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Synthesis and characterization of radio and thermoluminescence properties of Sm doped Gd2O3, Gd2O2S and Gd2O2SO4 nanocrystalline phosphors
Journal of Luminescence 220 (2020) 116979
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Synthesis and characterization of radio and thermoluminescence properties of Sm doped Gd2O3, Gd2O2S and Gd2O2SO4 nanocrystalline phosphors Amin Aghay Kharieky , Khadijeh Rezaee Ebrahim Saraee * Faculty of Advance Sciences and Technologies, University of Isfahan, Isfahan, 81746-73441, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords: Gd2O3 Gd2O2S Gd2O2SO4 Luminescence Sm
In this study, nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm phosphors were successfully synthesized through the urea homogeneous precipitation method. Nanocrystalline Gd2O2S:Sm phosphors with two different concentrations of sulfur were prepared. In the first procedure, the weight of sulfur was five times more than Gd2O3 weight (was called sample Gd2O2S:Sm(1)) and in the second procedure, it was equal (was called sample Gd2O2S:Sm(2)). The nanocrystalline powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, radioluminescence and thermoluminescence. The XRD and FT-IR results confirmed that nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders had the cubic, hexagonal and orthorhombic structure in preparation temperatures of 620 � C and 900 � C. The SEM images showed that nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders had a semi-spherical shape with a uniform mean size of about 30 nm in diameter and confirmed the XRD results. The presence of all elements was confirmed in the synthesized samples using EDX spectroscopy. The results showed that the weight percent of sulfur during the preparation of Gd2O2S had an effect on the size, morphology and the luminescence intensity of nanocrystalline Gd2O2S powder. Under X-ray irradiation (40 kV and 40 mA), the emission spectra of nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm phosphors were studied. The results showed the orange-red emission peaks which were observed at 605 nm were the strongest emission peak for all nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders. This peak was corresponded to the 4 G5/2-7H7/2 energy transition of Sm3þ ion. The TL response of Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm after irradiation with different X-ray time exposure exhibited a peak shifting towards the lower temperatures. The glow curve deconvolution method was used to calculate trapping parameters and the obtained results were investigated in detail.
1. Introduction During the recent decade, gadolinium oxide, oxysulfide and oxy sulfate compounds have been widely studied due to their applications in the phosphorescent material design such as electroluminescent displays, X-ray computerized tomography and radiation detection. All these ma terials are well known for their high chemical and thermal stability to withstand a harsh environment that makes them ideal host lattices for RE3þ cations [1–3]. For example, the Gd2O2S has inherent properties such as high X-ray absorption; hard radiation stability and high density (7.44 g/cm3) makes it an effective trap of the incident X-ray photon [1–6]. Because the gadolinium oxide and gadolinium oxysulfate are used as an intermediate phase or a precursor for the synthesis of gado linium oxysulfate and gadolinium oxysulfide, respectively, the synthesis
and characteristics of these precursor materials are important, too [2]. The luminescence properties of each material depend on the nature of activator (rare earth ions) in the host material and also on the position of trap levels within the band gap of the host structure. Much rare earth doped Gd2O2S and Gd2O2SO4, such as Eu, Tb, Pr and Ce were reported by scientists that capable to absorb X-ray radiation and neutron and emit light in a UV–Visible range. Rezaee Ebrahim Saraee et al. reported that the Gd2O2S:Pr and Gd2O2S:Tb, Dy had emission in the 400–650 nm and the prepared scintillator screen was appropriate for X-ray imaging [4,5]. They reported that adding the appropriate amount of Dy to Gd2O2S:Tb can improve emission efficiency. Also, Yasuda et al. synthesized Gd2O2S: Tb scintillator with different grain sizes for neutron imaging [7]. They showed that the grain size of scintillation powder and amount of binder were affective on image resolution. Lian et al. developed a new method
* Corresponding author. E-mail addresses: [email protected], [email protected] (K.R. Ebrahim Saraee). https://doi.org/10.1016/j.jlumin.2019.116979 Received 26 October 2019; Received in revised form 16 December 2019; Accepted 17 December 2019 Available online 24 December 2019 0022-2313/© 2019 Elsevier B.V. All rights reserved.
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
purification. In a typical synthesis, 10 ml of Gd(NO3)3.6H2O (0.5 M) and 10 ml of Sm(NO3)3.6H2O (0.01 M) were mixed and diluted in 400 ml of 95 � C deionised water. Also, 30 g of urea was weighed and dissolved in 120 mL of 95 � C deionised distilled water. The temperature of the mixture was kept more than 95 � C. Next, the urea solution slowly and drop wisely was added to the gadolinium and the samarium nitrate mixture until precipitation was completed. The mixture was kept stir ring for 1.5 h at more than 95 � C temperature. At the end of stirring, the mixture left for 24 h at room temperature. Next, the white precipitation was separated by centrifuge (5000 rpm, 5 min) and washed several times with deionised water and ethanol. The white precursor powder was dried in an oven at 100 � C for 24 h. The white precursor was ob tained at 100 � C was annealed at 620 � C for 1 h to obtain nanocrystalline Gd2O3:Sm powder. Next, nanocrystalline Gd2O2S:Sm powder was ob tained by annealing Gd2O3:Sm powder with two different concentra tions of sulfur powder. To prepare Gd2O2S:Sm(1) powders, the weight of sulfur powder was 5 times more than the weight of gadolinium oxide and for synthesizing Gd2O2S:Sm(2) powders it was equal. The prepared white powder of the previous step (gadolinium oxide prepared at 620 � C) was mixed with sulfur and heated in a sealed quartz container (about 500 ml) at 900 � C for 1 h purged and filled with an argon atmosphere. The cooling process was done at room temperature. The Gd2O2S:Sm(1) powder which was prepared with a high concentration of sulfur had a gray colour. The Gd2O2SO4:Sm powder was obtained by heating the mixture of the high concentration of sulfur powder and white powder of gadolinium oxide (prepared at 620 � C) in a ceramic crucible inside of the closed steel tube (1.5 m long, 3 inch diameter) and atmospheric condition. The screens from nanocrystalline Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S: Sm(2) and Gd2O2SO4:Sm powders were prepared for using them in X-ray induced emission by coating uniformly on glass substrates. The size of the glass substrates was 1.8 � 1.8 cm2 and 0.13 cm thickness. The coating solution was prepared by nano phosphor powders, polyvinyl alcohol (PVA) and deionised water. First, 5.5% (weight percent) PVA was dissolved into deionised water at a temperature of more than 90 � C. Then, 120 mg of nano phosphor powders were added to the above cool solution and stirred vigorously. Next, all mixtures were poured into a vertical cylindrical tube that the glass substrate was at the bottom. When the sedimentation process was completed, the coated substrate was removed from vertical the cylindrical tube and was dried at room tem perature. The prepared scintillator screen is shown in Fig. 1. The screen coating thickness (mg/cm2) was calculated by equation (1) [4]:
Fig. 1. Scintillation screen used in X-ray luminescence examination.
to prepare red emitter of Gd2O2SO4:Eu because they found out that Gd2O2SO4:Eu has good thermal stability and also a good red light emission when excited under X-ray or ultraviolet light [8,9]. Also, there is a lot of researches that shows scientists are developing Gd2O2S:Tb, Gd2O2S:Eu and Gd2O2S:Pr with other co-doped rare earth to improve luminescence properties and better application. Mochiki et al. used the Gd2O2S:Tb and Gd2O2S:Eu scintillators and introduced a new scintil lator base on different light emissions that were a characteristic property of Tb and Eu. They used two colour scintillator for discrimination of gamma and neutron in the mixed radiation field [5,7–10]. In 2006 and 2017, Dosev et al. and Boopathi et al. studied Gd2O3 doped Sm in the form of nanopowders and nanorods, respectively [3,11]. They used co-precipitation technique and spray pyrolysis method to prepare the Gd2O3:Sm. They prepared nanopowders (5 at.% Sm) and nanorods (20 at.% Sm) of Gd2O3:Sm with 50 nm dimension and 110–420 nm length (50–90 nm diameters), respectively. The structural properties of Gd2O3: Sm were investigated in detail and photoluminescence properties were reported. They reported that Gd2O3:Sm had a good photoluminescence spectrum in the 300–800 nm and band gap of more than 4eV. Fewer reports can be found about Gd2O2S and Gd2O2SO4 which were doped by Sm and most of the papers reported on luminescence properties of micro crystalline and nano crystalline phosphors except the Gd2O2S:Sm and Gd2O2SO4:Sm [2–9]. Increasing the quality of detection of high and low energy radiation and having display devices with better resolution, phosphors with higher scintillation properties such as higher lumines cence efficiency, modified morphology, particle size, and distribution are needed [5]. In this research, the radio- and thermo-luminescence properties of the Sm doped gadolinium oxide, oxysulfide and oxy sulfate compounds that well distributed in morphology were studied in detail. The doping percentage of samarium was maintained to 2 mol% because the goal of this study was an investigation of the effect of different hosts of gadolinium oxide, oxysulfide and oxysulfate on the luminescence properties. Here, the luminescence properties of prepared phosphors with uniform spherical morphology and crystallite size less than 30 nm were studied on the qualitative discussion.
