- Email: [email protected]
Low temperature salt melt synthesis, thermal and optical studies of AZrO3:Eu3+,Tb3+ perovskite phosphors
Journal Pre-proof Low temperature salt melt synthesis, thermal and optical studies of AZrO3 :Eu3+ ,Tb3+ perovskite phosphors Shambhavi Katyayan, Sadhana Agrawal
PII:
S0030-4026(19)32024-8
DOI:
https://doi.org/10.1016/j.ijleo.2019.164125
Reference:
IJLEO 164125
To appear in:
Optik
Received Date:
25 November 2019
Accepted Date:
23 December 2019
Please cite this article as: Katyayan S, Agrawal S, Low temperature salt melt synthesis, thermal and optical studies of AZrO3 :Eu3+ ,Tb3+ perovskite phosphors, Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.164125
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Low temperature salt melt synthesis, thermal and optical studies of AZrO3:Eu3+,Tb3+ perovskite phosphors
Shambhavi Katyayan1 , Sadhana Agrawal 2*
Department of Physics, National Institute of Technology Raipur, Raipur-492010, India
2
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https://orcid.org/0000-0001-6584-7040
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1
* Department of Physics, National Institute of Technology Raipur, Raipur-492010, India
2
-p
https://orcid.org/0000-0003-0364-6053
* Corresponding author. Tel.: +91-9993885860.
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E-mail address: [email protected]
Abstract
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The paper gives a keen insight of thermal and optical characteristics of rare earth impurities doped metazirconate perovskites synthesized by low temperature salt melt technique. The impurity concentration of each rare earth doping ions varies from 0 mol% to 2 mol%. The synthesized perovskites when subjected to crystallographic, morphological, topographical optical and thermal analyses, many interesting characteristics were revealed. The structural analysis confirms the crystalline nature of synthesized perovskites with homogeneity and phase purity. The topographical and morphological studies show formation of particles with distinct morphology, variable shapes and sizes agglomerated into clusters. The thermal analysis indicates the thermal stability of synthesized perovskites with less weight loss%. The study of thermoluminescent (TL) behavior of synthesized perovskite phosphors set forth the second order kinetics, deep trapping mechanism and high value of activation energy exhibited by these phosphors. Keywords: Perovskites; Phosphors; Thermoluminscence; Activation energy; Trap depth ; Order of kinetics. 1. Introduction
The synthesis of highly efficient thermally stimulated luminescent (TSL) materials for radiation detection, exposure assessment, monitoring, etc. applications have revolutionized the research domain from last few decades. The sensitivity to radiation exposure, linear and spatial dose assessment, etc. is some crucial characteristics of efficient TSL materials. The TSL material exhibit luminescence when treated thermally after pre-exposure to ionizing radiations. The phenomenon of thermoluminescence can be explained by a number of models but the simplest and mostly preferred is- One trapping centre and recombination (OTOR) model. When the electrons of TL material exposed to ionizing radiation get enough energy to overcome the band gap, ionization of electrons takes place resulting into generation of free electrons and holes in the material. Most of these free electrons and holes get
1
trapped in their respective electron and hole trapping sites or trap centers [1]. The probability per unit time of release of electrons from the trapping sites when subjected to thermal stimulation is given by Arrhenius eqn.𝐄
𝐩 = 𝐬𝐞−(𝐊𝐓)
of
Where, s gives the escape factor or frequency factor. It is a constant with its value in the order of 10-12 to 10-14 sec-1. Besides frequency factor s, one more crucial parameter that governs the TL characteristics of a material is trap depth or activation energy E (eV). It gives the amount of energy required to release an electron from its trapping site into the conduction band. The thermal treatment leads to de-trapping of electrons and holes followed by their recombination with their respective counterparts [2]. With increase of thermal stimulation temperature, the process of de-trapping and recombination can be paced up. But increasing the thermal stimulation temperature beyond a specific value i.e. critical temperature T0 is not beneficial as an increase of temperature beyond T0 leads to diminution of quantum yield due to thermal quenching. As proposed by Randall and Wilkins, the recombination center is a luminescent center where recombination of electrons and holes takes place followed by release of energy resulting into thermoluminescence. But every recombination does not result into radiative transition or luminescence, a few of them may results into non-radiative transitions or lattice vibrations (phonons) [3].
