Luminescence and scintillation properties of Eu2+ doped CaF2 glass ceramics for radiation spectroscopy

Journal Pre-proof Luminescence and scintillation properties of Eu radiation spectroscopy

2+

doped CaF2 glass ceramics for

M. Rahimi, M. Zahedifar, R. Azimirad, A. Faeghinia PII:

S0022-2313(19)31652-7

DOI:

https://doi.org/10.1016/j.jlumin.2020.117040

Reference:

LUMIN 117040

To appear in:

Journal of Luminescence

Received Date: 23 August 2019 Revised Date:

27 December 2019

Accepted Date: 10 January 2020

Please cite this article as: M. Rahimi, M. Zahedifar, R. Azimirad, A. Faeghinia, Luminescence and 2+ scintillation properties of Eu doped CaF2 glass ceramics for radiation spectroscopy, Journal of Luminescence (2020), doi: https://doi.org/10.1016/j.jlumin.2020.117040. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

CRediT author statement M. Rahimi: Investigation, Writing- Original draft preparation. M. Zahedifar : Methodology, Supervision, Writing- Reviewing and Editing. R. Azimirad: Supervision, Examining the scintillation properties of the glasses. A. Faeghinia: Optimization of annealing process.

Luminescence and scintillation properties of Eu2+ doped CaF2 glass ceramics for radiation spectroscopy M. Rahimi1; M. Zahedifar1, 2*; R. Azimirad3; A. Faeghinia4 1

Physics Department, University of Kashan, Kashan, I.R.Iran

2

IranInstitute of Nanoscience and Nanotechnology, University of Kashan, Kashan, I.R.Iran 3

Malek-Ashtar University of Technology, Tehran, I.R.Iran

4

Ceramic Department, Materials and Energy Research Center (MERC), P. O. Box: 31787-316, Alborz, I.R.Iran

Abstract A new scintillation material including CaF2: Eu nanocrystals contained in SiO2–Al2O3–CaO– CaF2-LiF system was successfully prepared via melting method with additional heat treatment. Structural and luminescence properties were investigated by characterization techniques including XRD, SEM, photoluminescence (PL) excitation and emission spectra and absorption profile. The emission intensity of the glass ceramics containing CaF2: Eu nanocrystals under illumination at 356 nm were significantly more than the as-made glass and enhanced with increasing the temperature and duration of the heat treatment. Spectral analysis of gamma rays showed a full-energy peak in comparison with the similar chemical compositions that do not show such a response. Also an energy continuum with specific reaction-product peak was detected for thermal neutrons. The scintillation efficiency was enhanced with increasing crystallization. The fabricated Eu-doped transparent CaF2 glass ceramics has the potential to be a desired composite scintillator for detection of low energy gamma rays and thermal neutrons. Keywords: Scintillation detector; aluminosilicate glass ceramics; Eu impurity; gamma; Neutron. * Corresponding author at: Physics department, University of Kashan, Kashan, I.R. Iran. Tel.: +98 3155912577; Fax: +98 3155912570. E-mail address: [email protected] (M. Zahedifar).

1

1. Introduction Recently, the rising interest in novel scintillation materials is increased by a promoting number of new applications in medicine diagnostics, nuclear medicine, homeland security and highenergy physics, which require go-up of material production. The most commonly used material types for radiation detection and spectroscopy applications are single crystals, transparent polycrystalline ceramics, plastics glasses, and inert gases. Each of these materials has advantages and disadvantages [1]. The traditional single crystal materials such as NaI: Tl and many other inorganic salts have several undesirable characteristics including, instability due to humidity, mechanical shock and temperature fluctuations. In contrast, one of the most promising candidates for scintillators is nanocomposite materials. The main characteristic of nanocomposite materials is stability under normal conditions, Low-cost, high-volume production possibilities and significant reaction cross sections with a wide range of nuclear radiations, including gamma rays, X-rays, alpha particles, beta particles and neutrons. Because of such advantages, nanocomposites are capable of being used as scintillating material in scintillation detectors with extensive applications [1, 2]. There are two techniques for production of nanocomposite scintillators. The first include synthesis of nanoparticles by chemical methods individually and then combining them in a polymer or epoxy matrix [3, 4]. The second is forming the nanoparticles within a glass matrix by precipitation through thermal processing (glass ceramics). In the latter technique, scintillating material is commonly made by a melt-quench process, followed by heat-treatment process. The possibility of using glass-ceramic scintillators for gamma ray spectroscopy was developed by Kang et al. [5] and Barta et al. [ 6]. 2