E ¼ ðm1 m2 Þ=S
(1)
where E is the screen coating density and S is the substrate area (in cm2), m1 and m2 are the masses of the screen after and before sedimentation (in mg), respectively. 2.2. Characterization The nanocrystalline powders were characterized by X-ray powder diffraction (XRPD) using a Bruker D8 Advance X-ray powder diffrac tometer (Cu-Kα, λ ¼ 1.5406 Å with Ni filter) to determine the crystal phase and size. To determine the shape and size of the nanocrystalline powder, scanning electron microscopy (SEM) images were obtained with a VEGA, TESCAN SEM (TESCAN, Brno, Czech Republic) which equipped with an XMU unit for energy dispersive X-ray spectroscopy to confirm the presence of impurities in the samples. The Fourier transform infrared (FT-IR) and ultraviolet–visible (UV–Vis) absorption spectra were recorded with a JASCO spectrometer, FTIR-6000 and V-670 models, respectively. The radioluminescence (RL) spectra of samples under X-ray excitation were measured using the high sensitivity spec trometer (Aurora 4000) coupled with an ASENWARE X-ray generator (XJ10-60 N model, Cu anode). To avoid direct X-ray exposure of CCD detectors, the scintillation light was measured by feeding into the
2. Experimental 2.1. Method of preparation of nanocrystalline powders Nanocrystalline Gd2O3:Sm (2 mol%), Gd2O2S:Sm (2 mol%) and Gd2O2SO4:Sm (2 mol%) powders were prepared by the urea homoge neous precipitation method. The raw materials of Gd(NO3)3.6H2O (99.9%, Sigma–Aldrich), Sm(NO3)3.6H2O (99.9%, Exir), urea (99.5%, Merck), and sulfur (99%, Merck) were purchased and used without 2
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
Fig. 2. (a) The Gd2O3:Sm, (b) and (c) Gd2O2S:Sm (high and low sulfur concentration, respectively) and (d) Gd2O2SO4:Sm nanocrystalline X-ray diffraction patterns.
Fig. 3. Determination of the lattice parameters for (a) the Gd2O3:Sm and (b) Gd2O2S:Sm (high sulfur concentration) nanocrystalline powders.
spectrometer through a 2 m optical fibre. All measurements were per formed at room temperature. The RL emission spectra were corrected using a detector correction curve. Also, all nanocrystalline powders were exposed to different times 1, 5, 7 and 12 min of X-rays (V ¼ 40 kV and I ¼ 40 mA) and then the glow curves of them were recorded by an IAP7103 TLD Reader (Institute of Applied Physics, Tehran, Iran).
3. Result and discussion 3.1. XRD study Fig. 2(a)–(d) show the XRD patterns obtained for Gd2O3:Sm, Gd2O2S: Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline powders, respectively. In order to compare the prepared nanocrystalline powders with their pure structure; the reference patterns are shown in figures 3
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Journal of Luminescence 220 (2020) 116979
agreement with the standard data in JCPDS card No. 29–613 and fitted with the orthorhombic structure. No impurity phases were present in the XRD patterns, thereby demonstrating that all of the nanocrystalline powders were prepared with high purity. The strongest diffraction peaks in diffraction patterns were used to calculate the crystallite size using the Debye-Scherrer equation, equation (2):
Table 1 Crystallite size and lattice parameters of the nanocrystalline powders. Sample
Gd2O3 Gd2O2S (high sulfur concentration) Gd2O2S (low sulfur concentration) Gd2O2SO4
DebyeSherer
Lattice parameters
D (nm)
JCPDS (Å)
Calculated(Å)
11 21
a ¼ 10.813 a ¼ 3.852 c ¼ 6.667 a ¼ 3.852 c ¼ 6.667 a ¼ 4.062 b ¼ 4.188 c ¼ 12.960
a ¼ 10.753 a ¼ 3.830 c ¼ 6.501 a ¼ 3.831 c ¼ 6.642 a(103) ¼ 4.0138 b(011) ¼ 4.1419 c(002) ¼ 12.808
19 17
D ¼ kλ=βcos θ
(2)
where D is the average grain size of nanocrystalline powder, k (0.9) is the shape factor and constant value, λ, is the X-ray wavelength (1.5406 Å),βis the full width at half maximum (FWHM) and θis the diffraction angle of an observed peak in a diffraction pattern. The average crys tallite size was obtained approximately 11, 21, 19 and 17 nm for Gd2O3: Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline powders, respectively. Also, the results showed the procedure of prep aration of Gd2O2S was affected on the crystallite size as with decreasing concentration of sulfur a decrease of crystallite size of nanocrystalline Gd2O2S powder was observed. The Nelson–Riley method can be used to interpret X-ray diffraction spectra. In the cubic and hexagonal struc tures, the lattice constants a and c can be calculated by Nelson–Riley method using equation (3): � �� � � 1 cos2 θ cos2 θ f ðθ ¼ þ (3) 2 sin θ θ
(standard data available, JCPDS card No. 12–797, 26–1422 and 29–613). All diffraction patterns of nanocrystalline powders matched well with the standard data in the JCPDS card. The position and in tensity of peaks in the XRD pattern of Gd2O3:Sm was an agreement with standard data of JCPDS card No. 12–797 and peaks fitted with a Bodycentred cubic and space group of Ia3. The XRD patterns of Gd2O2S:Sm (1) and Gd2O2S:Sm(2) were an agreement with the standard data in JCPDS card No. 26–1422 and also fitted with the hexagonal structure (space group P3-m1). The XRD pattern of Gd2O2SO4:Sm was an
Fig. 4. The FTIR spectra of (a) the Gd2O3:Sm, (b) Gd2O2S:Sm and (d) Gd2O2SO4:Sm nanocrystalline powders. 4
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Journal of Luminescence 220 (2020) 116979
Fig. 5. SEM images of (a) the Gd2O3:Sm, (b) and (c) Gd2O2S:Sm (high and low sulfur concentration, respectively) and (d) Gd2O2SO4:Sm nanocrystalline powders.
Fig. 3 (a) and (b) show calculated lattice constants for nanocrystal line Gd2O3:Sm and Gd2O2S:Sm(1) powders. The lattice constant is determined from the intercept of a linear plot of the Nelson-Riley equation versus the lattice parameter. Also, the lattice constants for Gd2O2SO4:Sm nanocrystalline powder was calculated for the deter mined index Miller plane ((103), (011), (002)). The results of lattice parameters and crystallite size of all nanocrystalline powders were re ported in Table 1. All nanocrystalline powders had crystallite sizes of less than 30 nm. The nanocrystalline Gd2O2S:Sm and Gd2O2SO4:Sm powders (prepared at 900 � C) had a bigger crystallite size than their precursor (Gd2O3:Sm prepared at 620 � C) that showed probably changing the crystal structure or annealing temperature were effective on crystallite size. The Gd2O3:Sm nanocrystalline powder and the Gd2O2S:Sm(1) nanocrystalline powder had the smallest and the biggest crystallite size, respectively.
intensity exist in the Gd2O2S and Gd2O2SO4 spectra. The band absorp tion with more intensity around 550-1500 cm 1 in the Gd2O2SO4 spectrum assigned to SO4 2 that confirms gadolinium oxysulfate was formed. The absorption band about 350–550 cm 1 assigned to the vi bration of Gd–O and Gd–S that confirms Gd2O3, Gd2O2S and Gd2O2SO4 formation [2,4]. 3.3. SEM and EDX studies The surface morphology and particle size of nanocrystalline Gd2O3: Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm powders are shown in Fig. 5(a)–(d), respectively. The SEM images of the nano crystalline powders showed the semi-spherical shapes and tended to agglomeration. The nanocrystalline Gd2O2S:Sm and Gd2O2SO4:Sm powders inherited the morphology of Gd2O3:Sm (precursor prepared at 620 � C) and the particle size was almost uniform. The size of the par ticles was varied from 20 nm to 40 nm. By increasing sulfur concen tration to the precursor of Gd2O3 during the Gd2O2S preparation an increase in the agglomeration tendency was observed (compare Fig. 5(b) and (c)). Increasing the annealing temperature to 900 � C was caused that nano particles of Gd2O2SO4:Sm were a little bigger than nano particles of Gd2O3:Sm and agglomeration tendency was decreased, too. EDX anal ysis of nanocrystalline powders confirmed the elemental composition of the powders (Fig. 6 (a)–(c)). The presence of constituent elements of nanocrystalline powders that consist of gadolinium (Gd), oxygen (O),
3.2. FTIR study Fig. 4 (a)–(c) show the FT-IR spectra of Sm doped Gd2O3, Gd2O2S(1) and Gd2O2SO4, respectively. The FT-IR spectra of Sm doped Gd2O2S(1) and Gd2O2S(2) were the same. In all Fig. 4 (a)–(c), the broad absorption band around 2800-3800 cm 1 can be assigned to O–H stretching vi bration of absorbed water from the air. The band around 750-2000 cm 1 in the Gd2O3 spectrum assigned to C–O and CO3 2 vibration and disap pears in high annealing temperature. Also, these bands with less 5
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
Fig. 6. The EDX spectrum of (a) the Gd2O3:Sm, (b) Gd2O2S:Sm (high concentration) and (c) Gd2O2SO4:Sm nanocrystalline powders.
Fig. 7. UV–Visible absorbance spectra of the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm.
sulfur (S) and samarium (Sm) elements was investigated for each syn thesized nanocrystalline powders. Also, it was observed carbon peaks with low intensity. It is disappearing at higher annealing temperature.