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2. Experimental
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The AZrO3:Eu3+,Tb3+ (A= Ca, Ba, Sr) phosphors were synthesized using the metal carbonates of calcium, barium and strontium, ACO3 (A= Ca, Ba, Sr), ZrO2, Eu2O3 and Tb2O3 (99.99 %) supplied by Sigma Aldrich as the primary reactants. These constituents taken in exact stoichiometric ratio along with fused salt NaCl were finely ground before sintering for 4 hr at 950oC. The solid melt obtained after sintering is washed repeatively with hot distilled water to remove the traces of salt from the synthesized phosphors[4]. This mixture is annealed for 6 hrs at 150oC, so that it restores the fine ceramic characteristics. CaCO3 → CaO + CO2
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CaO + ZrO2 + Eu2O3 + Tb2O3 → CaZrO3∶Eu3+, Tb3+ BaCO3 → BaO + CO2
ur na
BaO + ZrO2 + Eu2O3 + Tb2O3 → BaZrO3∶Eu3+, Tb3+ SrCO3 → SrO + CO2
SrO + ZrO2 + Eu2O3 + Tb2O3 → SrZrO3∶Eu3+, Tb3+
The synthesized perovskites were subjected to various structural, morphological, topographical, optical and thermal analyses.
Jo
3. Crystallographic analysis
The structural characteristics and crystallographic parameters were studied from the recorded PXRD patterns of synthesized perovskites. Here, 3W PANalytical-XPERT Powder X-ray diffractometer (PXRD) was used for mapping the PXRD patterns as shown in figure 1. It uses the X-ray beam (λ= 0.154 nm) generated by the Cu-anode, to obtain the diffraction patterns obtained for analysis [5].
2
3000
30
20
80
70
60
50
40
3+
SrZrO3:Eu , Tb
3+
(002) 2000
(110) (111)
(420)
(021) (040)
1000
(242) (323) (310)
(240)
3+
BaZrO3:Eu , Tb
3000
3+
(001) (100)
2000
(101) (002) (200) (111)
1000
8000
(102) (112) (220) (310) 3+
CaZrO3:Eu , Tb
(121)
of
INTENSITY ( A.U)
4000
3+
(202) (111)
2000 20
30
(042) (242)
(130) (103) 50
40
60
70
(034)
80
-p
4000
ro
6000
2 Theta (angle)
a (Å)
b (Å)
c (Å)
α,𝞫,γ
Pcmn
7.90
5.60
7.10
Cubic
Pm3m
4.80
5.55
12.5
Orthorhombic
Pcmn
12.8
7.30
10.9
α = 70o 𝞫= 100 o γ = 98o α = 90o 𝞫= 90 o γ = 90o α = 90o 𝞫= 112o γ = 90o
Crystal structure
CaZrO3: Eu3+, Tb3+ (1:1 mol%)
76-2401
Orthorhombic
BaZrO3: Eu3+, Tb3+ (1:1 mol%)
06-0399
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JCPDS card no.
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Phosphors
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Fig 1. PXRD pattern of AZrO3:Eu3+,Tb3+ phosphors
SrZrO3: Eu3+, Tb3+ (1:1 mol%)
44-0161
Space group
Table 1. Crystallographic parameters of AZrO3:Eu3+,Tb3+ phosphors
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The crystallographic studies confirm crystalline structure with homogeneity and phase purity of the synthesized perovskites. No additional peaks of impurity ions were obtained. The table 1 shows crystallographic parameters of AZrO3:Eu3+,Tb3+ and ATiO3:Eu2+,Yb2+ (A=Ca, Ba, Sr) perovskite phosphors [6].
4. FESEM and TEM analyses The topographical and morphological analysis were done here using JEOL-JSM-5200 operating at 20 KV and JEOL JEM 2100 operating at 200 KV respectively.
