Photoluminescence, thermoluminescence glow curve and emission characteristics of Y2O3:Er3 + nanophosphor

Accepted Manuscript Photoluminescence, Thermoluminescence glow curve emission characteristics of Y2O3:Er3+ nanophosphor

and

N.J. Shivaramu, B.N. Lakshminarasappa, K.R. Nagabhushana, H.C. Swart, Fouran Singh PII: DOI: Reference:

S1386-1425(17)30629-7 doi: 10.1016/j.saa.2017.07.070 SAA 15357

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received date: Revised date: Accepted date:

25 March 2017 21 June 2017 31 July 2017

Please cite this article as: N.J. Shivaramu, B.N. Lakshminarasappa, K.R. Nagabhushana, H.C. Swart, Fouran Singh , Photoluminescence, Thermoluminescence glow curve and emission characteristics of Y2O3:Er3+ nanophosphor, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2017), doi: 10.1016/j.saa.2017.07.070

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ACCEPTED MANUSCRIPT Photoluminescence, Thermoluminescence glow curve and emission characteristics of Y2O3:Er3+ nanophosphor N.J. Shivaramu1*, B.N. Lakshminarasappa2*, K.R. Nagabhushana3, H.C. Swart1, Fouran Singh4 Department of Physics, University of the Free State, Bloemfontein, ZA-9300, South Africa 2 Department of Physics, Bangalore University, Bangalore- 560 056, India 3 Department of Physics, PES University, Bangalore-560085, India 4 Inter University Accelerator Centre, P.O. Box No. 10502, New Delhi 110 067, India

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*Corresponding author: Tel: +91 9448116281 (Dr. B.N. Lakshminarasappa). Email: [email protected] (Dr. B.N. Lakshminarasappa), [email protected] (Dr. N.J. Shivaramu).

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Abstract

Nanocrystalline Er3+ doped Y2O3crystals were prepared by a sol gel technique. X-ray diffraction

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(XRD) patterns showed the cubic structure of Y2O3 and the crystallite size was found to be ~25 nm. Optical absorption showed absorption peaks at 454, 495 and 521 nm. These peaks are

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attributed to the 4F3/2+4F5/2, 4F7/2 and 2H11/2+4S3/2 transitions of Er3+. Under excitation at 378 nm, the appearance of strong green (520-565 nm) down conversion emission assigned to the (2H11/2, S3/2)→4I15/2 transition and the feeble red (650-665 nm) emission is assigned to the 4F9/2→4I15/2

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transition. The color chromaticity coordinates showed emission in the green region. The strong

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green emission of Y2O3:Er3+ nanophosphor may be useful for applications in solid compact laser devices. Thermoluminescence (TL) studies of γ-irradiated Y2O3:Er3+showed a prominent TL

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glow peak maximum at 383 K along with a less intense shoulder peak at ~425 K and a weak glow at 598 K. TL emission peaks with maxima at 545, 490, 588 and 622 nm for the doped

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sample were observed at a temperature of 383 K and these emissions were due to defect related to the host material. TL kinetic parameters were calculated by a glow curve deconvolution (GCD) method and the obtained results are discussed in detail for their possible usage in high dose dosimetry.

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ACCEPTED MANUSCRIPT Keywords:

Oxide

materials;

Sol-gel

process;

Radiation

effects;

X-ray diffraction;

Photoluminescence; Thermoluminescence. 1. Introduction Nanostructured materials have attracted enormous attention by a large number of researchers, because of their greater unique properties when compared to bulk materials. Extensive research has been carried out to improve efficiency of rare earth activated oxide phosphors due to their

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superiority in color purity as well as thermal, chemical and radiative stabilities [1-3]. Rare earth

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(RE) oxides have attracted a lot of attention in the last few decades [4, 5]. Among these yttrium

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oxides is a promising host material due to its high band gap, low phonon energy, high chemical, thermal and radiation stability. Therefore RE doped yttrium oxide is largely used in

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optoelectronics, display materials and dosimetry applications. Meanwhile, optical properties of Er3+ doped Y2O3 nanophosphor have enticing great interest in terms of up-conversion lasers,

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fiber telecommunications and displays materials [6].

Thermoluminescence (TL) is a powerful technique to study the nature of defects and

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measurement of energetic radiation dose in solids. TL is highly structure sensitive, simple, a consistent technique and has broad applications in diagnostic and therapeutic purposes,

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geological dating, etc. Nowadays energetic radiations are measured largely by using a thermoluminescent dosimetry (TLD) badge. There is a number of techniques to study TLD

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materials and their TL behavior by gamma, UV, beta and swift heavy ion beam irradiation [710]. Gamma induced modification of RE doped TLD has been widely studied from the past few

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decades [11, 12]. Gamma radiation can create vacancies (oxygen vacancies), interstitial defects and defect clusters. These defects are trapped below the conduction band and above the valence

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band in the band gap of a material. These defects absorbs thermal energy from external sources and then these defects are moving to the conduction band and recombine with opposite charge of the free particles (electrons/holes) or the same conduction electrons are retrapped at intermediate levels of the band gap, resulting in the emission of the TL signal. Althought there exists a number of excellent dosimetric nanophosphors [13, 14] there is still a great interest in searching

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ACCEPTED MANUSCRIPT for good dosimetric materials for radiation dose assessment in environment, reactor places and outer space. [15-17]. Various methods have been employed to synthesize Y2O3:Er3+, viz the co-precipitation [18], spray pyrolysis [19], sol–gel [20], combustion [21], hydrothermal method [4] and chemical vapor deposition [22]. Each method results in different morphologies and particle sizes which affects the luminescence properties. Among these techniques the sol-gel process is also known as

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the wet chemical technique; it is widely used in the field of materials science and engineering.