3.4. UV–visible study Fig. 7 illustrates the UV–Visible absorption of nanocrystalline Gd2O3: 6
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Journal of Luminescence 220 (2020) 116979
Fig. 8. The radioluminescence spectrum of the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm screens.
related to the host crystal, the energy transfer of an electron from 2p or 3p orbital of O2 and S2 to the 5d orbital of Gd3þ ion [12]. This band for nanocrystalline Gd2O2S:Sm powders was broader in compared to the absorption band for nanocrystalline Gd2O3:Sm and Gd2O2SO4:Sm powders. It seems that the maximum absorption intensity for nano crystalline Gd2O3:Sm and Gd2O2SO4:Sm powders went to a shorter wavelength. The data of optical absorption spectra and Tauc equation were used to obtain the band gap values. The band gap of nanocrystal line powders was obtained approximately 5.02, 4.12 and 5.08 eV for Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm, respectively. The strong ab sorption band shows that the band gap of all nano crystalline powder is approximately more than 4 eV and the band gap of Gd2O3:Sm and Gd2O2SO4:Sm are a little more than Gd2O2S:Sm band gap. Also, there was a weak absorption band with low intensity in the UV–Visible ab sorption spectrum only for nanocrystalline Gd2O3:Sm and Gd2O2SO4:Sm powders. It is maybe attributed to have a wider band gap of these phosphors compared to the crystalline Gd2O2S:Sm powders. The weak absorption band around 265 nm and 326 nm have corresponded to the 8 S7/2-6I7/2 and 8S7/2-6P7/2 transitions of Gd3þ ion, respectively [13]. Also, there was a peak with low intensity in the range of 350–700 nm for all nanocrystalline Gd2O3:Sm, Gd2O2S:Sm, and Gd2O2SO4:Sm powders. It may be attributed to the internal f-f absorption transition of Sm3þ ion (maximum intensity related to 6H5/2-6P3/2 energy transition) [13] or because trivalent rare earth ions demonstrate a very narrow band due to the shielding of 4f-orbital by external 5s- and 5p-shells, with most likely, the nature of this band is associated with intrinsic defects of hosts, like oxygen vacancies, for example.
Fig. 9. CIE chromaticity coordinate of the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline phosphors.
3.5. Radio-luminescence and X-ray imaging studies The radioluminescence (RL) examination was done because an X-ray photon can penetrate entire samples and create enormous electrons and holes by exciting electrons from a valence band to conduction band that recombines consequently and allows detecting all possible transitions in the emission spectrum. The X-ray induced luminescence spectra for nanocrystalline Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm powders are shown in Fig. 8. The measurement was done for all prepared screens of nanophosphors in the same condition. The screen thickness density was about 20 mg/cm2. The X-ray of 40 kV and 40 mA was used and the RL spectrum was examined at room tempera ture. All nanocrystalline powders had four emission peaks at 564, 605, 648 and 704 nm which were assigned to 4G5/2-6H5/2, 4G5/2-6H7/2, 4G5/ 6 4 6 3þ ion, respectively 2- H9/2 and G5/2- H11/2 energy transitions of Sm
Fig. 10. The X-ray radiography images obtained for Gd2O2SO4:Sm screen at different irradiation conditions.
Sm, Gd2O2S:Sm, and Gd2O2SO4:Sm powders which showed all nano crystalline powders consisted of a strong absorption band around 220–237 nm, 220–300 nm and 220–247 nm, respectively. The absorp tion band around 220–237 nm, 220–300 nm and 220–247 nm was 7
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Journal of Luminescence 220 (2020) 116979
Fig. 11. Glow curves of (a) all nanocrystalline powders (7min, X-ray irradiation) and, (b) the Gd2O3:Sm, (c) and (d) Gd2O2S (high and low sulfur concentration, respectively) and (e) Gd2O2SO4 nanocrystalline powders irradiated with different times of X-rays.
[14]. The RL emission spectra showed the strongest peak centred at 605 nm and it was the predominant emission peak for all samples. The emission intensity of the energy transition of 4G5/2-6H11/2 was the least for nanocrystalline Gd2O3:Sm powder. It showed that the symmetric cubic structure and the low lattice crystal field of the Gd2O3 were affected energy level separation and then the low intensity of the Sm3þ
emission was caused. The emission spectrum for nanocrystalline Gd2O2SO4:Sm powder showed narrow and sharp peaks and overall the Gd2O2S:Sm and Gd2O2SO4:Sm spectra were a little shifted to lower wavelength in comparison to nanocrystalline Gd2O3:Sm powder. It is maybe attributed to increasing in lattice crystal field and energy level separation due to 8
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
Fig. 12. Glow curves of (a) the Gd2O3:Sm, (b) and (c) Gd2O2S:Sm (high and low sulfur concentration, respectively) and (d) Gd2O2SO4:Sm nanocrystalline powders were recorded at different heating rates (3, 5, 7K/s).
change the symmetry of the structure of Gd2O2S:Sm and Gd2O2SO4:Sm nano crystals and Sm3þ ion position in the crystal lattice. The maximum and minimum emission intensities were related to nanocrystalline powders of Gd2O2SO4:Sm and Gd2O3:Sm, respectively. Also, the emis sion intensity for nanocrystalline Gd2O2S:Sm(1) was less than Gd2O2S: Sm(2). Probably, the excess sulfur was caused the Gd2O2S:Sm(1) powder turns gray which the gray colour compared to the white colour of Gd2O2S:Sm(2) powder had more self-absorption and was caused a decrease in emission intensity of gray Gd2O2S:Sm(1) powder. Moreover, the RL spectra of Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nano crystalline powders showed a good emission in the range of 400–800 nm that compatible with the most of commercial PMTs and photodiode detectors. CIE chromaticity coordinate of the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline phosphors are shown in Fig. 9. As the RL result showed, different hosts and different concentrations of sulfur were effective on the Sm emission spectrum corresponded to different CIE coordinates in the orange-red emission region. Fig. 10 shows the X-ray radiography images obtained from the screen of Gd2O2SO4:Sm coupled with a radiographic film. Measurements were carried out for different voltage (60 kVp and 64 kVp), same irradiation times and constant current (0.064s, 8 mA, planmeca intra, dental x-ray machine). The optical intensity of dark areas affected by screen scintil lation for 60 kV, 8 mA (0.064s) and 64 kV, 8 mA were 2.1 and 2.77, respectively. Increasing voltage and X-ray energy enhanced the screen
light output and image resolution. 3.6. TL study In order to characterise the trap levels that exist in the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline phosphors, all nano crystals were irradiated with different times (1, 5, 7 and 12 min) of Xrays and the TL glow curves of the irradiated phosphors were recorded at different heating rates in the range of 323–673 K. The TL glow curves obtained for the Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline powders were recorded after 7 min irra diation (40 kV, 40 mA) of X-ray exposure (Fig. 11 (a)). The irradiated nanocrystalline powders were read at a heating rate of 3K/s for 150 s and at a maximum temperature of 673 K. Preheating was applied at 323K. Fig. 11(a) shows that the TL glow curve was obtained for nano crystalline Gd2O3:Sm powder had four peaks near 403, 447, 496 and 619 K. The glow curve for nanocrystalline Gd2O2S:Sm powder was contained two intensive peaks at 407 K and 643 K. Also, the TL glow curve for nanocrystalline Gd2O2SO4:Sm powders was contained two intensive peaks at 413 K and 506 K. The area under the glow curve was obtained 732597, 277560, 1.43 � 106 and 9.21 � 107 counts for Gd2O3: Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline powders in the 323–650 K, respectively. Fig. 11 (b)–(e) show the dose dependence of the TL glow curves for all nanocrystalline phosphorous which were irradiated with different 9
Journal of Luminescence 220 (2020) 116979
A.A. Kharieky and K.R. Ebrahim Saraee
Fig. 13. Comparison between the experimental and the fitted TL glow for the 5 min X-ray irradiation (3K/s) (a) the Gd2O3:Sm, (b) and (c) Gd2O2S:Sm (high and low sulfur concentration, respectively) and (d) Gd2O2SO4:Sm nanocrystalline powders. Table 2 Kinetic parameters of the deconvoluted TL glow curves of the Sm doped (a) Gd2O3, (b) and (c) Gd2O2S (high and low sulfur concentration, respectively) and (d) Gd2O2SO4 nanocrystalline samples. peak
Tm(K)
T1(K)
T2(K)
μg
Order of kinetic
Eτ (eV)
Eδ (eV)
Eω (eV)
Eave (eV)
a a
612.40
560.69
664.12
0.50
1.92
0.89
0.97
0.94
0.93
b
502.40
460.59
544.22
0.50
1.92
0.74
0.81
0.78
0.78
c
446.60
423.59
469.62
0.50
1.92
1.16
1.16
1.17
1.16
d
404.00
382.32
425.69
0.50
1.92
1.00
1.01
1.01
1.01
b a
646.40
587.36
705.45
0.50
1.92
0.85
0.94
0.90
0.90
559.93
525.65
594.22
0.50
1.92
1.19
1.22
1.21
1.21
c
489.78
456.41
523.17
0.50
1.92
0.92
0.96
0.94
0.94
d
437.19
414.46
459.93
0.50
1.92
1.12
1.13
1.12
1.12
e
404.31
370.10
438.52
0.50
1.92
0.58
0.64
0.62
0.63
)
1.42 � 106
2.35 � 106
9.46 � 1011 2.77 � 1011
2.80 � 105
3.81 � 109 2.48 � 108
7.16 � 1011 2.06 � 106
FOM ¼ 0.0223 675.63
628.29
722.97
0.50
1.92
1.22
1.29
1.26
1.26
b
588.27
543.17
633.39
0.50
1.92
0.96
1.02
0.99
0.99
c
480.56
427.22
533.92
0.50
1.92
0.49
0.58
0.53
0.53
d
406.65
374.87
438.45
0.50
1.92
0.64
0.69
0.67
0.67
d a
1
FOM ¼ 0.0184
b
c a
S (s
8.89 � 107
1.21 � 107 1.21 � 104 1.13 � 107
FOM ¼ 0.0208 624.49
569.55
679.44
0.50
1.92
0.86
0.95
0.91
0.90
b
503.50
463.26
543.75
0.50
1.92
0.78
0.84
0.81
0.81
c
413.60
384.23
442.98
0.50
1.92
0.74
0.78
0.76
0.76
FOM ¼ 0.0236
10
6.04 � 105
5.58 � 106 1.04 � 108
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
times of X-rays (1, 5, 7 and 12 min). Almost the shape of the TL glow peaks was not changed significantly with increasing time of X-ray irra diation. By increasing the time of irradiation and X-ray doses, the in tensity of the TL glow peaks was increased and the position of peaks was shifted toward lower temperatures (more than 8 K for all glow curves of nano phosphors). By increasing the irradiation time and X-ray doses, the number of trapping centres and the creation of electron-hole pairs was increased and the intensity of peaks in each glow curve was increased. The TL glow peaks were obeyed second-order kinetics because with increasing the X-ray doses, the peaks were shifted to a lower tempera ture and the shape of the glow curve was not changed, [15]. Also, the TL glow curves of all Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline phosphors were recorded at different heating rates (3, 5, 7 K/s) for 5 min irradiation of X-rays (Fig. 12). With increasing the heating rate, a shift in a peak position, more than 6 K, to higher temperature was recorded and an increase in TL intensity was observed. These results also indicated that the second-order kinetics is a good method to analyze the glow curves [15]. The trap levels of the Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline phosphors which are in the band gap were characterized by order of kinetics, trap depth or activation energy and frequency factor. In the present research, trapping parameters were determined by the computerized glow curve deconvolution (CGCD) method base on the shape of the glow curve of samples and the order of kinetics for the TL glow peaks for all samples. For this purpose, the Chen formula was used, Eα ¼ cα (kT2m/α) – bα (2kTm), where k is Boltzmann constant (8.6 � 10 5 eVK 1), α ¼ τ, δ, ω and cτ ¼ 1.51 þ 3.0(μg-0.42), cδ ¼ 0.976 þ 7.3(μg-0.42), cω ¼ 2.52 þ 10.2(μg-0.42) and bτ ¼ 1.58 þ 4.2 (μg-0.42), bδ ¼ 0, bω ¼ 1) [16,17]. In the Chen method, the shape pa rameters were used to determine the order of kinetics. Total half-intensity width (T2-T1) and high temperature half width (T2-Tm) were used for interpretation of the order of kinetics which Tm is the peak of temperature at maximum intensity and T1 and T2 are the tempera tures on either side of Tm. Chen used a symmetry factor (μg¼(T2-Tm)/(T2-T1)) to identify the first- and second-order of the ki netics of TL glow curves. The symmetry factor lies between 0.37 and 0.56 which is close to 0.42 for first order kinetics and 0.52 for second order kinetics [18]. All TL glow curves of the Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline samples were decon voluted using the origin software program in order to obtain isolated peaks (Fig. 13). The calculated FOM values were less than 2.5%, it means fitted peaks were matched well and good agreement with experimental data. Then, the trapping parameters of each sample were determined for each deconvoluted peak. The order of kinetics for each deconvoluted peak was close to second order kinetics (μg ¼ 0.5). All detail about trapping parameters of the deconvoluted peaks for the Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nano crystalline phosphors were summarized in Table 2 (a)–(d). All the deconvoluted peaks in all glow curves were found to obey second-order kinetics that indicating the retrapping phenomena of charge carriers were occurring.
