphor materials from a technology point of view [5,12,13]. In combustion technique two important mediums are involved, one is oxidizer and other is fuel. This technique additionally has the potential to improve materials, energy conservation, and environment protection. Key advantages of combustion process as well as several prospective benefits, include cheaper, energy efficiency, and high production rate [14]. In this present investigation, urea (NH2 CONH2) is used as fuel and all metal nitrates are used as oxidizers during material synthesis process.
Sample Preparation
We have used combustion synthesis process in our experiment [fig.1] for the preparation of Ba2 MgSi2 O7: Eu2+, Dy3+ Nano phosphor. With (99.99%) purity, Ba (NO3)2 ? 6H2O (AR), Mg (NO3)2 ? 6H2O (AR), SiO2 ? H2O (AR), and rare earth nitrate Dy (NO3)3 ? 5H2O (AR), Eu (NO3)3 ? 5H2O (AR) as well as little amount of distilled ionized water were utilized as starting raw materials, while urea (NH2 CONH2) was used as a combustion fuel and H3BO3 (boric acid) was also used as a flux [5]. Ingredients of the above compound were mixed according to stochiometric ratio in agate mortar and a pasty solution was formed, and the solution was then transfer to silica crucible. The mixture was subsequently heated in already maintained muffle furnace at a constant temperature 650oC. The entire combustion synthesis process got completed in approximately 5min. After a few minutes, the mixture solution undergoes thermal dehydration with release of gaseous products, to form silicates and ignites to produce a self-propagating flame. After next few seconds post its completion, the crucible is taken out of furnace and kept in open for it to be cooled. After cooling, we obtain foamy form of phosphor, which is then grinded with the help of agate mortar pestle to obtain material in the powder form [6,15]. The final product obtained was post-annealed at 1000°C for 2 hours under a weak reducing atmosphere (i.e. using activated charcoal). Using additional crushing to get fine powder. Then powder was collected in airtight bottle for thermo luminescence (TL) characterization study. The chemical reaction of this entire process as follows:
Ba (NO3)2 ? 6H2O + Mg (NO3)2 ? 6H2O + SiO2 ? H2O + NH2CONH2 + H3BO3 ® Ba2MgSi2O7 + H2O (↑) + CO2 (↑) + N2 (↑) (1)
Ba (NO3)2 ? 6H2O + Mg (NO3)2 ? 6H2O + SiO2 ? H2O + Eu (NO3)3 ? 5H2O + Dy (NO3)3 ? 5H2O + NH2 CONH2 + H3 BO3 ® Ba2 MgSi2 O7: Eu3+, Dy3+ + H2O (↑) + CO2 (↑) + N2 (↑) (2)
Figure 1: Systematic Diagram of Material Preparation Process.
Characterization Study
Resulting powder sample was irradiated with UV source for thermoluminescence (TL) analysis. With using Nucleonix (Hyderabad, India) Pc based TLD Reader (TL 1009I) thermoluminescence (TL) glow peak curves were plotted at room temperature.
Results and Discussion
We pick up data with regard to the inter-atomic distance as well as ionic diameters (i.e. radii) from Shannon’s research article, which was proposed in 1976 [26]. In host crystal lattice (Ba2 Mg Si2 O7) dopant [Eu2+] ions dopant [Dy3+] ions are anticipated to substitute Ba2+ sites, on the grounds that the coordination number of Ba2+ ions is eight, Mg2+ and Si4+ ions are four [15]. Tetrahedral [MgO4] or [SiO4] lattice is complicated for them all to Eu2+ and Dy3+ ions incorporate, but octahedral [BaO8] is easily provide it. This seems to be primarily due to ionic radius of Eu2+ (1.12Å) and Dy3+ (0.97 Å) is very near about to Ba2+ (1.42 Å) cations. However, we additionally notice that the ionic-radius of Mg2+ (0.58 Å) & the ionic-radius of Si4+ (0.26 Å) cations are extremely small.
TL Characteristics of Synthesized Phosphor
The thermoluminescence (TL) approach is used to assess the depth of the traps and the density of the trapped carriers. The occurrence in which a substance that has been heated emits light, that has been previously stimulated is also referred to as thermoluminescence (TL) [6,11,22,23]. The long afterglow characteristics of thermo-luminescent phosphor, also known as persistent luminescence, are extremely useful in a many different applications such as emergency lights, safety indicators, road signal, glossy paints, graphic art pieces etc [16]. In Table 2, TL spectra shown displays maximum intensity when Eu: Dy was 0.5: 2, after it starts decreasing in TL intensity. The coupling or deposition of activator ions might have produced quenching centres, which appears due to for decrease in TL intensity after a specific concentration of Dy3+ ions [17].