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(a) (b) Fig 2. FESEM micrographs (a) and (b) of AZrO3:Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
(a) (b) 3+ 3+ Fig 3. TEM micrographs (a) and (b) of AZrO3: Eu ,Tb (A=Ca, Ba, Sr) phosphors
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The FESEM micrographs in Fig. 3 show clusters of particles agglomerated in clumps with shape and sizes. The TEM micrographs in Fig. 4 also well agree with the distinct topography revealed in FESEM analysis [7]. The FESEM micrographs show clusters of particles with irregular shape and variable sizes agglomerated in clusters. The long duration heat treatment sessions at elevated temperatures followed by pro-longed annealing result in agglomeration of the particles [8]. 5. Thermogravimetric Analysis The Thermogravimetric Analysis (TGA) done by using TGA 4000 Pyris 6 TG analyzer in the gaseous atmosphere of nitrogen gas at 20 ml/min. The perovskites per subjected to heat treatment from 30oC to 700oC for study of thermal characteristics. The perovskites exhibit less weight loss% confirming their stability towards thermal invariance. The average weight loss% of 4.51, 3.47 and 11.90% was obtained for CaZrO3:Eu3+,Tb3+, BaZrO3:Eu3+,Tb3+ and SrZrO3:Eu3+,Tb3+ respectively as shown in figure 4 [9].
4
3+
3+
3+
BaZrO3:Eu ,Tb (1,1 mol%)
3+
CaZrO3:Eu ,Tb (1,1 mol%) 100 102
Delta W (%)
Delta W (%)
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100 96 400
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Sample Temperature (K)
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Sample Temperature (K) 3+
3+
SrZrO3:Eu ,Tb (1,1 mol%)
of
100
96 94 92 90 88 800 700 600 500 Sample Temperature (K)
900
1000
-p
400
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Delta W (%)
98
Fig 4. TGA curves of AZrO3: Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
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The maximum weight loss% of 11.90% of SrZrO3:Eu3+,Tb3+ indicates that these perovskites were less thermally stable than the other perovskites [10].
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6. Thermoluminescent Study of AZrO3: Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
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The thermoluminescent behavior of synthesized perovskite phosphors pre-exposed to ionizing radiations were studied using TL/OSL Reader 1008 supplied by Nucleonix Systems. The recorded thermograms were deconvoluted and analyzed using Glowfit and TLanal software for estimation of kinetic parameters [11]. 6.1. Thermoluminescent study of UV irradiated phosphors
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The synthesized perovskites were subjected to UVR irradiation of 254 nm for 5 min at room temperature. The TL glow curves were mapped on heating the irradiated sample from room temperature to 500oC with a constant heating rate of 5oC/s [12].
5
BaZrO3 undoped
CaZrO3 undoped
3+
BaZrO: Tb (1,0mol%)
3+
CaZrO3 : Eu (1mol%)
6000000
3+
BaZrO3 : Eu (1mol%)
3+
CaZrO: Tb (1,0mol%) 3+
3+
3+
4000000
CaZrO3 :Eu , Tb (1,1 mol%)
3+
BaZrO3 :Eu , Tb (1,1 mol%)
TL Intensity (a.u.)
TL Intensity (a.u.)
5000000
4000000
3000000
3000000
2000000
2000000
1000000 1000000
0
0 350
400
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Temperature (Kelvin)
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3+
3+
SrZrO3 :Eu , Tb (1,1 mol%) 3+
ro
SrZrO3 undoped
of
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SrZrO: Tb (1,0mol%)
300000
3+
SrZrO3 : Eu (1mol%)
-p
200000
150000
100000
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TL Intensity (a.u.)
250000
0
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50000
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400
500
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700
Temperature (Kelvin)
Fig. 5 TL glow curves of UV irradiated AZrO3: Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
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The synthesized phosphors exhibit both first and second order kinetics, increased quantum yield along with shallow and deep trapping mechanism as shown in figure 5. The CaZrO3:Eu3+,Tb3+ phosphors have the value of average activation energy as 2.27eV with shallow trapping. The BaZrO3:Eu3+,Tb3+ phosphors show the value of average activation energy of 2.16eV. The SrZrO3:Eu3+,Tb3+ phosphors have second order of kinetics with average activation energy of 3eV. This confirms occurrence of deep trapping in these phosphors [13].