temperatures with increasing doses and confirmed second order kinetics behaviour. Trapping parameters were investigated and calculated from TL data using glow curve analysis and computerized glow curve deconvolution (CGCD) method. The glow curve examination showed that the shape of the glow curve of Gd2O2S:Sm and Gd2O2SO4:Sm nano phosphors were changed and completely different than their precursors (Gd2O3:Sm). The calculated activation energy of Gd2O2S:Sm and Gd2O2SO4:Sm nano phosphors showed that these nano phosphors had deeper trap centres in comparison to Gd2O3:Sm nano phosphor. Also, The X-ray induced luminescence results of Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline powders showed a good emission in the range of 400–800 nm that compatible with the most of commercial PMTs and photodiode detectors. The X-ray induced luminescence results showed that the Gd2O2SO4:Sm nanocrystalline powder for the same weight of host material and the same doping level of Sm had the most emission intensity. The X-ray imaging results showed that the screen of Gd2O2SO4:Sm nano phosphor is suggested for the scintillation applica tion and can be an appropriate choice for the X-ray imaging applica tions. Also, the Gd2O2SO4:Sm nanocrystalline powder could be used in integration mode as a scintillator in medical and industrial X-ray digital imaging inspection systems with more scintillation efficiency in com parison to Gd2O3:Sm, Gd2O2S:Sm nanocrystalline powders at the same application. CRediT authorship contribution statement Amin Aghay Kharieky: Investigation, Methodology, Project administration, Resources, Software, Writing - original draft, Validation, Visualization. Khadijeh Rezaee Ebrahim Saraee: Conceptualization, Data curation, Formal analysis, Funding acquisition, Supervision, Vali dation, Visualization, Writing - review & editing. References [1] X. Yan, G.R. Fern, R. Withnall, J. Silver, Effects of the host lattice and doping concentration on the colour of Tb3þ cation emission in Y2O2S:Tb3þ and Gd2O2S:Tb3 þ nanometer sized phosphor particles, Nanoscale (2013), https://doi.org/10.1039/ c3nr01034a. [2] S.A. Osseni, Yu G. Denisenko, J.K. Fatombi, E.I. Salnikova, O.V. Andreev, Synthesis and characterization of Ln2O2SO4 (Ln ¼ Gd, Ho, Dy and Lu) nanoparticles obtained by coprecipitation method and study of their reduction reaction under H2 flow, J. Nanostruct. Chem. (2017), https://doi.org/10.1007/s40097-017-0243-4. [3] G. Boopathi, S. Gokul Raj, G. Ramesh Kumar, R. Mohan, S. Mohan, Synthesis of samarium doped gadolinium oxide nanorods, its spectroscopic and physical properties, Indian J. Phys. (2018), https://doi.org/10.1007/s12648-017-1158-0. [4] A. Bagheri, Kh Rezaee Ebrahim Saraee, H.R. Shakur, H. Zamani Zeinali, Synthesis and characterization of physical properties of Gd2O2S:Pr3þ semi-nanoflower phosphor, Appl. Phys. A (2016), https://doi.org/10.1007/s00339-016-0058-z. [5] Kh Rezaee Ebrahim Saraee, M. Darvish Zadeh, M. Mostajaboddavati, A. Aghay Kharieky, Changes of Tb emission by non-radiative energy transfer from Dy in Gd2O2S:Tb Phosphor, J. Electron. Mater. (2016), https://doi.org/10.1007/s11664016-4639-6. [6] Z. Luo, J.G. Moch, S.S. Johnson, C.C. Chen, A review on X-ray detection using nanomaterials, Curr. Nanosci. (2017), https://doi.org/10.2174/ 1573413713666170329164615. [7] R. Yasuda, M. Katagiri, M. Matsubayashi, Influence of powder particle size and scintillator layer thickness on the performance of Gd2O2S:Tb scintillators for neutron imaging, Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrom. Detect. Assoc. Equip. (2012), https://doi.org/10.1016/j.nima.2012.03.035. [8] S. Blahuta, B. Viana, A. Bessiere, E. Mattmann, B. La Course, Luminescence quenching processes in Gd2O2S:Pr3þ,Ce3þ scintillating ceramics, Opt. Mater. (2011), https://doi.org/10.1016/j.optmat.2011.02.040. [9] J. Lian, F. Liu, X. Wang, X. Sun, Hydrothermal synthesis and photoluminescence properties of Gd2O2SO4:Eu3þ spherical phosphor, Powder Technol. (2014), https:// doi.org/10.1016/j.powtec.2013.11.021. [10] K. Mochiki, Y. Murata, K. Nittoh, Neutron gamma ray radiography using a twocolor luminescent scintillator, Appl. Radiat. Isot. (2004), https://doi.org/10.1016/ j.apradiso.2004.03.074. [11] D. Dosev, I.M. Kennedy, M. Godlewski, I. Gryczynski, K. Tomsia, E.M. Goldys, Fluorescence upconversion in Sm-doped Gd2O3, Appl. Phys. Lett. (2006), https:// doi.org/10.1063/1.2161400. [12] R. Manigandan, K. Giribabu, R. Suresh, S. Munusamy, S. Praveen kumar, S. Muthamizh, T. Dhanasekaran, A. Padmanaban, V. Narayanan, Synthesis, growth and photoluminescence behaviour of Gd2O3SO4:Eu3þ nanophosphors: the effect of temperature on the structural, morphological and optical properties, RSC Adv. (2015), https://doi.org/10.1039/C4RA13897J.
4. Conclusion The Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm semi-spherical nano crystalline phosphors were successfully synthesized through the modi fied method by urea homogeneous precipitation method. The characterized nanocrystalline powders results confirmed that all the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline powders synthesized had cubic, hexagonal and orthorhombic structure and had uniform mean size of about 30 nm diameters. The strongest orange-red emission peak by X-ray excitation was observed located at 605 nm for the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nano particles which correspond to the 4G5/2-6H7/2 transition of the Sm3þ ions. The thermo luminescence (TL) studies on Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nano particles showed a shifting of the peaks towards lower 11
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
[13] N. Wantana, S. Kaewjaeng, S. Kothan, H.J. Kim, J. Kaewkhao, Energy transfer from Gd3þ to Sm3þ and luminescence characteristics of CaO– Gd2O3– SiO2– B2O3 scintillating glasses, J. Lumin. (2017), https://doi.org/10.1016/j. jlumin.2016.09.050. [14] A. Herrera, R.G. Fernandes, A.S.S. de Camargo, A.C. Hernandes, S. Buchner, C. Jacinto, N.M. Balzaretti, Visible–NIR emission and structural properties of Sm3þ doped heavy-metal oxide glass with composition B2O3–PbO–Bi2O3–GeO2, J. Lumin. (2016), https://doi.org/10.1016/j.jlumin.2015.10.065. [15] S. Som, A. Choubey, S.K. Sharma, Spectral and trapping parameters of Eu3þ in Gd2O2S nanophosphor, Opt. Mater. (2015), https://doi.org/10.1080/ 17458080.2013.837972.