So far, the number of glass-ceramics form of known inorganic scintillating compositions has been limited and the scintillation performance of many of these glass-ceramics has yet to be characterized. A complete overview of this research field is available elsewhere [7]. Commercial CaF2 (Eu) crystals is a non-hygroscopic scintillator. The high strength of the CaF2 crystals is other advantage of this material. On other hand, the CaF2 compound is an ideal raw material for preparation of optical and luminescent materials due to its high transparency in a wide wavelength region (from vacuum UV to 9 µm), better matching of the refractive index (low linear and nonlinear refractive index) and low phonon energy as well [8, 9]. The known Europium-doped CaF2 scintillator was chosen by several researchers for development into glass ceramics nanocomposites. Luminescence property of transparent CaF2 glass-ceramics containing 0.1 mol% Eu

2+

ions was investigated by Fu et al. They found that the luminescence intensity of

the glass-ceramic was more than twice the base glass due to the migration of Eu2+ dopant ions into the CaF2 crystallites [10]. In 2009, Secu et al., studied a new kind of Eu doped CaF2 glassceramics and found that the photoluminescence emission located at 425 nm is due to f–d transition of Eu

2+

ions [11]. In none of these reports the scintillation properties of CaF2 (Eu)

glass ceramics were examined. Afterwards, many efforts have been devoted to investigate the scintillating properties of CaF2 (Eu) glasses ceramics [12, 13]. Recently, Struebing et al. reported 6LiF combined into Eu2+ doped CaF2 glass ceramic for thermal neutron detection. It has been demonstrated that this glass ceramics can operate as thermal neutron scintillator [14]. The glass composition of transparent glass ceramics based on CaF2 nanoparticles is critical for performance of the scintillator (especially for gamma detection) due to low density of CaF2 concentration. So, this work presentats a new kind of CaF2: Eu nanocrystal contained SiO2– 3

Al2O3–CaO–CaF2-LiF system which has been successfully prepared. Its structural and optical properties were investigated by characterizations including X-ray diffraction (XRD), SEM and photoluminescence (PL) excitation and emission spectra. The scintillation response under excitation with

137

Cs source and Am-241/Be was measured and compared to the response of

conventional NaI(Tl) single crystal scintillator.

2. Experimental procedure: 2.1. Samples preparation CaF2 nanocrystalline glass-ceramic scintillator was prepared in an aluminosilicate glass as the matrix material in the shape of a cylinder having the height of 7.24 mm and diameter of 15 mm and density of 2.7 gr/cm3. The glass-ceramics samples were manufactured by conventional meltquenching method followed by a heat treatment. High-purity SiO2–Al2O3–CaO–CaF2-LiF and EuF3 powders were completely blended together. The structure of the optimized glass ceramic scintillator was 40SiO2–20Al2O3–15CaO– 18CaF2–7LiF-0.1EuF3 in mol ratios. Firstly, 20g batches were mixed and melted in a covered alumina crucible at 1400 ºC for 2 h in an open atmosphere. The melts were quickly poured onto a preheated brass mold of 2 cm in diameter to form a transparent glass sample. Then, the sample was annealed below the glass temperature (determined from the DTA measurements) in a muffle furnace to release inner stress (550 °C for 2 h). To precipitate the CaF2: Eu nanocrystals in the glass matrix, the glass samples were subsequently heated at 760 °C for 15 min (named as GC1-2) and 760 °C for 30 min (named as GC1). The best annealing regimen for this glass composition was found to be 760ºC for 30 min in air (slightly above the CaF2 crystallization peak at about 680 ºC). 4