6.2. Thermoluminescent study of γ irradiated phosphors
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The synthesized perovskites were irradiated with γ radiation of 5 Gy for 2.2 mins using Theratron 780E, Teletherapy unit with Co60 as the radiation source. The TL glow curves were mapped on heating the irradiated sample from room temperature to 500oC with a constant heating rate of 5oC/s [14]. The source to surface distance is kept 80 cm in a field of 20 𝗑 20 cm2. The TL responses were mapped using TL/OSL Reader 1008 from room temperature to 500 °C at a heating rate of 10 °C/s. The recorded thermograms as shown in figure 6 were deconvoluted and analyzed using Glowfit and TLanal software for estimation of kinetic parameters [15].
6
BaZrO3 undoped
CaZrO3 undoped
3+
BaZrO3 : Eu (1mol%)
3+
CaZrO: Tb (1,0mol%)
3+
BaZrO: Tb (1,0mol%)
3+
CaZrO3 : Eu (1mol%) 3+
3+
3+
CaZrO3 :Eu , Tb (1,1 mol%)
140000
120000
120000
100000
TL Intensity (a.u.)
80000
60000
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60000
40000
40000
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20000
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0 300
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700
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of
TL Intensity (a.u.)
3+
BaZrO3 :Eu , Tb (1,1 mol%)
140000
Temperature (Kelvin)
Temperature (Kelvin)
ro
SrZrO3 undoped 3+
SrZrO: Tb (1,0mol%) 3+
SrZrO3 : Eu (1mol%)
270000
3+
240000
-p
180000 150000 120000
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TL Intensity (a.u.)
210000
90000 60000
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30000 0
3+
SrZrO3 :Eu , Tb (1,1 mol%)
300
400
500
600
700
800
Temperature (Kelvin)
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Fig. 6 TL glow curve of γ irradiated AZrO3: Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
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The synthesized phosphors exhibit second order kinetics, increased quantum yield along with deep trapping mechanism. The CaZrO3:Eu3+,Tb3+ phosphors have the value of average activation energy as 2.59eV with deep trapping and second order of kinetics [16]. The BaZrO3:Eu3+,Tb3+ phosphors show the value of average activation energy of 2.25eV, second order of kinetics and deep trapping. The SrZrO3:Eu3+,Tb3+ phosphors have second order of kinetics with average activation energy of 3eV. The TL glow curve peaks obtained at higher temperatures indicate the low fading characteristics of these synthesized phosphors [17]. On comparing the TL behavior of both UV irradiated and gamma irradiated samples, it was found that gamma irradiated samples exhibit second order kinetics, deep trapping and low fading characteristics. The glow curve peaks above 500K confirms the low fading behavior of gamma irradiated samples. The TL analysis confirms the competence of synthesized perovskite phosphors for sensing, mapping, radiation detection, exposure assessment and monitoring applications is confirmed through the complete TL behavior analysis [18].
7. Conclusion
The synthesized perovskite phosphors have crystalline nature with appreciable phase purity and homogeneity, which were well confirmed by crystallographic analysis. The distinct morphology and topography of these phosphors were set forth by FESEM and TEM studies. The thermogravimetric or thermal analysis of these phosphors confirms the thermal stability of synthesized perovskites with less weight loss%. The maximum weight loss of 11.90% is obtained for SrZrO3:Eu3+,Tb3+. The thermoluminescent studies of UV irradiated and gamma irradiated samples set forth many interesting traits. These perovskites exhibit both second and first order of kinetics along with deep and shallow
7
trapping both. The TL glow curve peaks obtained at higher temperatures indicate the low fading characteristics of these synthesized phosphors and hence confirms their suitability for mapping, sensing and radiation detection pertinences.
Acknowledgement The authors sincerely acknowledge and thanks STIC Kochi University and Department of energy and environment, National Institute of Technology Tiruchirappalli for providing TEM and TGA analysis facility respectively.
Compliance with ethical standards Conflict of interest: We declare that we have no conflict of interest.