[16] V. Kumar, H.C. Swart, O.M. Ntwaeaborwa, R. Kumar, S.P. Lochab, Varun Mishra, Nafa Singh, Thermoluminescence response of CaS:Bi3þ nanophosphor exposed to 200 MeV Agþ15 ion beam, Opt. Mater. (2009), https://doi.org/10.1016/j. optmat.2009.06.018. [17] Kh R. Ebrahim Saraee, A.A. Kharieky, Maryam Erfani, Synthesis, characterization and TL properties of SrSO4:Dy,Tb nanocrystalline phosphor, J. Rare Earths (2014), https://doi.org/10.1016/S1002-0721(14)60174-5. [18] P.D. Sahare, R. Ranjan, N. Salah, S.P. Lochab, K3Na(SO4)2:Eu nanoparticles for high dose of ionizing radiation, J. Phys. D Appl. Phys. (2007), https://doi.org/ 10.1088/0022-3727/40/3/011.
12
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: http://www.elsevier.com/locate/jlumin
Synthesis and characterization of radio and thermoluminescence properties of Sm doped Gd2O3, Gd2O2S and Gd2O2SO4 nanocrystalline phosphors Amin Aghay Kharieky , Khadijeh Rezaee Ebrahim Saraee * Faculty of Advance Sciences and Technologies, University of Isfahan, Isfahan, 81746-73441, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords: Gd2O3 Gd2O2S Gd2O2SO4 Luminescence Sm
In this study, nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm phosphors were successfully synthesized through the urea homogeneous precipitation method. Nanocrystalline Gd2O2S:Sm phosphors with two different concentrations of sulfur were prepared. In the first procedure, the weight of sulfur was five times more than Gd2O3 weight (was called sample Gd2O2S:Sm(1)) and in the second procedure, it was equal (was called sample Gd2O2S:Sm(2)). The nanocrystalline powders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, radioluminescence and thermoluminescence. The XRD and FT-IR results confirmed that nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders had the cubic, hexagonal and orthorhombic structure in preparation temperatures of 620 � C and 900 � C. The SEM images showed that nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders had a semi-spherical shape with a uniform mean size of about 30 nm in diameter and confirmed the XRD results. The presence of all elements was confirmed in the synthesized samples using EDX spectroscopy. The results showed that the weight percent of sulfur during the preparation of Gd2O2S had an effect on the size, morphology and the luminescence intensity of nanocrystalline Gd2O2S powder. Under X-ray irradiation (40 kV and 40 mA), the emission spectra of nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm phosphors were studied. The results showed the orange-red emission peaks which were observed at 605 nm were the strongest emission peak for all nanocrystalline Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm powders. This peak was corresponded to the 4 G5/2-7H7/2 energy transition of Sm3þ ion. The TL response of Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm after irradiation with different X-ray time exposure exhibited a peak shifting towards the lower temperatures. The glow curve deconvolution method was used to calculate trapping parameters and the obtained results were investigated in detail.
1. Introduction During the recent decade, gadolinium oxide, oxysulfide and oxy sulfate compounds have been widely studied due to their applications in the phosphorescent material design such as electroluminescent displays, X-ray computerized tomography and radiation detection. All these ma terials are well known for their high chemical and thermal stability to withstand a harsh environment that makes them ideal host lattices for RE3þ cations [1–3]. For example, the Gd2O2S has inherent properties such as high X-ray absorption; hard radiation stability and high density (7.44 g/cm3) makes it an effective trap of the incident X-ray photon [1–6]. Because the gadolinium oxide and gadolinium oxysulfate are used as an intermediate phase or a precursor for the synthesis of gado linium oxysulfate and gadolinium oxysulfide, respectively, the synthesis
and characteristics of these precursor materials are important, too [2]. The luminescence properties of each material depend on the nature of activator (rare earth ions) in the host material and also on the position of trap levels within the band gap of the host structure. Much rare earth doped Gd2O2S and Gd2O2SO4, such as Eu, Tb, Pr and Ce were reported by scientists that capable to absorb X-ray radiation and neutron and emit light in a UV–Visible range. Rezaee Ebrahim Saraee et al. reported that the Gd2O2S:Pr and Gd2O2S:Tb, Dy had emission in the 400–650 nm and the prepared scintillator screen was appropriate for X-ray imaging [4,5]. They reported that adding the appropriate amount of Dy to Gd2O2S:Tb can improve emission efficiency. Also, Yasuda et al. synthesized Gd2O2S: Tb scintillator with different grain sizes for neutron imaging [7]. They showed that the grain size of scintillation powder and amount of binder were affective on image resolution. Lian et al. developed a new method
* Corresponding author. E-mail addresses: [email protected], [email protected] (K.R. Ebrahim Saraee). https://doi.org/10.1016/j.jlumin.2019.116979 Received 26 October 2019; Received in revised form 16 December 2019; Accepted 17 December 2019 Available online 24 December 2019 0022-2313/© 2019 Elsevier B.V. All rights reserved.
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
purification. In a typical synthesis, 10 ml of Gd(NO3)3.6H2O (0.5 M) and 10 ml of Sm(NO3)3.6H2O (0.01 M) were mixed and diluted in 400 ml of 95 � C deionised water. Also, 30 g of urea was weighed and dissolved in 120 mL of 95 � C deionised distilled water. The temperature of the mixture was kept more than 95 � C. Next, the urea solution slowly and drop wisely was added to the gadolinium and the samarium nitrate mixture until precipitation was completed. The mixture was kept stir ring for 1.5 h at more than 95 � C temperature. At the end of stirring, the mixture left for 24 h at room temperature. Next, the white precipitation was separated by centrifuge (5000 rpm, 5 min) and washed several times with deionised water and ethanol. The white precursor powder was dried in an oven at 100 � C for 24 h. The white precursor was ob tained at 100 � C was annealed at 620 � C for 1 h to obtain nanocrystalline Gd2O3:Sm powder. Next, nanocrystalline Gd2O2S:Sm powder was ob tained by annealing Gd2O3:Sm powder with two different concentra tions of sulfur powder. To prepare Gd2O2S:Sm(1) powders, the weight of sulfur powder was 5 times more than the weight of gadolinium oxide and for synthesizing Gd2O2S:Sm(2) powders it was equal. The prepared white powder of the previous step (gadolinium oxide prepared at 620 � C) was mixed with sulfur and heated in a sealed quartz container (about 500 ml) at 900 � C for 1 h purged and filled with an argon atmosphere. The cooling process was done at room temperature. The Gd2O2S:Sm(1) powder which was prepared with a high concentration of sulfur had a gray colour. The Gd2O2SO4:Sm powder was obtained by heating the mixture of the high concentration of sulfur powder and white powder of gadolinium oxide (prepared at 620 � C) in a ceramic crucible inside of the closed steel tube (1.5 m long, 3 inch diameter) and atmospheric condition. The screens from nanocrystalline Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S: Sm(2) and Gd2O2SO4:Sm powders were prepared for using them in X-ray induced emission by coating uniformly on glass substrates. The size of the glass substrates was 1.8 � 1.8 cm2 and 0.13 cm thickness. The coating solution was prepared by nano phosphor powders, polyvinyl alcohol (PVA) and deionised water. First, 5.5% (weight percent) PVA was dissolved into deionised water at a temperature of more than 90 � C. Then, 120 mg of nano phosphor powders were added to the above cool solution and stirred vigorously. Next, all mixtures were poured into a vertical cylindrical tube that the glass substrate was at the bottom. When the sedimentation process was completed, the coated substrate was removed from vertical the cylindrical tube and was dried at room tem perature. The prepared scintillator screen is shown in Fig. 1. The screen coating thickness (mg/cm2) was calculated by equation (1) [4]:
Fig. 1. Scintillation screen used in X-ray luminescence examination.
to prepare red emitter of Gd2O2SO4:Eu because they found out that Gd2O2SO4:Eu has good thermal stability and also a good red light emission when excited under X-ray or ultraviolet light [8,9]. Also, there is a lot of researches that shows scientists are developing Gd2O2S:Tb, Gd2O2S:Eu and Gd2O2S:Pr with other co-doped rare earth to improve luminescence properties and better application. Mochiki et al. used the Gd2O2S:Tb and Gd2O2S:Eu scintillators and introduced a new scintil lator base on different light emissions that were a characteristic property of Tb and Eu. They used two colour scintillator for discrimination of gamma and neutron in the mixed radiation field [5,7–10]. In 2006 and 2017, Dosev et al. and Boopathi et al. studied Gd2O3 doped Sm in the form of nanopowders and nanorods, respectively [3,11]. They used co-precipitation technique and spray pyrolysis method to prepare the Gd2O3:Sm. They prepared nanopowders (5 at.% Sm) and nanorods (20 at.% Sm) of Gd2O3:Sm with 50 nm dimension and 110–420 nm length (50–90 nm diameters), respectively. The structural properties of Gd2O3: Sm were investigated in detail and photoluminescence properties were reported. They reported that Gd2O3:Sm had a good photoluminescence spectrum in the 300–800 nm and band gap of more than 4eV. Fewer reports can be found about Gd2O2S and Gd2O2SO4 which were doped by Sm and most of the papers reported on luminescence properties of micro crystalline and nano crystalline phosphors except the Gd2O2S:Sm and Gd2O2SO4:Sm [2–9]. Increasing the quality of detection of high and low energy radiation and having display devices with better resolution, phosphors with higher scintillation properties such as higher lumines cence efficiency, modified morphology, particle size, and distribution are needed [5]. In this research, the radio- and thermo-luminescence properties of the Sm doped gadolinium oxide, oxysulfide and oxy sulfate compounds that well distributed in morphology were studied in detail. The doping percentage of samarium was maintained to 2 mol% because the goal of this study was an investigation of the effect of different hosts of gadolinium oxide, oxysulfide and oxysulfate on the luminescence properties. Here, the luminescence properties of prepared phosphors with uniform spherical morphology and crystallite size less than 30 nm were studied on the qualitative discussion.