2.2. Samples characterization Crystalline phase of the samples was identified by X-ray diffraction (Brucker D8) using CuKα radiation. The XRD data of samples were taken in step-scan mode with step size 0.016˚ (2θ) and step time 40 sec from 20˚ to 60˚. PL spectra were recorded on a Perkin-Elmer luminescence spectrometer LS55, equipped with a Xe lamp as excitation source. UV-Visible absorption and transmittance spectra were obtained by using a Shimadzu spectrometer model UV-1800. The microstructure analysis of the samples was carried out by scanning electron microscopy (FESEM (MIRA3 TESCAN) equipped with an energy dispersive spectroscopy apparatus (EDS) at operating voltage of 15 kV. Prior to the FESEM observation, glass-ceramics were polished and chemically etched by immersion in 0.5 vol% HF solution for 10s. Gamma pulse-height spectra measurements were conducted using a

137

Cs disk source with the

photon energy of 662 keV and an Am- Be source encapsulated in welded stainless steel. Since, an Am-Be source produces neutrons in broad energy range; a polyethylene cylinder was used to thermalize the fast neutrons. For Gamma ray and neutron radiation measurements, first optical grease was used between one side of the sample and a photomultiplier tube (PMT, model R1828 from Hamamatsu) to hamper interface scattering. After that, source was located in contact with other side of the sample. Photons coming out of the nanocomposite samples were integrated with a NIM modules set-up consist of an IAP 8100 high voltage power supply, IAP 3001 preamplifier, IAP 3600 amplifier and an IAP 4110 ADC-multichannel analyzer.

3. Results and discussion 3.1 XRD and SEM results

5

XRD analysis was conducted in order to explore crystalline phases of glass-ceramics. The XRD patterns of CaF2 oxyfluoride glass–ceramics doped with 0.1 mol% Eu is shown in Fig. 1(a). As is evident in this figure, no diffraction peaks (only one broad peak) are there in the as-quenched glass, an indication that the glass is completely amorphous without crystallization peaks. After heat-treatment at 760ºC for 15 min (GC1-2), one sharp peak was appeared on the broad peak in the glass– ceramics that probably is due to small crystallite size and low crystalline ratio. On the other hand, it is expected that CaF2 to be crystallized at 760°C. With increasing the annealing time from 15 to 30 min, several sharp diffraction peaks were easily identified. These peaks are ascribed to precipitated CaF2 nanocrystals in the glass matrix. The glass-ceramic samples retained high transparency after annealing at 15 and 30 min, but with increasing the annealing time, sample appeared cloudy as a consequence of increased light scattering from CaF2 nanocrystals. The line positions agree with those predicted for the cubic CaF2 (reference # 01-070-1469 in the ICSD database) and indexed as (1 1 1), (2 2 0), and (3 1 1). From the obtained peak width of XRD pattern, the crystallite size in the glass–ceramics can be determined by the Scherrer’s equation: D=

kλ ω cos θ

(1)

where D is the crystallite size, λ the wavelength of X-ray (Cu Kα: 1.541Å), θ the angle of diffraction, ω the full width at half maximum (FWHM) of the diffraction peak, and constant K= 0.89.

6

The Scherrer equation is applied to the (2 2 0) reflection of cubic CaF2 at about 47.11. All line profiles are fitted by a Lorentzian function, as presented in Fig. 1(b). The analysis of the XRD pattern revealed an increase of the lattice constant d from 5.450 to 5.467 Å. Also it was found that the crystallite size of CaF2 nanocrystalline precipitates increases monotonically from about 28 to 47nm with increasing annealing time. To study the microstructural features and particle distribution in the glass-ceramic matrix, the samples were analyzed with field emission scanning electron microscopy in different magnifications. FESEM micrograph of glass-ceramic sample heat-treated at 760°C for 15(GC1-2) and 30(GC1) minutes are shown in Figs.2 (a-b-c-d-e-f) after HF solution treatment. In Fig. 2, a uniform and homogeneous distribution of spheroid dark grey crystals are observed that are extensively dispersed in the microstructure as the dominant crystalline phase. According to the XRD patterns of Fig. 1(b), the observed crystals can be assigned to CaF2 nanoparticles. These particles include agglomerated nano grains with the size of 30–50 nm. A slight difference can be identified between the heat treated sample at 760 ºC for 15 and 30 min. By increasing the annealing time, the grain size rises gradually that is illustrated in Fig. 2(d-e-f). Observed size in the SEM images in Fig. 2 is approximately in accordance to the XRD results. 3.2 Optical properties Rare earth elements in glasses and glass ceramics have critical optical properties as well, from controlling refractive index and dispersion to more active roles in photonic devices. Among different rare earth elements (RE), europium is one of the effective materials which is commonly used as rare earth activator in development of optically active materials. 7