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References
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[1] S. Som, A. K. Kunti, Vinod Kumar, Vijay Kumar, S. Dutta, M. Chowdhury, S. K. Sharma, J. J. Terblans, H. C. Swart, Journal of applied physics 115, 193101 (2014), doi: 10.1063/1.4876316. [2] Shi Ye, Chun-Hai Wang, Xi-Ping Jing, Journal of The Electrochemical Society, 155, 6, J148-J151, 2008. [3] S. Katyayan, S. Agrawal, Journal of Materials Science: Materials in Electronics, https://doi.org/10.1007/s10854-018-9754-0. [4] B. Mari, K.C. Singh, Paula Cembrero-Coca, Ishwar Singh, Devender Singh, Subhash Chand, Displays 34 (2013) 346–351. [5] S. Katyayan, S. Agrawal, Materials today: proceedings 4(8):8016- 8024, DOI:10.1016/j.matpr. 2017.07.139. [6] S. Katyayan, S. Agrawal,Optical Society of America, 2016, paper Th3A.82, https://doi.org/10.1364/PHOTONICS.2016.Th3A.82. [7] Jiapeng Fu,Qinghong Zhang, Yaogang Li, HongzhiWang, Journal of Alloys and Compounds 485 (2009) 418–421. [8]. S. Katyayan, S. Agrawal, Methods Appl. Fluoresc. 6 035002 (2018). [9] Yoshitake Terashi, Agus Purwanto, Wei-Ning Wang, Ferry Iskandar, Kikuo Okuyama, Journal of the European Ceramic Society 28 (2008) 2573–2580. [10] Zhen Xiao, Jiawei Zhang, Lei Jin, Yang Xia, Lei Lei, Huanping Wang, Junjie Zhang, Shiqing Xu, Journal of Alloys and Compounds 724 (2017) 139-145. [11] Yueying Li, Weihua Guo, Hongshun Hao, Lijun Wang, Qing Su, Shanshan Jin, Lei Qin, Wenyuan Gao, Guishan Liu, Zhiqiang Hu, Electrochimica Acta 173 (2015) 656–664. [12] O. Ruzimuradov, G. Hasegawa, K. Kanamori, K. Nakanishi doi: 10.1111/j.1551-2916.2011.04613.x. [13] M. Kuwabara, Journal of Advanced Ceramics , 2012, Vol. 1, Issue (2), 79-88 doi:10.1007/s40145-012-0016-y. [14] Mc Keever S W S,Thermoluminescence of Solids (Cambridge Solid State Science Series) (Cambridge: University Press UK), 1988. -8. [15] S. Katyayan, S. Agrawal, Journal of Materials Science Materials in Electronics, doi:10.1007/s10854-017-7791 [16] Daniel D J, Annalakshmi O, Madhusoodanan U, Ramasamy P, J. Rare Earths 32 496–500, 2014. [17] S. Katyayan, S. Agrawal, Journal of Materials Science Materials in Electronics, doi: 10.1007/s10854-017-8156-z. [18] Horowitz Y S and Yossian D, Radiat. Prot. Dosim. 60 293–5, 1995.
8
PII:
S0030-4026(19)32024-8
DOI:
https://doi.org/10.1016/j.ijleo.2019.164125
Reference:
IJLEO 164125
To appear in:
Optik
Received Date:
25 November 2019
Accepted Date:
23 December 2019
Please cite this article as: Katyayan S, Agrawal S, Low temperature salt melt synthesis, thermal and optical studies of AZrO3 :Eu3+ ,Tb3+ perovskite phosphors, Optik (2019), doi: https://doi.org/10.1016/j.ijleo.2019.164125
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.
Low temperature salt melt synthesis, thermal and optical studies of AZrO3:Eu3+,Tb3+ perovskite phosphors
Shambhavi Katyayan1 , Sadhana Agrawal 2*
Department of Physics, National Institute of Technology Raipur, Raipur-492010, India
2
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https://orcid.org/0000-0001-6584-7040
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1
* Department of Physics, National Institute of Technology Raipur, Raipur-492010, India
2
-p
https://orcid.org/0000-0003-0364-6053
* Corresponding author. Tel.: +91-9993885860.