E ¼ ðm1 m2 Þ=S
(1)
where E is the screen coating density and S is the substrate area (in cm2), m1 and m2 are the masses of the screen after and before sedimentation (in mg), respectively. 2.2. Characterization The nanocrystalline powders were characterized by X-ray powder diffraction (XRPD) using a Bruker D8 Advance X-ray powder diffrac tometer (Cu-Kα, λ ¼ 1.5406 Å with Ni filter) to determine the crystal phase and size. To determine the shape and size of the nanocrystalline powder, scanning electron microscopy (SEM) images were obtained with a VEGA, TESCAN SEM (TESCAN, Brno, Czech Republic) which equipped with an XMU unit for energy dispersive X-ray spectroscopy to confirm the presence of impurities in the samples. The Fourier transform infrared (FT-IR) and ultraviolet–visible (UV–Vis) absorption spectra were recorded with a JASCO spectrometer, FTIR-6000 and V-670 models, respectively. The radioluminescence (RL) spectra of samples under X-ray excitation were measured using the high sensitivity spec trometer (Aurora 4000) coupled with an ASENWARE X-ray generator (XJ10-60 N model, Cu anode). To avoid direct X-ray exposure of CCD detectors, the scintillation light was measured by feeding into the
2. Experimental 2.1. Method of preparation of nanocrystalline powders Nanocrystalline Gd2O3:Sm (2 mol%), Gd2O2S:Sm (2 mol%) and Gd2O2SO4:Sm (2 mol%) powders were prepared by the urea homoge neous precipitation method. The raw materials of Gd(NO3)3.6H2O (99.9%, Sigma–Aldrich), Sm(NO3)3.6H2O (99.9%, Exir), urea (99.5%, Merck), and sulfur (99%, Merck) were purchased and used without 2
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
Fig. 2. (a) The Gd2O3:Sm, (b) and (c) Gd2O2S:Sm (high and low sulfur concentration, respectively) and (d) Gd2O2SO4:Sm nanocrystalline X-ray diffraction patterns.
Fig. 3. Determination of the lattice parameters for (a) the Gd2O3:Sm and (b) Gd2O2S:Sm (high sulfur concentration) nanocrystalline powders.
spectrometer through a 2 m optical fibre. All measurements were per formed at room temperature. The RL emission spectra were corrected using a detector correction curve. Also, all nanocrystalline powders were exposed to different times 1, 5, 7 and 12 min of X-rays (V ¼ 40 kV and I ¼ 40 mA) and then the glow curves of them were recorded by an IAP7103 TLD Reader (Institute of Applied Physics, Tehran, Iran).
3. Result and discussion 3.1. XRD study Fig. 2(a)–(d) show the XRD patterns obtained for Gd2O3:Sm, Gd2O2S: Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline powders, respectively. In order to compare the prepared nanocrystalline powders with their pure structure; the reference patterns are shown in figures 3
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Journal of Luminescence 220 (2020) 116979
agreement with the standard data in JCPDS card No. 29–613 and fitted with the orthorhombic structure. No impurity phases were present in the XRD patterns, thereby demonstrating that all of the nanocrystalline powders were prepared with high purity. The strongest diffraction peaks in diffraction patterns were used to calculate the crystallite size using the Debye-Scherrer equation, equation (2):
Table 1 Crystallite size and lattice parameters of the nanocrystalline powders. Sample
Gd2O3 Gd2O2S (high sulfur concentration) Gd2O2S (low sulfur concentration) Gd2O2SO4
DebyeSherer
Lattice parameters
D (nm)
JCPDS (Å)
Calculated(Å)
11 21
a ¼ 10.813 a ¼ 3.852 c ¼ 6.667 a ¼ 3.852 c ¼ 6.667 a ¼ 4.062 b ¼ 4.188 c ¼ 12.960
a ¼ 10.753 a ¼ 3.830 c ¼ 6.501 a ¼ 3.831 c ¼ 6.642 a(103) ¼ 4.0138 b(011) ¼ 4.1419 c(002) ¼ 12.808
19 17
D ¼ kλ=βcos θ
(2)
where D is the average grain size of nanocrystalline powder, k (0.9) is the shape factor and constant value, λ, is the X-ray wavelength (1.5406 Å),βis the full width at half maximum (FWHM) and θis the diffraction angle of an observed peak in a diffraction pattern. The average crys tallite size was obtained approximately 11, 21, 19 and 17 nm for Gd2O3: Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline powders, respectively. Also, the results showed the procedure of prep aration of Gd2O2S was affected on the crystallite size as with decreasing concentration of sulfur a decrease of crystallite size of nanocrystalline Gd2O2S powder was observed. The Nelson–Riley method can be used to interpret X-ray diffraction spectra. In the cubic and hexagonal struc tures, the lattice constants a and c can be calculated by Nelson–Riley method using equation (3): � �� � � 1 cos2 θ cos2 θ f ðθ ¼ þ (3) 2 sin θ θ
(standard data available, JCPDS card No. 12–797, 26–1422 and 29–613). All diffraction patterns of nanocrystalline powders matched well with the standard data in the JCPDS card. The position and in tensity of peaks in the XRD pattern of Gd2O3:Sm was an agreement with standard data of JCPDS card No. 12–797 and peaks fitted with a Bodycentred cubic and space group of Ia3. The XRD patterns of Gd2O2S:Sm (1) and Gd2O2S:Sm(2) were an agreement with the standard data in JCPDS card No. 26–1422 and also fitted with the hexagonal structure (space group P3-m1). The XRD pattern of Gd2O2SO4:Sm was an
Fig. 4. The FTIR spectra of (a) the Gd2O3:Sm, (b) Gd2O2S:Sm and (d) Gd2O2SO4:Sm nanocrystalline powders. 4
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Journal of Luminescence 220 (2020) 116979
Fig. 5. SEM images of (a) the Gd2O3:Sm, (b) and (c) Gd2O2S:Sm (high and low sulfur concentration, respectively) and (d) Gd2O2SO4:Sm nanocrystalline powders.
Fig. 3 (a) and (b) show calculated lattice constants for nanocrystal line Gd2O3:Sm and Gd2O2S:Sm(1) powders. The lattice constant is determined from the intercept of a linear plot of the Nelson-Riley equation versus the lattice parameter. Also, the lattice constants for Gd2O2SO4:Sm nanocrystalline powder was calculated for the deter mined index Miller plane ((103), (011), (002)). The results of lattice parameters and crystallite size of all nanocrystalline powders were re ported in Table 1. All nanocrystalline powders had crystallite sizes of less than 30 nm. The nanocrystalline Gd2O2S:Sm and Gd2O2SO4:Sm powders (prepared at 900 � C) had a bigger crystallite size than their precursor (Gd2O3:Sm prepared at 620 � C) that showed probably changing the crystal structure or annealing temperature were effective on crystallite size. The Gd2O3:Sm nanocrystalline powder and the Gd2O2S:Sm(1) nanocrystalline powder had the smallest and the biggest crystallite size, respectively.
intensity exist in the Gd2O2S and Gd2O2SO4 spectra. The band absorp tion with more intensity around 550-1500 cm 1 in the Gd2O2SO4 spectrum assigned to SO4 2 that confirms gadolinium oxysulfate was formed. The absorption band about 350–550 cm 1 assigned to the vi bration of Gd–O and Gd–S that confirms Gd2O3, Gd2O2S and Gd2O2SO4 formation [2,4]. 3.3. SEM and EDX studies The surface morphology and particle size of nanocrystalline Gd2O3: Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm powders are shown in Fig. 5(a)–(d), respectively. The SEM images of the nano crystalline powders showed the semi-spherical shapes and tended to agglomeration. The nanocrystalline Gd2O2S:Sm and Gd2O2SO4:Sm powders inherited the morphology of Gd2O3:Sm (precursor prepared at 620 � C) and the particle size was almost uniform. The size of the par ticles was varied from 20 nm to 40 nm. By increasing sulfur concen tration to the precursor of Gd2O3 during the Gd2O2S preparation an increase in the agglomeration tendency was observed (compare Fig. 5(b) and (c)). Increasing the annealing temperature to 900 � C was caused that nano particles of Gd2O2SO4:Sm were a little bigger than nano particles of Gd2O3:Sm and agglomeration tendency was decreased, too. EDX anal ysis of nanocrystalline powders confirmed the elemental composition of the powders (Fig. 6 (a)–(c)). The presence of constituent elements of nanocrystalline powders that consist of gadolinium (Gd), oxygen (O),
3.2. FTIR study Fig. 4 (a)–(c) show the FT-IR spectra of Sm doped Gd2O3, Gd2O2S(1) and Gd2O2SO4, respectively. The FT-IR spectra of Sm doped Gd2O2S(1) and Gd2O2S(2) were the same. In all Fig. 4 (a)–(c), the broad absorption band around 2800-3800 cm 1 can be assigned to O–H stretching vi bration of absorbed water from the air. The band around 750-2000 cm 1 in the Gd2O3 spectrum assigned to C–O and CO3 2 vibration and disap pears in high annealing temperature. Also, these bands with less 5
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Journal of Luminescence 220 (2020) 116979
Fig. 6. The EDX spectrum of (a) the Gd2O3:Sm, (b) Gd2O2S:Sm (high concentration) and (c) Gd2O2SO4:Sm nanocrystalline powders.
Fig. 7. UV–Visible absorbance spectra of the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm.
sulfur (S) and samarium (Sm) elements was investigated for each syn thesized nanocrystalline powders. Also, it was observed carbon peaks with low intensity. It is disappearing at higher annealing temperature.