Table 2: Doping and Co-doping Concentrations of Prepared Phosphors.
Name of Phosphor |
Doping |
Co- doping |
Doping Concentration (in mol %) |
|
Doping |
Co-doping |
|||
Ba2MgSi2O7: Eu2+, Dy3+ |
Eu |
Dy |
0.5 |
2 |
For various UV exposures time, such as 5, 10, 15, 20, 25 and 30 minutes, the TL spectra of the Ba2 MgSi2 O7: Eu2+, Dy3+ phosphor is shown in Fig. 2, and it is shown that the thermoluminescence signals increases with increasing UV exposure. The present circumstance implies a rise in TL intensity of up to 15min depending on the UV irradiation exposure. Time, afterwards which it falls gradually as a consequence of the population’s amount of trapped charge carriers attaining its maximum amount at a particular time in a metastable condition. Trap level may have started to destroy, resulting in decrease in thermoluminescence signals. It has been identified that it contains a single prominent peak at 100.12°C temperature from TL glow curve. The traps are released when the phosphor is heated, and the intensity of the thermoluminescence is raised by radiative recombination at the Dy3+ ions [17].
Figure 2: TL Glow Curve of Ba2 MgSi2 O7: Eu2+, Dy3+ Phosphor after different UV exposure times.
Kinetic/Trapping Parameters
There are various methods for determining the kinetic/trapping parameters from TL glow curves. For example, when one of the TL glow peaks is highly isolated from the others, the experimental method such as peak shape method is suitable to determine kinetic parameters [11]. For estimating the significance of the TL kinetic/trapping parameters such as activation energy [E], order of kinetics [b], and frequency factor [S] for the prominent glow peak of prepared powder samples were calculated with the help of Chen’s peak shape empirical formula [18,19].
Order of Kinetics [b]
Order of kinetics depends on the peak shape of TL glow curve. The mechanism of recombination of de-trapped charge carriers with their counterparts is known as the order of kinetics (b) [11]. The kinetic order for glow peak of as-synthesized Ba2 Mg Si2 O7: Eu2+, Dy3+ phosphor may be figure out via calculating geometrical shape factor (µg) from the mathematical relation as follows:
(3)
where Tm symbolize the optimum temperature, T1 & T2 symbolizes the temperatures at half intensity on the ascending and descending parts of the TL glow peak curve, respectively, [ω = T2–T1], the optimum-temperature half width [δ = T2 – Tm] maxima (FWHM). Remarkably, the shape factor (μg), spanning from 0.49 to 0.50, which is extremely near about the value of the second order kinetics [i.e. µg = 0.49-0.52]. The value of shape factor varied from 0⋅49 to 0⋅53, which indicate the second order kinetics that support the probability of retrapping released charge carriers before recombination process [6,11,20].
Activation Energy [E]/Trap Depth
Thermoluminescence is one of the possible ways to estimate the trap states of the material. For the purpose of determining the value of trap depth/activation energy [E], we utilised the aforementioned formula [6,11,22]:
The values of the Cα and bα (α = τ, δ, ω) are expressed as for general order kinetics (b) following as [11]:
cτ = [1.51 + 3(µg – 4.2), bτ = [1.58 + 0.42 ((µg – 0.42)]; cδ = [0.976 + 7.3 (µg – 0.42)], bδ = 0 and cω = [2.52 + 10.2 (µg – 0.42)], bω = 1.0.
Frequency Factor (S)
This kinetic parameter is one of the most significant parameters which are used for the sample characterization process [11,22,23]. This trapping parameter is calculated by substituting the previously evaluated values of order of kinetics [b] and activation energy [E] in the mathematical equation (as mentioned):
Where Boltzmann constant is denoted by k, Tm the temperature of peak position, b symbolizes the order of the kinetics that is the value is equal of two in the present case, and β is the linear heating rate. Β = 5°Cs–1, Table 2 depicts the trapping or kinetic parameters for depth or activation energy € and frequency factor (s) at the room temperature, which were determined employing this equation (3-5).
Table 2: Kinetic/Trapping Parameters of Ba2 MgSi2 O7: Eu2+, Dy3+ Phosphor at different UV exposure time.