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This method is useful for the synthesis of nanomaterials at low temperatures. In addition, high

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homogeneous, multi-compounds, single phase, spherical and fibrils of the controlled material are obtained. The sol-gel approach is a cheap and low temperature technique that produces the fine

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control of the size and shape and large surface to volume ratio products. [23]. In the present work we report on the synthesis, the systematic studies on structural, PL properties, TL glow curve,

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TL emission and dosimetric behavior of gamma irradiated Er3+ doped Y2O3 nanophosphor. 2. Experimental

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Nanophosphor Y2O3:Er3+ was prepared by a sol gel technique at low temperature. Yttrium (III)

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nitrate hexahydrate [99.8% pure (Y (NO3)3 6H2O), Aldrich chemicals], erbium nitrate pentahydrate [99.9 % pure (Er (NO3)3 5H2O), Aldrich chemicals], citric acid anhydrous [99.5%

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pure GR (C6H8O7), Merck chemicals] and 25 % ammonia solution [GR (NH3), Merck chemicals] were used as starting raw materials. The ratio of citric acid to Y3+ was taken as 2.0 [25, 25].

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Stoichiometric amounts of yttrium nitrate were dissolved in double distilled water and then the solution was stirred at room temperature for 2 h. The stoichiometric amount of erbium nitrate

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was added into the yttrium nitrate precursor solution. The solution was stirred at 70 °C for 2 h and then stoichiometric amount of citric acid was added slowly, which acts as a complexing/chelating agent and again it was stirred at 75–80 ℃ for 2 h. Then the pH was adjusted to 2 by adding 25% aqueous ammonia solution. The obtained solution was stirred at the same condition for 6 h. Finally, it turned into a reddish brown gel. The gel was dried at 110 ℃for

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ACCEPTED MANUSCRIPT 12 h in an oven to obtain a powder and the obtained powder was annealed at 900 ℃ for 2 h to remove the impurities if any [26]. The annealed samples were characterized by using x-ray diffraction (XRD), measured using an advanced D-8 X-ray diffractometer (Bruker AXS Germany) using 1.5406Å CuKα radiations. The morphology was studied by a field emission scanning electron microscope (FE-

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SEM) [MIRA II LMH from TESCAN] equipped with an Energy dispersive analysis X-ray

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spectroscopy (EDAX) technique. The optical absorption of pure and Er3+ doped Y2O3 samples

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was carried out using a UV–VIS using an Ocean optics USB 4000, charged coupled detector (CCD) spectrophotometer. PL measurements were performed on a F-2700 FL spectrophotometer equipped with a 700 W xenon lamp as an excitation source. TL glow curves of Y2O3:Er3+ were

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recorded using a Harshaw TLD reader (model 3500) in the temperature range of 323–673 K at an heating rate of 5 Ks-1. The obtained TL glow curves were deconvoluted using the glow curve

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deconvoluted (GCD) technique. TL emission carried out using a TL Reader (model: TL1009I; Nucleonix Systems Pvt Ltd, India) in the temperature range of 323-750 K at an heating rate of 5

3. Results and discussion

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3.1 X-ray diffraction

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Ks-1 by connecting the Ocean Optics spectrometer (USB4000).

Figure 1(a) shows the XRD patterns of the 900 ℃ annealed undoped and Er3+ (0.2, 0.6 and 1.0

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mol %) doped Y2O3. It is confirmed that all the diffraction peaks exhibit the cubic phase with the space group Ia3̅. No other/impurities phases are observed in the undoped and doped samples.

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Lattice parameters of the unit cell were a=b=c=10.611 Å with α=β=γ=90° and the obtained values were well matched with the JCPDS database 88-1040 [27]. With the addition of the different Er3+ concentrations, the diffraction peak positions did not altered. This indicates that Er3+ doping ions have been incorporated into the Y3+ lattice in the Y2O3 crystal system. It is revealed that the incorporation of Er3+ions into Y3+ sites do not alter the cubic crystal structure. It is due to similar ionic radii of Y3+ (~0.90 Å) and Er3+ (~0.89 Å). Structural parameters such as 4

ACCEPTED MANUSCRIPT lattice constants (a), cell volume (V), inter-planar spacing (d), density (Dx) and dislocation density (δ) were calculated from the XRD patterns and are tabulated in Table 1. The peak at 2θ~ 29.4◦ is the strongest one assigning to the (222) plane. The average crystallite (D) size was found to be in the range of 24–26 nm for the doped and 31 nm for the undoped samples calculated using the Scherrer’s equation [12]. It was also observed that, the average crystallite sizes did not perturbed with an increasing Er3+ dopant concentration. The microstrain (ε) and crystallite size

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were also calculated using the Hall and Williamson equation [12]. Figure 1(b) shows the plot of

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βcosθ versus sinθ for all the undoped and doped phosphors. The reciprocal of the Y-intercept

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(βcosθ axis) gives the average crystallite size. The slope of this straight line gives the lattice microstrain. The microstrain occurred due to presence of crystal imperfection and stress in a

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crystal. The obtained microstrain is also given in Table 1. The micro strain produces broadening of the XRD peaks [28]. It was observed that the crystallite size slightly increased with the Er3+

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concentration and the microstrain vary slightly in a random way after doping. Therefore it revealed that the dopant did not really affect the crystal structure due to the Er3+ ion occupied

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the Y3+ sites in the host lattice structure.