lP
re
E-mail address: [email protected]
Abstract
Jo
ur na
The paper gives a keen insight of thermal and optical characteristics of rare earth impurities doped metazirconate perovskites synthesized by low temperature salt melt technique. The impurity concentration of each rare earth doping ions varies from 0 mol% to 2 mol%. The synthesized perovskites when subjected to crystallographic, morphological, topographical optical and thermal analyses, many interesting characteristics were revealed. The structural analysis confirms the crystalline nature of synthesized perovskites with homogeneity and phase purity. The topographical and morphological studies show formation of particles with distinct morphology, variable shapes and sizes agglomerated into clusters. The thermal analysis indicates the thermal stability of synthesized perovskites with less weight loss%. The study of thermoluminescent (TL) behavior of synthesized perovskite phosphors set forth the second order kinetics, deep trapping mechanism and high value of activation energy exhibited by these phosphors. Keywords: Perovskites; Phosphors; Thermoluminscence; Activation energy; Trap depth ; Order of kinetics. 1. Introduction
The synthesis of highly efficient thermally stimulated luminescent (TSL) materials for radiation detection, exposure assessment, monitoring, etc. applications have revolutionized the research domain from last few decades. The sensitivity to radiation exposure, linear and spatial dose assessment, etc. is some crucial characteristics of efficient TSL materials. The TSL material exhibit luminescence when treated thermally after pre-exposure to ionizing radiations. The phenomenon of thermoluminescence can be explained by a number of models but the simplest and mostly preferred is- One trapping centre and recombination (OTOR) model. When the electrons of TL material exposed to ionizing radiation get enough energy to overcome the band gap, ionization of electrons takes place resulting into generation of free electrons and holes in the material. Most of these free electrons and holes get
1
trapped in their respective electron and hole trapping sites or trap centers [1]. The probability per unit time of release of electrons from the trapping sites when subjected to thermal stimulation is given by Arrhenius eqn.𝐄
𝐩 = 𝐬𝐞−(𝐊𝐓)
of
Where, s gives the escape factor or frequency factor. It is a constant with its value in the order of 10-12 to 10-14 sec-1. Besides frequency factor s, one more crucial parameter that governs the TL characteristics of a material is trap depth or activation energy E (eV). It gives the amount of energy required to release an electron from its trapping site into the conduction band. The thermal treatment leads to de-trapping of electrons and holes followed by their recombination with their respective counterparts [2]. With increase of thermal stimulation temperature, the process of de-trapping and recombination can be paced up. But increasing the thermal stimulation temperature beyond a specific value i.e. critical temperature T0 is not beneficial as an increase of temperature beyond T0 leads to diminution of quantum yield due to thermal quenching. As proposed by Randall and Wilkins, the recombination center is a luminescent center where recombination of electrons and holes takes place followed by release of energy resulting into thermoluminescence. But every recombination does not result into radiative transition or luminescence, a few of them may results into non-radiative transitions or lattice vibrations (phonons) [3].
ro
2. Experimental
re
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The AZrO3:Eu3+,Tb3+ (A= Ca, Ba, Sr) phosphors were synthesized using the metal carbonates of calcium, barium and strontium, ACO3 (A= Ca, Ba, Sr), ZrO2, Eu2O3 and Tb2O3 (99.99 %) supplied by Sigma Aldrich as the primary reactants. These constituents taken in exact stoichiometric ratio along with fused salt NaCl were finely ground before sintering for 4 hr at 950oC. The solid melt obtained after sintering is washed repeatively with hot distilled water to remove the traces of salt from the synthesized phosphors[4]. This mixture is annealed for 6 hrs at 150oC, so that it restores the fine ceramic characteristics. CaCO3 → CaO + CO2
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CaO + ZrO2 + Eu2O3 + Tb2O3 → CaZrO3∶Eu3+, Tb3+ BaCO3 → BaO + CO2
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BaO + ZrO2 + Eu2O3 + Tb2O3 → BaZrO3∶Eu3+, Tb3+ SrCO3 → SrO + CO2
SrO + ZrO2 + Eu2O3 + Tb2O3 → SrZrO3∶Eu3+, Tb3+
The synthesized perovskites were subjected to various structural, morphological, topographical, optical and thermal analyses.