Europium ions can exist in both Eu2+ and Eu3+ forms of oxidation states, depending on the host material or environment when the material is synthesized. The Eu2+ emissions are usually composed of broad bands corresponding to the 4f6 5d-4f7 transitions. It is the only lanthanide ion with the ground state angular momentum of J=0, so exceptional restrictions exist on the induced electric-dipole transitions originating from the ground state. On the other hand, Eu3+ ions emit distinct narrow lines assigned to the 5D0-7FJ transitions (J =0-6) [15, 16]. Figure 3-i (a), (b) and (c) respectively shows the emission spectra at room temperature for asmade glass along with the heat‐treated glass ceramics for 15 and 30 min by exciting at 367 nm. As is observed, the luminescence of the as-made glass is very weak, and increases with heat‐treatment at higher temperatures. Luminescence enhancement in glass ceramic sample over the precursor glass sample can be illustrated considering that the density of the glass sample is lower than the corresponding crystalline matrix, so in the crystallization process, the variation in relative crystal field, crucially affects the luminescence output of the impurity ions. The emission intensity of the annealed samples comes to be stronger with increasing the annealing time from 15 min to 30 min. While the emission spectrum of the sample undergone longer annealing time is more intense, the spectra show similar features for different annealing times. The strong increment in the emission intensity is recognized by means of more formation of Eu2+ leading to stronger luminescence. PL and PLE spectra of the glass ceramic sample with 0.1% Eu doping are also shown in Figure 3(ii). A broad emission band peak is observed following excitation at 356 nm. The PLE spectrum shows a distinct excitation peak at 356 nm which was measured with monitoring the wavelength at 425 nm. These results are approximately similar 8

to those reported by Fu et al. and Struebing et al. [10, 14]. They found that CaF2: Eu glass ceramic in presence and absence of 6Li have emission peaks about ∼420nm and 428nm, upon exciting the sample with 335 and 367nm wavelengths respectively. They reported that the excitation and emission bands are due to the optical transition from 4f-5d band of Eu+2 ions doped in the CaF2 glass-ceramic. Shulgin et al. reported that the emission peak from CaF2: Eu single crystal is located at 433 nm [17]. The Blue-shifting of light emitted at 420 nm in this sample is attributed to the increased band gap, i.e. when the particle size decreases, the effective band gap increases. Therefore, the emitted photon has comparatively higher energy giving photoluminescence peak at shorter wavelength. The broader peak is due to different sizes of nanoparticles in material and also is susceptible to the crystal field. The excitation and emission bands have a Stokes shift of 51 nm and slight overlap caused by relatively weak self-absorption. An absorption spectrum was also included in Figure 3(ii) which is consistent with the PLE results. Figure 4 shows the transmittance and absorption spectra of the samples from 220-800 nm which displays absorption bands in the range of 220–360 nm. This is likely due to transitions of 5d-4f bands in Eu+2 ions. As seen in Figure 4, an improvement in transmittance attains with increasing the annealing time which could be attributed to uniform distribution of CaF2 nanoparticles and dopant material or smaller grain size in the prepared glass ceramics. 3.3 Radiation measurement