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Rietveld refinement

Figure 1(c) and 1(d) shows the Rietveld refinement of Y2O3 and Y2O3:Er3+ nanophosphor

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performed with the FULLPROF Program [28]. It was performed to analyze the structure and unit cell of the samples. Table 2 represents the structural refinement results for the synthesized Y2O3

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and Y2O3:Er3+ nanophosphors. The results confirmed a good agreement between the observed and fitted XRD patterns. The parameters of Bragg's contribution (χ2) and the goodness of fit

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(GOF) are giving the quality of the structural refinement [12], these values were found to be less than 5 and close to 1. It is indicating a good fit between the calculated and observed XRD patterns. The calculated values of the lattice constant are closed to the Rietveld refinement values and these values are well matched with the standard data [27]. A little variation of the occupancy of O1, Y1 and Y2 were observed in the Er doped Y2O3 when compared with the undoped material; it was due to the incorporation of the Er3+ instead of the Y3+sites. 5

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3.2 Field emission scanning electron microscopy Figure 2(a) shows the FE-SEM image of the 900℃ annealed Y2O3:Er3+. This indicates the particles were well separated with a spherical shape. The morphology of the samples depended on the synthesis temperature, annealing temperature, pH value and concentration of organic

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agent. SEM micrograph shows pores and voids in the sample, which can be ascribed to the large

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amount of gases that have escaped from the sample during the drying process. The average grain

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size was estimated to be 30 nm. Energy dispersive analysis X-ray spectroscopy (EDAX) technique confirmed the presence of Y, O and Er elements in the synthesized sample is shown in

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Figure 2(b).

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3.3 UV-Visible absorption

Figure 3(a) shows the optical absorption spectra of the Y2O3 and Y2O3:Er3+ nanophosphor in the

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wavelength range of 200–800 nm. The sharp absorption peaks appearing at about 220, 250 and 290 nm were due to the host material. In addition to that the Er3+ doped Y2O3 absorption peaks 2

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are observed at 454, 495 and 521 nm. These peaks are attributed to the 4F3/2+4F5/2, 4F7/2 and H11/2+4S3/2 transitions [29]. In order to estimate the energy gap (Eg) the Tauc-relation i.e. (αE) =

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K(E−Eg)1/n was used, where ‘E’ is the photon energy, ‘α’ is the optical absorption coefficient, ‘K’ is constant and ‘n’ is the optical transition. Figure 3(b) was obtained by plotting (αE)n versus

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E in the high absorption range followed by extrapolating the linear fitted region to (αE)n = 0. It was fitted with the above equation for n = 2, which indicates that the allowed direct transition

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was responsible for the inter band transition in the Y2O3:Er3+ [30]. From Figure 3(b) an energy band gap for Y2O3:Er3+ at 5.1 eV was obtained which was slightly lower than that of the undoped Y2O3 (5.3 eV). This might be due to the morphology and variation of the particle size and the Burstein-Moss effect where the negative shift in the band gap is due to the interactions terms created by adding the extra charges through doping [31]. 6

ACCEPTED MANUSCRIPT 3.4 Photoluminescence Figure 4(a) shows the PL excitation spectrum of the Y2O3:Er3+ nanophosphor recorded in the wavelength range of 200 - 500 nm (λem= 563 nm). The UV range is weak by a broad band with absorption maxima at 257 and 275 nm due to the O2--Er3+ charge transfer band and is shown in the inset of Figure 4(a). Thus, the UV radiation is not efficiently absorbed by this charge transfer

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state, while the lower energy region is dominated by the narrow f-f transitions of the Er3+ ions. A

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strong peak at 378 nm is assigned to the hypersensitive transition 4I15/2 →4G11/2 and other bands with maximum at 408, 454 and 490 nm are assigned from the 4I15/2 ground state to the 4H9/2, 4F3/2

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+ 4F5/2 and 4F7/2 excited states of Er3+ ion transitions respectively [32, 33].

Figure 4(b) shows the down shifting emission spectra of Y2O3:Er3+ (0.1-1.0 mol %)

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nanophosphor under 378 nm excitation. All the spectra show the typical emission peaks of Er 3+ ions in cubic Y2O3. The intense emission peaks observed in the green region 520–565 nm are

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attributed to the (2H11/2, 4S3/2)→4I15/2transitions and weak emission in the red region 650–665 nm is attributed to the 4F9/2→4I15/2 transition of Er3+ ions, respectively. Krzysztof Anders et al. [34],

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reported the emission spectra of polymer composites doped with Y2O3:Er3+nano powders. They observed emission with peaks at 524, 540, 555, 565 and 663 nm which were attributed to the

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transition from the Er3+ ions [34].