Jo
3. Crystallographic analysis
The structural characteristics and crystallographic parameters were studied from the recorded PXRD patterns of synthesized perovskites. Here, 3W PANalytical-XPERT Powder X-ray diffractometer (PXRD) was used for mapping the PXRD patterns as shown in figure 1. It uses the X-ray beam (λ= 0.154 nm) generated by the Cu-anode, to obtain the diffraction patterns obtained for analysis [5].
2
3000
30
20
80
70
60
50
40
3+
SrZrO3:Eu , Tb
3+
(002) 2000
(110) (111)
(420)
(021) (040)
1000
(242) (323) (310)
(240)
3+
BaZrO3:Eu , Tb
3000
3+
(001) (100)
2000
(101) (002) (200) (111)
1000
8000
(102) (112) (220) (310) 3+
CaZrO3:Eu , Tb
(121)
of
INTENSITY ( A.U)
4000
3+
(202) (111)
2000 20
30
(042) (242)
(130) (103) 50
40
60
70
(034)
80
-p
4000
ro
6000
2 Theta (angle)
a (Å)
b (Å)
c (Å)
α,𝞫,γ
Pcmn
7.90
5.60
7.10
Cubic
Pm3m
4.80
5.55
12.5
Orthorhombic
Pcmn
12.8
7.30
10.9
α = 70o 𝞫= 100 o γ = 98o α = 90o 𝞫= 90 o γ = 90o α = 90o 𝞫= 112o γ = 90o
Crystal structure
CaZrO3: Eu3+, Tb3+ (1:1 mol%)
76-2401
Orthorhombic
BaZrO3: Eu3+, Tb3+ (1:1 mol%)
06-0399
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JCPDS card no.
ur na
Phosphors
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Fig 1. PXRD pattern of AZrO3:Eu3+,Tb3+ phosphors
SrZrO3: Eu3+, Tb3+ (1:1 mol%)
44-0161
Space group
Table 1. Crystallographic parameters of AZrO3:Eu3+,Tb3+ phosphors
Jo
The crystallographic studies confirm crystalline structure with homogeneity and phase purity of the synthesized perovskites. No additional peaks of impurity ions were obtained. The table 1 shows crystallographic parameters of AZrO3:Eu3+,Tb3+ and ATiO3:Eu2+,Yb2+ (A=Ca, Ba, Sr) perovskite phosphors [6].
4. FESEM and TEM analyses The topographical and morphological analysis were done here using JEOL-JSM-5200 operating at 20 KV and JEOL JEM 2100 operating at 200 KV respectively.
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(a) (b) Fig 2. FESEM micrographs (a) and (b) of AZrO3:Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
(a) (b) 3+ 3+ Fig 3. TEM micrographs (a) and (b) of AZrO3: Eu ,Tb (A=Ca, Ba, Sr) phosphors
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The FESEM micrographs in Fig. 3 show clusters of particles agglomerated in clumps with shape and sizes. The TEM micrographs in Fig. 4 also well agree with the distinct topography revealed in FESEM analysis [7]. The FESEM micrographs show clusters of particles with irregular shape and variable sizes agglomerated in clusters. The long duration heat treatment sessions at elevated temperatures followed by pro-longed annealing result in agglomeration of the particles [8]. 5. Thermogravimetric Analysis The Thermogravimetric Analysis (TGA) done by using TGA 4000 Pyris 6 TG analyzer in the gaseous atmosphere of nitrogen gas at 20 ml/min. The perovskites per subjected to heat treatment from 30oC to 700oC for study of thermal characteristics. The perovskites exhibit less weight loss% confirming their stability towards thermal invariance. The average weight loss% of 4.51, 3.47 and 11.90% was obtained for CaZrO3:Eu3+,Tb3+, BaZrO3:Eu3+,Tb3+ and SrZrO3:Eu3+,Tb3+ respectively as shown in figure 4 [9].
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Fig 4. TGA curves of AZrO3: Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
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The maximum weight loss% of 11.90% of SrZrO3:Eu3+,Tb3+ indicates that these perovskites were less thermally stable than the other perovskites [10].