9

Gamma-ray spectroscopy pulse heights for three samples are presented in Figure 5. As is observed, the untreated glass sample (Glass) has no well-defied photo-peak under gamma ray excitation. The photoelectric effect in which the incident photon energy is completely absorbed in the scintillation material is responsible for creating the photopeak. After annealing at 760°C for 15 min (GC1-2) to create nanophosphor-embedded glass-ceramic scintillator, the light yield was significantly improved with remarkable enhancement in light pulse height. The first photopeak was obtained at channel #128 corresponding to 662 keV γ-rays from

137

Cs source as measured

with annealed glass ceramic sample at 760°C for 15 min. This photopeak is well-separated from the Compton continuum in the pulse height spectrum. Also, a relatively intense photopeak clearly observed at channel #178 (137Cs spectrum) for the annealed glass ceramic sample at 760°C for 30 min (GC1). It is noted that the sample with longer annealing time exhibits a better resolved photopeak. This peak is formed as a result of suitable nanoparticle loading and uniform distribution of nanoparticles in the glass matrix and suitable thickness (7mm) of the glass ceramic. The relative resolution is defined as the full-width at half-maximum energy divided by the incident energy. The findings showed that the GC1 sample have superior resolution of about 21% versus almost 25% for the GC1-2 sample. These results can be compared with 8% resolution of NaI: Tl single crystal scintillator. Also the light yield of the sample GC1 to that of NaI scintillation detector (GC1/NaI) was measured to be 0.2 and the ratio GC1-2/NaI was 0.1. Relatively low yield of the produced glass ceramic sample can be attributed to the small particle size, the high surface area and imperfections existing on the surface of CaF2 nanoparticles which considerably reduces the light yield. Substantial increase in the light yield can be achieved by increasing the particle size and preserving the transparency of the glass ceramics. 10

The results on the resolution of the prepared samples are improved compared to the other reports on scintillation of nanocrystalline CaF2: Eu glass ceramic [14, 18], but the resolution can still be upgraded. The observed resolution is poor compared with that of NaI: Tl single crystal. This firstly may be ascribed to the low number of CaF2 crystallites in the glass matrix. Secondly, some impurity ions might not be entirely eliminated in the melting process, causing reduction in the light yield of the sample. Finally, the increase in CaF2 crystallite size, transmission and thickness of the ceramics is likely to improve the light yield. By combining 6LiF into the glass matrix, the glass ceramic sample can detect thermal neutrons because of high thermal neutron absorption cross section of 6

Li. Figure 6 shows the pulse-height of CaF2: Eu2+ glass ceramic samples irradiated by a

241

Am-

Be neutron source in presence and absence of polyethylene. A small neutron induced photopeak around channel number 225 was observed in pulse-height profile of the annealed glass ceramic sample at 760°C for 15 min (GC1-2). No distinct peak was observed without polyethylene in the pulse-height spectrum. This result suggests that the peak was created by thermal neutrons excitation. By increasing the annealing time from 15 to 30 min, the light yield was further improved and a distinctive neutron induced photopeak is observed (at channel number 510). Considering the weight percent of CaF2 in the glass matrix (about 20%) and the dimensions of the cylindrical glass matrix (diameter of 1.5 cm and the height of 0.72 cm) and the weight of 33.4 gm, the average size of nanoparticles (about 40 nm) and the lattice constant of CaF2, the distance between neighboring grains was estimated to be about 0.03 micron which is much less than the range of alpha and tritons created by neutron absorbed in 6Li.

Conclusion

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A new scintillation material including CaF2: Eu nanocrystal contained in SiO2–Al2O3–CaO– CaF2-LiF system was successfully prepared through melting method with additional heat treatment. Spectral analysis of nuclear radiation revealed a distinctive photopeak corresponding to 662 keV γ-rays from

137

Cs source which has not been reported so far. Therefore, CaF2: Eu2+

glass ceramic gamma and neutron scintillator can be a promising material, particularly by further improvement of the efficiency. Considering the transparency as an important property of scintillators, in order to maintain transparency of the composite scintillator, the refractive index of composite should match with CaF2 refractive index (about 1.44 at 500 nm). This can be achieved by optimizing the content of CaF2 and CaO in the glass ceramic matrix, varying the fraction of components in the glass matrix or introducing other components in the glass matrix to minimize light scattering and acquire high transparency of the composites, leading to enhancement in light yield of CaF2: Eu+2 glass ceramic. Acknowledgement The authors are grateful to research council of the University of Kashan for providing financial support to undertake this work (Grant number 785216).