Figure 4(b) shows that the green emission at 520-565 nm was more intense than the red

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(650–665 nm) emission. The origin of these transitions (electric dipole or magnetic dipole) from emitting levels to terminating levels depends upon the site where the Er3+ ion is located in the

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Y2O3 cubic crystal system and the type of transition is assigned by the selection rules [35]. The XRD pattern of the Y2O3:Er3+ samples exhibit a cubic C-type crystal structure. The C-type

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structure of Y2O3 has two possible non-equivalent sites for the metal ions, a noncentrosymmetric C2 and a centrosymmetric C3i site. The probability of ratio between the number of metal ions occupying C2 and C3i sites is equal to 3:1. The Y2O3 structure can be described as one Y3+ ion in the center of the cube and six O2- ions occupying the six corners with two vacancies at the corner of the phase diagonal in the C2 symmetry and a body diagonal in the C3i symmetry. It can clearly be seen that the Er3+ occupies most probably the C2 symmetry in the 7

ACCEPTED MANUSCRIPT Y2O3 lattice [34]. Therefore, the electric dipole (ED) transition of the Er3+ ions is from the C2 sites and the magnetic dipole transition is from the C3i-sites. Since, the C3i-sites cannot provide the odd terms in the crystal field [36, 37]. Therefore, Er3+ is suitable to substitute the Y3+ sites giving rise to the intense green and feeble red emission that occurred from the Er3+ ions at the C2 sites emission in all the samples [7].

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Figure 4(c) shows the variation of the PL intensity as a function of the concentration of 3+

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the Er . The PL intensity at 521, 538, 553 and 563 nm were found to increase with dopant concentration up to 0.8 mol% of Er3+ and then decreased with a further increase of the dopant

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concentration. At lower concentrations of the Er3+, the optical activation of the Er3+ ions became more, which lead to the increase in the PL intensity. As the doping concentration of Er3+

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exceeded the critical concentration, the emission intensity of the (2H11/2, 4S3/2)→4I15/2 transition decreased due to concentration quenching [38, 39] and could be attributed to the distance

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between the Er3+ ions in the host lattice decreased, which may cause the pairs or clustering of the Er3+ ions lead to an increase of the cross linking resulting in the PL quenching. The

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concentration quenching effects are well reported, it depends on crystal structure, grain size,

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morphology, dopant and host materials [40, 41]. 3.5 Photometric characterization

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In order to realize the emission colour of the samples more evidently, the chromaticity coordinates of the Y2O3:Er3+ (0.1–1.0 mol%) nanophosphors were estimated using the Commission

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Internationale de l’Eclairage (CIE) 1931 system. The CIE chromaticity coordinates of the samples were considered upon a 378 nm excitation, were calculated from the emission spectra in

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the range of the 500-700 nm and is shown in Figure 4(d). The calculated colour coordinates and colour correlated temperature (CCT) are tabulated in Table 3. The chromaticity coordinates (x-y) of the PL were calculated using the standard procedure [42, 43]. The coordinates approached the green region for all the samples. With an increasing dopant concentration, the (x-y) color coordinates did not changed as shown in Figure 4 (d) and the corresponding CCT was in the 8

ACCEPTED MANUSCRIPT range of 5833.52 - 66432.60 K. The result confirmed that, all emissions increased equally proportionally with an increase in Er3+ concentration. 3.6 Thermoluminescence Figure 5(a) shows the TL glow curves of pure and Er3+ (0.1-1.0 mol %) doped Y2O3 irradiated with γ-rays for a dose of 9.0 kGy. A prominent TL glow with a maximum at 383 K along with a

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shoulder at 425 K and a weak glow maximum at 598 K were observed. With the Er3+ doping a

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prominent 385K TL glow peak intensity enhanced. It means that the Er3+ doping in the Y2O3

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phosphor was more effective to the creation of shallow traps in the phosphor. The high temperature weak peaks at 425 K and 598 K were attributed to deep traps. Vijay Singh et al.

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[44], studied gamma irradiated TL and defect centres in solution combustion synthesized Er doped Y2O3 phosphor. They reported on 20 Gy gamma rayed Y2O3:Er and shown a TL peak

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~640 K and their electron spin resonance (ESR) studies confirmed the F, F+ and V-centres present in the gamma irradiated Y2O3:Er nanophosphor [44]. In the present work, the observed

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glow peaks were attributed to the F, F+ - centre and Y2+ coordinates to O2- [45, 46]. It was found that the TL glow peak intensity for the prominent TL glow peak (383 K) increased up to 0.6

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mol% and then decreased with a further increase in dopant concentration due to the concentration quenching effect. It is clear that 0.6 mol% was an optimum concentration for the

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Er3+ ions in the Y2O3 lattice [47]. Hence, this particular Er3+ molar concentration (0.6 mol%) was used for further studies of the TL dosimeter. While its glow peak position was not perturbed as

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shown in Figure 5(b).