3.4. UV–visible study Fig. 7 illustrates the UV–Visible absorption of nanocrystalline Gd2O3: 6
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Journal of Luminescence 220 (2020) 116979
Fig. 8. The radioluminescence spectrum of the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm screens.
related to the host crystal, the energy transfer of an electron from 2p or 3p orbital of O2 and S2 to the 5d orbital of Gd3þ ion [12]. This band for nanocrystalline Gd2O2S:Sm powders was broader in compared to the absorption band for nanocrystalline Gd2O3:Sm and Gd2O2SO4:Sm powders. It seems that the maximum absorption intensity for nano crystalline Gd2O3:Sm and Gd2O2SO4:Sm powders went to a shorter wavelength. The data of optical absorption spectra and Tauc equation were used to obtain the band gap values. The band gap of nanocrystal line powders was obtained approximately 5.02, 4.12 and 5.08 eV for Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm, respectively. The strong ab sorption band shows that the band gap of all nano crystalline powder is approximately more than 4 eV and the band gap of Gd2O3:Sm and Gd2O2SO4:Sm are a little more than Gd2O2S:Sm band gap. Also, there was a weak absorption band with low intensity in the UV–Visible ab sorption spectrum only for nanocrystalline Gd2O3:Sm and Gd2O2SO4:Sm powders. It is maybe attributed to have a wider band gap of these phosphors compared to the crystalline Gd2O2S:Sm powders. The weak absorption band around 265 nm and 326 nm have corresponded to the 8 S7/2-6I7/2 and 8S7/2-6P7/2 transitions of Gd3þ ion, respectively [13]. Also, there was a peak with low intensity in the range of 350–700 nm for all nanocrystalline Gd2O3:Sm, Gd2O2S:Sm, and Gd2O2SO4:Sm powders. It may be attributed to the internal f-f absorption transition of Sm3þ ion (maximum intensity related to 6H5/2-6P3/2 energy transition) [13] or because trivalent rare earth ions demonstrate a very narrow band due to the shielding of 4f-orbital by external 5s- and 5p-shells, with most likely, the nature of this band is associated with intrinsic defects of hosts, like oxygen vacancies, for example.
Fig. 9. CIE chromaticity coordinate of the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline phosphors.
3.5. Radio-luminescence and X-ray imaging studies The radioluminescence (RL) examination was done because an X-ray photon can penetrate entire samples and create enormous electrons and holes by exciting electrons from a valence band to conduction band that recombines consequently and allows detecting all possible transitions in the emission spectrum. The X-ray induced luminescence spectra for nanocrystalline Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm powders are shown in Fig. 8. The measurement was done for all prepared screens of nanophosphors in the same condition. The screen thickness density was about 20 mg/cm2. The X-ray of 40 kV and 40 mA was used and the RL spectrum was examined at room tempera ture. All nanocrystalline powders had four emission peaks at 564, 605, 648 and 704 nm which were assigned to 4G5/2-6H5/2, 4G5/2-6H7/2, 4G5/ 6 4 6 3þ ion, respectively 2- H9/2 and G5/2- H11/2 energy transitions of Sm
Fig. 10. The X-ray radiography images obtained for Gd2O2SO4:Sm screen at different irradiation conditions.
Sm, Gd2O2S:Sm, and Gd2O2SO4:Sm powders which showed all nano crystalline powders consisted of a strong absorption band around 220–237 nm, 220–300 nm and 220–247 nm, respectively. The absorp tion band around 220–237 nm, 220–300 nm and 220–247 nm was 7
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Journal of Luminescence 220 (2020) 116979
Fig. 11. Glow curves of (a) all nanocrystalline powders (7min, X-ray irradiation) and, (b) the Gd2O3:Sm, (c) and (d) Gd2O2S (high and low sulfur concentration, respectively) and (e) Gd2O2SO4 nanocrystalline powders irradiated with different times of X-rays.
[14]. The RL emission spectra showed the strongest peak centred at 605 nm and it was the predominant emission peak for all samples. The emission intensity of the energy transition of 4G5/2-6H11/2 was the least for nanocrystalline Gd2O3:Sm powder. It showed that the symmetric cubic structure and the low lattice crystal field of the Gd2O3 were affected energy level separation and then the low intensity of the Sm3þ
emission was caused. The emission spectrum for nanocrystalline Gd2O2SO4:Sm powder showed narrow and sharp peaks and overall the Gd2O2S:Sm and Gd2O2SO4:Sm spectra were a little shifted to lower wavelength in comparison to nanocrystalline Gd2O3:Sm powder. It is maybe attributed to increasing in lattice crystal field and energy level separation due to 8
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Journal of Luminescence 220 (2020) 116979
Fig. 12. Glow curves of (a) the Gd2O3:Sm, (b) and (c) Gd2O2S:Sm (high and low sulfur concentration, respectively) and (d) Gd2O2SO4:Sm nanocrystalline powders were recorded at different heating rates (3, 5, 7K/s).
change the symmetry of the structure of Gd2O2S:Sm and Gd2O2SO4:Sm nano crystals and Sm3þ ion position in the crystal lattice. The maximum and minimum emission intensities were related to nanocrystalline powders of Gd2O2SO4:Sm and Gd2O3:Sm, respectively. Also, the emis sion intensity for nanocrystalline Gd2O2S:Sm(1) was less than Gd2O2S: Sm(2). Probably, the excess sulfur was caused the Gd2O2S:Sm(1) powder turns gray which the gray colour compared to the white colour of Gd2O2S:Sm(2) powder had more self-absorption and was caused a decrease in emission intensity of gray Gd2O2S:Sm(1) powder. Moreover, the RL spectra of Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nano crystalline powders showed a good emission in the range of 400–800 nm that compatible with the most of commercial PMTs and photodiode detectors. CIE chromaticity coordinate of the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline phosphors are shown in Fig. 9. As the RL result showed, different hosts and different concentrations of sulfur were effective on the Sm emission spectrum corresponded to different CIE coordinates in the orange-red emission region. Fig. 10 shows the X-ray radiography images obtained from the screen of Gd2O2SO4:Sm coupled with a radiographic film. Measurements were carried out for different voltage (60 kVp and 64 kVp), same irradiation times and constant current (0.064s, 8 mA, planmeca intra, dental x-ray machine). The optical intensity of dark areas affected by screen scintil lation for 60 kV, 8 mA (0.064s) and 64 kV, 8 mA were 2.1 and 2.77, respectively. Increasing voltage and X-ray energy enhanced the screen
light output and image resolution. 3.6. TL study In order to characterise the trap levels that exist in the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline phosphors, all nano crystals were irradiated with different times (1, 5, 7 and 12 min) of Xrays and the TL glow curves of the irradiated phosphors were recorded at different heating rates in the range of 323–673 K. The TL glow curves obtained for the Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline powders were recorded after 7 min irra diation (40 kV, 40 mA) of X-ray exposure (Fig. 11 (a)). The irradiated nanocrystalline powders were read at a heating rate of 3K/s for 150 s and at a maximum temperature of 673 K. Preheating was applied at 323K. Fig. 11(a) shows that the TL glow curve was obtained for nano crystalline Gd2O3:Sm powder had four peaks near 403, 447, 496 and 619 K. The glow curve for nanocrystalline Gd2O2S:Sm powder was contained two intensive peaks at 407 K and 643 K. Also, the TL glow curve for nanocrystalline Gd2O2SO4:Sm powders was contained two intensive peaks at 413 K and 506 K. The area under the glow curve was obtained 732597, 277560, 1.43 � 106 and 9.21 � 107 counts for Gd2O3: Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline powders in the 323–650 K, respectively. Fig. 11 (b)–(e) show the dose dependence of the TL glow curves for all nanocrystalline phosphorous which were irradiated with different 9
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A.A. Kharieky and K.R. Ebrahim Saraee
Fig. 13. Comparison between the experimental and the fitted TL glow for the 5 min X-ray irradiation (3K/s) (a) the Gd2O3:Sm, (b) and (c) Gd2O2S:Sm (high and low sulfur concentration, respectively) and (d) Gd2O2SO4:Sm nanocrystalline powders. Table 2 Kinetic parameters of the deconvoluted TL glow curves of the Sm doped (a) Gd2O3, (b) and (c) Gd2O2S (high and low sulfur concentration, respectively) and (d) Gd2O2SO4 nanocrystalline samples. peak
Tm(K)
T1(K)
T2(K)
μg
Order of kinetic
Eτ (eV)
Eδ (eV)
Eω (eV)
Eave (eV)
a a
612.40
560.69
664.12
0.50
1.92
0.89
0.97
0.94
0.93
b
502.40
460.59
544.22
0.50
1.92
0.74
0.81
0.78
0.78
c
446.60
423.59
469.62
0.50
1.92
1.16
1.16
1.17
1.16
d
404.00
382.32
425.69
0.50
1.92
1.00
1.01
1.01
1.01
b a
646.40
587.36
705.45
0.50
1.92
0.85
0.94
0.90
0.90
559.93
525.65
594.22
0.50
1.92
1.19
1.22
1.21
1.21
c
489.78
456.41
523.17
0.50
1.92
0.92
0.96
0.94
0.94
d
437.19
414.46
459.93
0.50
1.92
1.12
1.13
1.12
1.12
e
404.31
370.10
438.52
0.50
1.92
0.58
0.64
0.62
0.63
)
1.42 � 106
2.35 � 106
9.46 � 1011 2.77 � 1011
2.80 � 105
3.81 � 109 2.48 � 108
7.16 � 1011 2.06 � 106
FOM ¼ 0.0223 675.63
628.29
722.97
0.50
1.92
1.22
1.29
1.26
1.26
b
588.27
543.17
633.39
0.50
1.92
0.96
1.02
0.99
0.99
c
480.56
427.22
533.92
0.50
1.92
0.49
0.58
0.53
0.53
d
406.65
374.87
438.45
0.50
1.92
0.64
0.69
0.67
0.67
d a
1
FOM ¼ 0.0184
b
c a
S (s
8.89 � 107