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6. Thermoluminescent Study of AZrO3: Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
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The thermoluminescent behavior of synthesized perovskite phosphors pre-exposed to ionizing radiations were studied using TL/OSL Reader 1008 supplied by Nucleonix Systems. The recorded thermograms were deconvoluted and analyzed using Glowfit and TLanal software for estimation of kinetic parameters [11]. 6.1. Thermoluminescent study of UV irradiated phosphors
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The synthesized perovskites were subjected to UVR irradiation of 254 nm for 5 min at room temperature. The TL glow curves were mapped on heating the irradiated sample from room temperature to 500oC with a constant heating rate of 5oC/s [12].
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Fig. 5 TL glow curves of UV irradiated AZrO3: Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
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The synthesized phosphors exhibit both first and second order kinetics, increased quantum yield along with shallow and deep trapping mechanism as shown in figure 5. The CaZrO3:Eu3+,Tb3+ phosphors have the value of average activation energy as 2.27eV with shallow trapping. The BaZrO3:Eu3+,Tb3+ phosphors show the value of average activation energy of 2.16eV. The SrZrO3:Eu3+,Tb3+ phosphors have second order of kinetics with average activation energy of 3eV. This confirms occurrence of deep trapping in these phosphors [13].
6.2. Thermoluminescent study of γ irradiated phosphors
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The synthesized perovskites were irradiated with γ radiation of 5 Gy for 2.2 mins using Theratron 780E, Teletherapy unit with Co60 as the radiation source. The TL glow curves were mapped on heating the irradiated sample from room temperature to 500oC with a constant heating rate of 5oC/s [14]. The source to surface distance is kept 80 cm in a field of 20 𝗑 20 cm2. The TL responses were mapped using TL/OSL Reader 1008 from room temperature to 500 °C at a heating rate of 10 °C/s. The recorded thermograms as shown in figure 6 were deconvoluted and analyzed using Glowfit and TLanal software for estimation of kinetic parameters [15].
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Fig. 6 TL glow curve of γ irradiated AZrO3: Eu3+,Tb3+ (A=Ca, Ba, Sr) phosphors
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The synthesized phosphors exhibit second order kinetics, increased quantum yield along with deep trapping mechanism. The CaZrO3:Eu3+,Tb3+ phosphors have the value of average activation energy as 2.59eV with deep trapping and second order of kinetics [16]. The BaZrO3:Eu3+,Tb3+ phosphors show the value of average activation energy of 2.25eV, second order of kinetics and deep trapping. The SrZrO3:Eu3+,Tb3+ phosphors have second order of kinetics with average activation energy of 3eV. The TL glow curve peaks obtained at higher temperatures indicate the low fading characteristics of these synthesized phosphors [17]. On comparing the TL behavior of both UV irradiated and gamma irradiated samples, it was found that gamma irradiated samples exhibit second order kinetics, deep trapping and low fading characteristics. The glow curve peaks above 500K confirms the low fading behavior of gamma irradiated samples. The TL analysis confirms the competence of synthesized perovskite phosphors for sensing, mapping, radiation detection, exposure assessment and monitoring applications is confirmed through the complete TL behavior analysis [18].
7. Conclusion
The synthesized perovskite phosphors have crystalline nature with appreciable phase purity and homogeneity, which were well confirmed by crystallographic analysis. The distinct morphology and topography of these phosphors were set forth by FESEM and TEM studies. The thermogravimetric or thermal analysis of these phosphors confirms the thermal stability of synthesized perovskites with less weight loss%. The maximum weight loss of 11.90% is obtained for SrZrO3:Eu3+,Tb3+. The thermoluminescent studies of UV irradiated and gamma irradiated samples set forth many interesting traits. These perovskites exhibit both second and first order of kinetics along with deep and shallow
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trapping both. The TL glow curve peaks obtained at higher temperatures indicate the low fading characteristics of these synthesized phosphors and hence confirms their suitability for mapping, sensing and radiation detection pertinences.
Acknowledgement The authors sincerely acknowledge and thanks STIC Kochi University and Department of energy and environment, National Institute of Technology Tiruchirappalli for providing TEM and TGA analysis facility respectively.
Compliance with ethical standards Conflict of interest: We declare that we have no conflict of interest.
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