Figure 6(a) shows the TL glow curves of the 0.6 mol% of Er3+ doped Y2O3 nanophosphor with γ-rayed for different dose in the range of 1.0 - 13.0 kGy. The TL intensity at the glow peaks

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was plotted as a function of -dose as shown in Figure 6(b). It is observed that, the variation of TL glow peak intensity with γ-ray dose increased and it reached a maximum dose of 9.0 kGy and further decreased with increasing γ-dose. The increasing TL intensity with -doses, indicates the creation of more oxygen vacancies. Which are related to electron and hole trap centers, resulting into the recombination events that were more and lead to an increase in the TL glow peak 9

ACCEPTED MANUSCRIPT intensity [48]. The sub, linear and supra linearity dose response studies are very important to understand the dosimetry materials and it is defined as [49] F(D) =

f(D)/D f(D1 )/D1

Where f(D) and f(D1) are the TL intensity at a dose ‘D’ and ‘D1’ are the high and low doses. It was found that the region (i) was sub linearity from 1 to 2 kGy f(D) = 0.75 (<1), the region (ii)

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was linear from 5 to 7 kGy f(D) = 0.94 (~1). Hence, this behavior of the sample is useful for

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dosimetric applications. TL intensity shows sub linearity at lower does, linearity at medium dose

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and even the decrease in TL intensity of the sample at higher doses can be explained by a defect interaction model (DIM) [50]. These results indicate that the gamma dose in the range 5.0 to 7.0kGy is useful for dosimetric application. Further, the results indicate that the creations of

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defect centers increased with an increase of γ-ray dose up to 9.0 kGy thereafter decreased with a further increase of the γ-dose., This might be due to the defect concentration that was so high,

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which lead to complex/aggregated centres resulting into the quenching of the luminescence signal.

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TL glow curves analyzes are based on the glow curve deconvolution (GCD) technique.

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The calculating TL trapping parameters such as activation energy (E), order of kinetics (b) and frequency factor (s) of required isolated glow peak were obtained. The recorded TL glow curves

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of Er3+ (0.6 mol %) doped Y2O3 exposed to 9.0 kGy -irradiation seem to be complex in nature as they exhibited a broad glow. So, the broad TL glow was deconvoluted using a GCD technique

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[51, 52]. Kitis et al., reported the TL glow curve equation of general order kinetics [50], which was used for the GCD.

E T−Tm

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I(T) = Im b b/(b−1) exp (kT where, ∆=

2kT E

,

Tm

T2

E

) × [(b − 1)(1 − ∆) T2 × exp (kT .

∆m =

m

2kTm E

,

T−Tm Tm

) + Zm ] .−b/(b−1)

(1)

Zm = 1 + (b − 1)∆m

where, k is Boltzmann constant (8.6×10-5 eV K-1), β is the linear heating rate (5 Ks-1) and Im is maximum glow peak intensity and Tm is corresponding glow peak temperature. The above equation was inserted with an Microsoft Excel spreadsheet. For the fitting procedure, one has to 10

ACCEPTED MANUSCRIPT enter the initial, arbitrary but significant values for the parameters Im, Tm, E and b for each single glow peak. Soon after completion of the curve fitting, it gave the net values of Im, Tm, E and b and is shown in Figure 7. In addition, the frequency factor and figure of merit (FOM) values were found. The expression for frequency factor and figure of merit are given by [49]; −E

= s exp KT [1 + (b − 1)∆m ]

FOM =

∑ ⃒TLexp −TLthe ⃒

(3)

∑ TLthe

T

(2)

m

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βE kT2m

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Here TLexp and TLthe represent the TL intensity of experimental and theoretical glow curves respectively. FOM for the present curve fitting was 1.21 % for gamma irradiation which

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indicates that a good agreement between the theoretically fitted glow curve and the experimentally recorded TL glow curves was found. The above trap parameters are tabulated in

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Table 4. The average activation energy and frequency factor were found to be in the range of 1.16-1.47 eV and 4.93×1011 – 8.46×1014 s-1 respectively. The order of kinetics confirms that the

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deconvoluted glow peaks have obeyed second order kinetics due to the probability of retrapping centre was high.

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3.8 TL emission

TL emission is required to understand of complete TL mechanism of the material, which gives

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information on the recombination center levels in the band gap of the material. TL emission of the undoped and Er3+ doped Y2O3 nanophosphor measured for the 5.0 kGy gamma rayed

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samples is shown in Figure 8. A prominent emission peak with maxima at 545 nm and relatively weak emission with maxima at 490, 588 and 622 nm for the undoped and doped sample were

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observed at a temperature of 383 K and these emissions were due to the host related defects. Introduction of the Er3+ ions in the host, will not distort the lattice and reshuffles the structural properties. It can favor the formation of large defect centers (similar kind of host defects) in which there are strong interaction between the trapping (electron/hole) and luminescent centers resulting into a high TL signal and less fading when compared to the undoped sample. When 11

ACCEPTED MANUSCRIPT irradiated with a γ-ray, it generates electrons and holes which can trapped above and below the Fermi level within the lattice. These are preferentially trapped within the extended and distorted lattice regions. The subsequent supply of the thermal energy results in moving trapped electrons/holes to excited state and then recombination of electron-hole pair at luminescent center and resulting TL signals [13]. But incorporation of the Er3+ ion into the host does not

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glow curve of Er3+ doped Y2O3were related to host related defects.