1.21 � 107 1.21 � 104 1.13 � 107
FOM ¼ 0.0208 624.49
569.55
679.44
0.50
1.92
0.86
0.95
0.91
0.90
b
503.50
463.26
543.75
0.50
1.92
0.78
0.84
0.81
0.81
c
413.60
384.23
442.98
0.50
1.92
0.74
0.78
0.76
0.76
FOM ¼ 0.0236
10
6.04 � 105
5.58 � 106 1.04 � 108
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
times of X-rays (1, 5, 7 and 12 min). Almost the shape of the TL glow peaks was not changed significantly with increasing time of X-ray irra diation. By increasing the time of irradiation and X-ray doses, the in tensity of the TL glow peaks was increased and the position of peaks was shifted toward lower temperatures (more than 8 K for all glow curves of nano phosphors). By increasing the irradiation time and X-ray doses, the number of trapping centres and the creation of electron-hole pairs was increased and the intensity of peaks in each glow curve was increased. The TL glow peaks were obeyed second-order kinetics because with increasing the X-ray doses, the peaks were shifted to a lower tempera ture and the shape of the glow curve was not changed, [15]. Also, the TL glow curves of all Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline phosphors were recorded at different heating rates (3, 5, 7 K/s) for 5 min irradiation of X-rays (Fig. 12). With increasing the heating rate, a shift in a peak position, more than 6 K, to higher temperature was recorded and an increase in TL intensity was observed. These results also indicated that the second-order kinetics is a good method to analyze the glow curves [15]. The trap levels of the Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline phosphors which are in the band gap were characterized by order of kinetics, trap depth or activation energy and frequency factor. In the present research, trapping parameters were determined by the computerized glow curve deconvolution (CGCD) method base on the shape of the glow curve of samples and the order of kinetics for the TL glow peaks for all samples. For this purpose, the Chen formula was used, Eα ¼ cα (kT2m/α) – bα (2kTm), where k is Boltzmann constant (8.6 � 10 5 eVK 1), α ¼ τ, δ, ω and cτ ¼ 1.51 þ 3.0(μg-0.42), cδ ¼ 0.976 þ 7.3(μg-0.42), cω ¼ 2.52 þ 10.2(μg-0.42) and bτ ¼ 1.58 þ 4.2 (μg-0.42), bδ ¼ 0, bω ¼ 1) [16,17]. In the Chen method, the shape pa rameters were used to determine the order of kinetics. Total half-intensity width (T2-T1) and high temperature half width (T2-Tm) were used for interpretation of the order of kinetics which Tm is the peak of temperature at maximum intensity and T1 and T2 are the tempera tures on either side of Tm. Chen used a symmetry factor (μg¼(T2-Tm)/(T2-T1)) to identify the first- and second-order of the ki netics of TL glow curves. The symmetry factor lies between 0.37 and 0.56 which is close to 0.42 for first order kinetics and 0.52 for second order kinetics [18]. All TL glow curves of the Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nanocrystalline samples were decon voluted using the origin software program in order to obtain isolated peaks (Fig. 13). The calculated FOM values were less than 2.5%, it means fitted peaks were matched well and good agreement with experimental data. Then, the trapping parameters of each sample were determined for each deconvoluted peak. The order of kinetics for each deconvoluted peak was close to second order kinetics (μg ¼ 0.5). All detail about trapping parameters of the deconvoluted peaks for the Gd2O3:Sm, Gd2O2S:Sm(1), Gd2O2S:Sm(2) and Gd2O2SO4:Sm nano crystalline phosphors were summarized in Table 2 (a)–(d). All the deconvoluted peaks in all glow curves were found to obey second-order kinetics that indicating the retrapping phenomena of charge carriers were occurring.
temperatures with increasing doses and confirmed second order kinetics behaviour. Trapping parameters were investigated and calculated from TL data using glow curve analysis and computerized glow curve deconvolution (CGCD) method. The glow curve examination showed that the shape of the glow curve of Gd2O2S:Sm and Gd2O2SO4:Sm nano phosphors were changed and completely different than their precursors (Gd2O3:Sm). The calculated activation energy of Gd2O2S:Sm and Gd2O2SO4:Sm nano phosphors showed that these nano phosphors had deeper trap centres in comparison to Gd2O3:Sm nano phosphor. Also, The X-ray induced luminescence results of Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline powders showed a good emission in the range of 400–800 nm that compatible with the most of commercial PMTs and photodiode detectors. The X-ray induced luminescence results showed that the Gd2O2SO4:Sm nanocrystalline powder for the same weight of host material and the same doping level of Sm had the most emission intensity. The X-ray imaging results showed that the screen of Gd2O2SO4:Sm nano phosphor is suggested for the scintillation applica tion and can be an appropriate choice for the X-ray imaging applica tions. Also, the Gd2O2SO4:Sm nanocrystalline powder could be used in integration mode as a scintillator in medical and industrial X-ray digital imaging inspection systems with more scintillation efficiency in com parison to Gd2O3:Sm, Gd2O2S:Sm nanocrystalline powders at the same application. CRediT authorship contribution statement Amin Aghay Kharieky: Investigation, Methodology, Project administration, Resources, Software, Writing - original draft, Validation, Visualization. Khadijeh Rezaee Ebrahim Saraee: Conceptualization, Data curation, Formal analysis, Funding acquisition, Supervision, Vali dation, Visualization, Writing - review & editing. References [1] X. Yan, G.R. Fern, R. Withnall, J. Silver, Effects of the host lattice and doping concentration on the colour of Tb3þ cation emission in Y2O2S:Tb3þ and Gd2O2S:Tb3 þ nanometer sized phosphor particles, Nanoscale (2013), https://doi.org/10.1039/ c3nr01034a. [2] S.A. Osseni, Yu G. Denisenko, J.K. Fatombi, E.I. Salnikova, O.V. Andreev, Synthesis and characterization of Ln2O2SO4 (Ln ¼ Gd, Ho, Dy and Lu) nanoparticles obtained by coprecipitation method and study of their reduction reaction under H2 flow, J. Nanostruct. Chem. (2017), https://doi.org/10.1007/s40097-017-0243-4. [3] G. Boopathi, S. Gokul Raj, G. Ramesh Kumar, R. Mohan, S. Mohan, Synthesis of samarium doped gadolinium oxide nanorods, its spectroscopic and physical properties, Indian J. Phys. (2018), https://doi.org/10.1007/s12648-017-1158-0. [4] A. Bagheri, Kh Rezaee Ebrahim Saraee, H.R. Shakur, H. Zamani Zeinali, Synthesis and characterization of physical properties of Gd2O2S:Pr3þ semi-nanoflower phosphor, Appl. Phys. A (2016), https://doi.org/10.1007/s00339-016-0058-z. [5] Kh Rezaee Ebrahim Saraee, M. Darvish Zadeh, M. Mostajaboddavati, A. Aghay Kharieky, Changes of Tb emission by non-radiative energy transfer from Dy in Gd2O2S:Tb Phosphor, J. Electron. Mater. (2016), https://doi.org/10.1007/s11664016-4639-6. [6] Z. Luo, J.G. Moch, S.S. Johnson, C.C. Chen, A review on X-ray detection using nanomaterials, Curr. Nanosci. (2017), https://doi.org/10.2174/ 1573413713666170329164615. [7] R. Yasuda, M. Katagiri, M. Matsubayashi, Influence of powder particle size and scintillator layer thickness on the performance of Gd2O2S:Tb scintillators for neutron imaging, Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrom. Detect. Assoc. Equip. (2012), https://doi.org/10.1016/j.nima.2012.03.035. [8] S. Blahuta, B. Viana, A. Bessiere, E. Mattmann, B. La Course, Luminescence quenching processes in Gd2O2S:Pr3þ,Ce3þ scintillating ceramics, Opt. Mater. (2011), https://doi.org/10.1016/j.optmat.2011.02.040. [9] J. Lian, F. Liu, X. Wang, X. Sun, Hydrothermal synthesis and photoluminescence properties of Gd2O2SO4:Eu3þ spherical phosphor, Powder Technol. (2014), https:// doi.org/10.1016/j.powtec.2013.11.021. [10] K. Mochiki, Y. Murata, K. Nittoh, Neutron gamma ray radiography using a twocolor luminescent scintillator, Appl. Radiat. Isot. (2004), https://doi.org/10.1016/ j.apradiso.2004.03.074. [11] D. Dosev, I.M. Kennedy, M. Godlewski, I. Gryczynski, K. Tomsia, E.M. Goldys, Fluorescence upconversion in Sm-doped Gd2O3, Appl. Phys. Lett. (2006), https:// doi.org/10.1063/1.2161400. [12] R. Manigandan, K. Giribabu, R. Suresh, S. Munusamy, S. Praveen kumar, S. Muthamizh, T. Dhanasekaran, A. Padmanaban, V. Narayanan, Synthesis, growth and photoluminescence behaviour of Gd2O3SO4:Eu3þ nanophosphors: the effect of temperature on the structural, morphological and optical properties, RSC Adv. (2015), https://doi.org/10.1039/C4RA13897J.
4. Conclusion The Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm semi-spherical nano crystalline phosphors were successfully synthesized through the modi fied method by urea homogeneous precipitation method. The characterized nanocrystalline powders results confirmed that all the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nanocrystalline powders synthesized had cubic, hexagonal and orthorhombic structure and had uniform mean size of about 30 nm diameters. The strongest orange-red emission peak by X-ray excitation was observed located at 605 nm for the Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nano particles which correspond to the 4G5/2-6H7/2 transition of the Sm3þ ions. The thermo luminescence (TL) studies on Gd2O3:Sm, Gd2O2S:Sm and Gd2O2SO4:Sm nano particles showed a shifting of the peaks towards lower 11
A.A. Kharieky and K.R. Ebrahim Saraee
Journal of Luminescence 220 (2020) 116979
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