UV Exposure Time |
β (?s-1) |
T1 (?) |
Tm (°C) |
T2 (°C) |
T |
δ |
ω |
µg = δ/ω |
E (eV) |
Frequency Factor (S-1) |
5min |
5 |
72.67 |
100.12 |
126.79 |
27.45 |
26.67 |
54.12 |
0.49 |
0.62 |
1.03 × 107 |
10 min |
5 |
76.49 |
100.12 |
126.79 |
23.63 |
26.67 |
50.31 |
0.53 |
0.76 |
1.5 × 107 |
15 min |
5 |
72.67 |
100.12 |
126.79 |
27.45 |
26.67 |
54.12 |
0.49 |
0.62 |
1.03 × 107 |
20 min |
5 |
76.49 |
100.12 |
124.79 |
23.63 |
24.67 |
48.3 |
0.49 |
0.7 |
1.3 × 107 |
25 min |
5 |
74.48 |
100.12 |
124.79 |
25.64 |
24.67 |
50.31 |
0.49 |
0.67 |
1.2 × 107 |
30min |
5 |
73.59 |
100.12 |
126.79 |
26.79 |
26.65 |
52.21 |
0.51 |
0.74 |
1.4 × 107 |
Table 2 depicts that the different parameters derived from Chen’s glow curve method regarding the Ba2 MgSi2 O7: Eu2+, Dy3+ phosphor. Corresponding, Frequency factor (s-1) was calculated in the range between (1.03 × 107 to 1.5 ×107 s-1) respectively. The range of values of 0.62 to 0.76 eV has been determined for trap depth or activation energy, indicating that the sample indicates an increased amount of persistency with regard to its thermoluminescence characteristics. In accordance with the reports that the materials have to demonstrate long persistence properties at a value of depth of trap/activation energy [E] spanning between 0.65 to 0.75 eV [11,24,25]. It is anticipated that deeper trap depths would result in extended afterglow durations and a longer duration for completely releasing captured holes or electrons. Meanwhile, heating of the phosphor sample leads to de-trapping of the traps. As a result, the radiative recombination mechanism on co-dopant [Dy3+] ion gives rise to the TL stimulation process [11]. As a result, Dy3+ ion generates deeper traps in host lattice crystal site. Because the defect level formed by Dy3+ ions is deeper. Deeper traps can enhance the stability of the luminescent centers, preventing them from deactivating quickly and thereby increasing the afterglow duration and persistence, allowing for more light emission.
Conclusion
In summary, Europium (Eu2+) doped and Dysprosium (Dy3+) codoped Ba2 MgSi2 O7 nanocrystalline phosphor was well synthesized using the conventional combustion synthesis technique and further characterized by the employing of thermoluminescence [TL] analysis. In TL analysis, single broadband glow curve peak was observed at 100.12°C. Corresponding, Frequency factor (s-1) was calculated in the range between (1.03 × 107 to 1.5 × 107 s-1) respectively. The probability of liberated charge carriers could potentially be re-trapped prior to recombination occurs is supported by second order kinetics. It becomes apparent that the phosphor's trap depths energy ranges from 0.62 eV to 0.76 eV for ultraviolet (UV) exposure times between 5 minutes to 30minutes, correspondingly, which is very appropriate and favourable for long afterglow properties. Consequently, deeper traps are created in the host lattice crystal by Dy3+ ions. Based on this, we may conclude that deeper traps are highly beneficial for extending the afterglow process and its long persistency. It is considered that this asprepared phosphor sample is highly applicable for long persistent phosphor and outstanding candidate for thermoluminescent material.
Acknowledgements
Authors are very grateful to Dept. of Physics, Dr. Radha Bai, Govt. Navin Girls College, and Raipur (C.G) for support in experimental research work. We are also thankful to Pt. Ravishankar Shukla University, Raipur (C.G.) India for kind support in thermoluminescence (TL) characterization study. This research work is also based on unpublished research data during Ph.D., which is experimental work done between 2018 to 2022.
Credit Authorship Contribution Statement
Dr. Shashank Sharma: Conceptualization, Methodology, Formal analysis, Investigation, Writing – original draft.
Dr. Sanjay Kumar Dubey: Preparation Material Sample, Paper Design, Results-Discussion, Properly Checked the Spelling Mistake and Grammatical Error.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Author’s Agreement
We certify that each author has reviewed and approved the completed manuscript before it is submitted. The article is our original work, not being considered for publication elsewhere or having been published before.
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