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generate additional defects resulting in no Er3+ related emission. It confirms that the obtained TL

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3.9 Reproducibility and Fading effect

Equal quantities of the sample were also irradiated with 5.0kGy and the TL was recorded

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up to 673 K. A number of cycles of the sample and glow curve recordings were performed. The results are as shown in Figure 9 (a). No significant change in the TL intensity and glow peak

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position were observed which exhibit a very good reproducibility. The γ-irradiated samples were stored at room temperature (~27℃) for over thirty five days and the TL was taken several times

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to record the decay of the TL intensity. To study the effect of fading on the TL glow curves of the Y2O3:Er3+ (0.6 mol%), the samples were exposed for a test dose of 5.0 kGy. Figure 9 (b)

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shows the normalized TL intensity as a function of storage time after -irradiation [52]. It is observed that there was a 30% fading over a period of thirty five days. The fading was observed

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to be very high initially (a 25% decrease during the first five days) and later the fading it became slow up to twenty days thereafter the fading became saturated [49]. It indicates that fading

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depends on the band gap of the material, defects (traps) level, sample storage conditions, TL

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recording conditions etc. 4. Conclusions

Nanocrystalline Er3+ doped Y2O3 was synthesized by a low temperature sol gel technique. XRD patterns confirmed the cubic structure of the material with average crystallite size ~24-26 nm. FE-SEM micrograph of the annealed sample shows well separated spherical shape particles with average particle size ~35 nm. The energy band gap of the synthesized samples was found to be 12

ACCEPTED MANUSCRIPT 5.3 and 5.1 eV for Y2O3 and Y2O3:Er3+ (1.0 mol%) respectively. A sharp PL emission was observed in the green region under the UV excitation. The green color emission was confirmed by the CIE chromaticity color coordinates and hence, this material may be useful for applications in solid compact laser devices. γ-irradiated TL properties confirmed that the 0.6 mol% Er3+ dopant was the optimum concentration. The nanophosphors showed prominent peaks at lower temperature. It indicated that γ-ray induced a large number of shallow level trap centers. TL

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glow curves exhibited second order kinetics due to the probability of retrapping of the electrons

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which were high. TL emission of Er3+ doped Y2O3 confirmed the presence of the host related

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defects. This material showed high efficient TL, reproducibility, less fading and a prominent glow peak intensity with a linear response at the higher dose range 5.0-7.0kGy. These results

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showed that it is suitable for a high dose dosimetry application.

Acknowledgements

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The authors express their sincere thanks to Dr. S.P. Lochab, Health Physics group, Inter University Accelerator Centre, New Delhi, India for their constant encouragement and help

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during the experiment. Also, one of the author (NJS) is grateful to Inter University Accelerator

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Centre, New Delhi, for providing gamma irradiation and TL facilities. References

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[1] G. Blasse, B. C. Grabmaier, Luminescent Materials, Springer, Berlin, 1994, 65. [2] B.M. Tissue, Chem. Mater., 10 (1998)2837.

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[3] C.A.He, Y.F.Guan, L.Z. Yao, W.L. Cai, X.G.Li, Z.Yao, Mater. Res. Bull., 38 (2003) 973. [4] E. De la Rosa, L. a. Diaz-Torres, P. Salas, R. a. Rodríguez, Opt. Mater. (Amst). 27 (2005)1320.

[5] J. Hao, S. A. Studenikin, M. Cocivera, J. Lumin. 93 (2001) 313. [6] J. Hoang, R.N. Schwartz, K.L. Wang, J.P. Chang, J. Appl. Phys. 112 (2012) 023116. 13

ACCEPTED MANUSCRIPT [7] Akihiro Fukabori, Valery Chani, Jan Pejcha, Kei Kamada, Akira Yoshikawa, Takayasu Ikegami, Opt. Mater. 34 (2011) 452. [8] Numan Salah, S. P Lochab, D. Kanjilal, Jyoti Mehra, P. D Sahare, Ranju Ranjan, A.A. Rupasov, V. E. Aleynikov, J. Phys. D: Appl. Phys. 41 (2008) 085408 [9] Numan Salah, P.D. Sahare, J.Phys. D Appl. Phys. 39 (2006) 2684. [10] W. Barth, L. Dahl, J. Glatz, L. Groening, S. Richter, S. Yaramishev, Proc. European

T

Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators (Mainz,

IP

Germany) (2003) 161.

CR

[11] R. Kumar, D. Prasad, I. Prasad, J. Radiat. Res. Appl. Sci. 7 (2014) 417. [12] N.J. Shivaramu, B.N. Lakshminarasappa, K.R. Nagabhushana, Fouran Singh, J. Alloys

US

and Comp. 637 (2015) 564.

[13] S.W.S.Mckeever, Thermoluminescence of solids Cambridge University Press, 1985.

AN

[14] A.J.J. Bos, Nucl. Instr. and Meth. B 184 (2001) 3

[15] R. A. odrguez, E. De la osa, L. a. D az-Torres, P. Salas, R. Meléndrez, M. Barboza-Flores,

M

Opt. Mater. (Amst). 27 (2004) 293.

[16] E.G. Yukihara, R. Gaza, S.W.S. McKeever, C.G. Soares, Radiat. Meas. 38 (2004) 59.

ED

[17] B. Sanyal, V. Natarajan, S.P. Chawla, A. Sharma, Radiat. Meas. 45 (2010) 899. [18] T. Anh, P. Benalloul, C. Barthou, L. thiKieuGiang, N. Vu, L. Minh, J. Nanomater.(2007) 1.

PT

[19] Q. Lu, Y. Hou, A. Tang, H. Wu, F. Teng, Appl. Phys. Lett. 102 (2013) 233103. [20] Y. Mao, X. Guo, T. Tran, K.L. Wang, C.K. Shih, J.P. Chang, J. Appl. Phys. 105 (2009)

CE

094329.

[21] L. Liu, Y. Chen, X. Zhang, Z. Zhang, Y. Wang, Opt. Commun. 309 (2013) 90.

AC

[22] A.P. Milanov, K. Xu, S. Cwik, H. Parala, T. de los Arcos, H.-W. Becker, et al., Dalton Trans. 41 (2012) 13936. [23] J. Lee, Y. Tak, J. of Industrial and Engineering Chem. (1999) 5139. [24] A. Dupont, C. Parent, B. Le Garrec, J.M. Heintz, J. Solid State Chem., 171 (2003) 152. [25] B.N. Lakshminarasappa, N.J. Shivaramu, K.R. Nagabhushana, Fouran Singh, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 329 (2014)40. 14

ACCEPTED MANUSCRIPT [26] Chen Weifan, Li Fengsheng, Liu Leili, Yong xiu, J. Rare Earths, 24 (2006) 543. [27] Liu, Tong, Xu, Wen, Bai, Xue, Song, Hongwei, J. Appl. Phys. 111 (2012) 064312. [28] Xiaorui Hou, Shengming Zhou, Tingting Jia, Hui Lin, HaoTeng, J. Lumin. 131 (2011)1953. [29] James A. Dorman, Ju H. Choi, Gregory Kuzmanich, John R. Bargar, Jane P. Chang, J.Appl. Phys. 111, 083529 (2012). [30] J.Wang, H. Song, Baojun Sun, Xinguang Ren, Baojiu Chen,Wu Xu, Chemical Physics

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Letters 379 (2003) 507.

IP

[31] M. Grundmann, The Physics of Semiconductors, Springer Berlin Heidelberg, New York,

CR

2006.

[32] T.S. Atabaev, Z. Piao, Y.-H. Hwang, H.K. Kim, N.H. Hong, J. Alloys Compd. 572(2013)

US

113.

[33] A. N. Meza-Rocha, E.F. Huerta, E. Zaleta-Alejandre, Z. Rivera-Álvarez, C. Falcony,

AN

J.Lumin. 141 (2013) 173.

[34] K. Anders, A. Jusza, M. Baran, L. Lipińska, .Piramidowicz, Opt. Mater. (Amst). 34(2012)

M

1964.

[35] J.B. Gruber, G.W. Burdick, S. Chandra, D.K. Sardar, J. Appl. Phys. 108 (2010) 023109.

ED

[36] A. Tanner, C.K. Duan, Coord. Chem. Rev. 254 (2010) 3026. [37] GuifangJu, Yihua Hu, Li Chen, Xiaojuan Wang, Zhongfei Mu, Haoyi Wu, Fengwen Kang,

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J. Lumin. 132 (2012) 1853.

[38] S. Mukherjee, V. Sudarsan, R.K. Vatsa, S. V Godbole, R.M. Kadam, U.M. Bhatta, et al.,

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Nanotechnology. 19 (2008) 325704. [39] F. Thibault, D. Pelenc, B. Chambaz, M. Couchaud, J. Petit, B. Viana, Opt. Mater. (Amst).

AC

30 (2008) 1289.

[40] W.W. Zhang, W-P. Zhang, P-B. Xie, M.Y.H-T. Chen, L. Jing, Y-S. Zhang, L-R. Lou, SD.Xia, J. Colloid Interface Sci. 262 (2003) 588. [41] G. Siddaramana Gowd, M. Kumar Patra, S. Songara, A. Shukla, M. Mathew, S. Raj Vadera, et al., J. Lumin. 132(2012) 2023.

15

ACCEPTED MANUSCRIPT [42] L.L. Noto, O.M. Ntwaeaborwa, M.Y.A. Yagoub, H.C. Swart, Mater. Rese. Bult. 55(2014) 150. [43] N.J. Shivaramu, K.R. Nagabhushana, B.N. Lakshminarasappa, Fouran Singh, J. Lumin.169(2016) 627. [44] V. Singh, V.K. Rai, I. Ledoux-Rak, S. Watanabe, T.K. Gundu Rao, J.F.D. Chubaci, et al., J. Phys. D. Appl. Phys. 42 (2009) 065104. N.J. Shivaramu,

B.N.

Lakshminarasappa,

K.R.

Nagabhushana,

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[45]

Fouran

Singh,

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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 154 (2016) 220.

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[46] V.V. Osipov, A.V. Rasuleva, V.I. Solomonov, Opt. Spectrosc. 105 (2008) 524. [47] Geeta Sharm, Puja Chawla, S.P. Lochab, Nafa singh, Chalcogenide Lett. 6 (2009) 445.

US

[48] C. Pandurangappa, B.N. Lakshminarasappa, F. Singh, K.R. Nagabhushana, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms. 269 (2011)185.

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[49] C. Furetta, Handbook of Thermoluminescence, World Scientific, Singapore, 2003. [50] S. Mahajna, Y.S. Horowitz, J. Phys. D: Appl. Phys. 30 (1997) 2603.

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[51] G. Kitis, J.M. Gomez Ros and J.W.N. Tuyn, J. Phys. D. Appl. Phys. 31 (1998) 2636. [52] D. Afouxenidis, G.S. Polymeris, N.C. Tsirliganis and G. Kitis, Radiat. ProtectionDosimetry,

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149 (2012) 363.

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List of Table captions:

Table.1XRD structural parameters of annealed Er3+ doped Y2O3.

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Table.2 Refinement parameters of pure and Er3+ doped Y2O3 nanophosphor. Table.3 CIE parameters of Y2O3:Er3+ nanophosphor.

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Table.4 Trap parameters of TL glows of gamma irradiated Er3+ doped Y2O3.

List of Figure captions: Figure 1(a) XRD patterns of annealed Er3+ doped Y2O3. Figure 1(b) W-H plot of annealed Er3+ doped Y2O3. Figures 1(c) and 1(d) Rietveld refinement patterns of pure and Er3+ doped Y2O3 nanophosphor. 16

ACCEPTED MANUSCRIPT Figure 2(a) FE-SEM micrograph and Fig. 2(b): EDAX of sol-gel synthesized nanocrystalline Y2O3:Er3+ (1.0 mol%). Figure 3(a) Optical absorption of combustion synthesized Y2O3:Er3+. Figure 3(b) variation of (αE)2 with photon energy. Figure 4(a)PL excitation (λem= 563 nm) spectrum of sol gel synthesized nanocrystalline Y2O3:Er3+.

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Figure 4(c) Variation of PL intensity with dopant concentration.

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Figure 4(b) PL emission (λex=378 nm) spectra of Y2O3:Er3+ with different dopant concentration.

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Figure 4(d) Color coordinates for 378 nm excitation of PL with dopant concentration. Figure 5(a) TL glow curves of 9.0 kGy gamma irradiated nanocrystalline Y2O3: Er3+.

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Figure 5(b) Variation of with TL intensity and glow peak temperature with dopant concentration.

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Figure 6(a) TL glow curves of 1.0-13.0 kGy gamma irradiated nanocrystalline Y2O3: Er3+ (0.6 mol%).

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Figure 6(b) Variation of with TL intensity and glow peak temperature with gamma dose Y2O3: Er3+(0.6 mol%).

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Figure 7 Deconvoluted TL curve of sol gel synthesized 900 C heat treated and gamma irradiated Y2O3:Er3+.

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Figure 8 TL emission of gamma irradiated pure and Y2O3:Er3+ nanophosphor. Figure 9(a). TL Reproducibility of gamma irradiated Y2O3:Er3+.

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Figure 9(b). Effect of fading with number of days in Y2O3:Er3+ (0.6 mol%) nanophosphor.

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ACCEPTED MANUSCRIPT Table 1 Cell Volume (Å 3 )

Densit y 𝜌 (g cm-3)

Dislocation Density 𝛿 (x1015) (m2)

Inter-planar spacing at (222) (Å)

Lattice strain (%) W-H method

40.02 29.80 31.35 34.60

10.618 10.611 10.611 10.611

1195.05 1194.69 1194.82 1194.73

5.012 5.022 5.022 5.022

1.05 1.65 1.56 1.53

3.065 3.063 3.063 3.061

0.105 0.047 0.035 0.072

Table 2 2

GOF

Atoms

x

Y2O3

1.9

1.8

Y1(C3i)

0.2400

Y2(C2) O1

0.1284

a=b=c= 10.6021

0.9671

0.0091

0.2475

0.4090

0.3967

0.1475

0.3898

0.8970

Y1(C3i)

0.2399

0.2399

0.2399

0.0590

Y2(C2)

0.9666

0.0092

0.2377

0.2810

O1

0.3826

0.1732

0.3723

0.8000

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y

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0.2400

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1.3

Lattice constant (Å)

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Occupancy

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Y2O3:Er3+

z

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31.00 24.6 25.3 25.6

Lattice constant a (Å )

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Crystallite size D (nm) W-H Scherrer method

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Er3+dope d Y2O3 (mol %)

a=b=c= 10.6020

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6276.60

0.2

0.27

0.68

6432.60

0.4

0.29

0.67

6136.82

0.6

0.30

0.67

5983.60

0.8

0.31

0.67

5833.52

1.0

0.31

0.67

5833.52

Tm (K)

b

s (s-1)

402

2

1.35

435

2

1.37

2.97×1015

470

2

1.40

3.58×1014

535

2

1.42

6.44×1012

1.47

4.93×1011

3.86×1016

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1.25

600

FOM (%)

6.64×1016

382.5

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Eav (eV) 1.30

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Table4 γ-dose (9.0 kGy)

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0.68

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0.28

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CCT (K)

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Er3+ concentr ation 0.1

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1.06

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(721)

1.0 mol%

Intensity (a.u.)

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Figure 3(a)

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pure and Y2O3: Er

1) 2) 3) 4) 5) 6) 7)

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386 Sol gel synthesized Y2O3:Er

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Figure 6(b)

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Y2O3:Er

(0.6 mol%) -rayed for 9.0 kGy Experimental glow curve Deconvoluted peaks Theoretical fit

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545 383 K

5.0 kGy -irradiated Y 2 O3

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3+ Y2O3:Er (0.6 mol%)

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Figure TL emission of gamma irradiated pure and Y2O3:Er3+ nanophosphor.

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ACCEPTED MANUSCRIPT Highlights  Nanocrystalline Er3+ doped Y2O3 was synthesized by low temperature sol-gel technique.  A sharp emission is observed in the green region under the UV excitation.  TL emission peak with maxima at 545 nm and weak emission at 490, 588 and 622 nm are

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observed at 383 K temperature.  It showed high efficient TL, reproducibility, less fading and linear response at the higher dose range.  Y2O3:Er3+ nanophosphor is suitable for an high dose dosimetry application

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