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[3] T. Rogers, C. Han, B. Wagner, J. Nadler, Z. Kang, Synthesis of luminescent nanoparticle embedded polymer nanocomposites for scintillation applications, MRS Online Proceedings Library Archive, (2011) 1312. [4] Z. Kang, Y. Zhang, H. Menkara, B. K. Wagner, C. J. Summers, W. Lawrence, V. Nagarkar, CdTe quantum dots and polymer nanocomposites for x-ray scintillation and imaging, Applied physics letters 98(18) (2011) 181914. [5] Z. T. Kang, R. Rosson, B. Barta, C. Han, J. H. Nadler, M. Dorn, GdBr3: Ce in glass matrix as nuclear spectroscopy detector, Radiation Measurements 48 (2013) 7-11. [6] M. B. Barta, J. H. Nadler, Z. Kang, B. K. Wagner, R. Rosson, Effect of host glass matrix on structural and optical behavior of glass–ceramic nanocomposite scintillators, Optical Materials 36(2) (2013) 287-293. [7] D. de Faoite, L. Hanlon, O. Roberts, A. Ulyanov, S. McBreen, I. Tobin, Development of glass-ceramic scintillators for gamma-ray astronomy, In Journal of Physics: Conference Series (IOP Publishing) 620(1) (2015) 012002. [8] J.L. Doualan, P. Camy, R. Moncorgé, E. Daran, M. Couchaud, B. Ferrand, Latest developments of bulks crystals and thin films of rare-earth doped CaF2 for laser applications, Journal of Fluorine Chemistry 128 (2007) 459–464. [9] A. Lyberis, G. Patriarche, P. Gredin, D. Vivien, M. Mortier, Origin of light scattering in ytterbium doped calcium fluoride transparent ceramic for high power lasers, Journal of the European Ceramic Society 31(2011) 1619–1630. [10] J. Fu, J. M. Parker, P. S. Flower, R. M. Brown, Eu2+ ions and CaF2-containing transparent glass-ceramics, Materials research bulletin 37(11) (2002) 1843-1849. [11] M. Secu, C. E. Secu, S. Polosan, G. Aldica, C. Ghica, Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics, Journal of Non-Crystalline Solids 355(37-42) (2009) 1869-1872. [12] W. Deng, J. S. Cheng, New transparent glass–ceramics containing large grain Eu3+: CaF2 nanocrystals, Materials Letters 73 (2012) 112-114. [13] M. Secu, C. E. Secu, C. Ghica, Eu3+-doped CaF2 nanocrystals in sol–gel derived glass– ceramics, Optical Materials 33(4) (2011) 613-617. 13

[14] C. Struebing, J. Chong, G. Lee, M. Zavala, A. Erickson, Y. Ding, a neutron scintillator based on transparent nanocrystalline CaF2: Eu glass ceramic, Applied Physics Letters 108(15) (2016) 153106. [15] Z. Lian, J. Wang, Y. Lv, S. Wang, Q. Su, the reduction of Eu3+ to Eu2+ in air and luminescence properties of Eu2+ activated ZnO–B2O3–P2O5 glasses, Journal of alloys and compounds 430 (1-2) (2007) 257-261. [16] K. Biswas, A. D. Sontakke, R. Sen, K. Annapurna, Luminescence properties of dual valence Eu doped nano-crystalline BaF2 embedded glass-ceramics and observation of Eu +2→ Eu+3 energy transfer, Journal of fluorescence 22(2) (2012) 745-752. [17] B. V. Shul'gin, S. I. Buzmakova, L. V. Viktorov, A. L. Krymov, A. L. V.L., Petrov, S.V. Podurovskii, A.A. Kozlov, B.M. Shapiro, M.Y. Shrom, A.I. Nepomnyashchikh and P.V.Figura, Scintillation detectors working with CaF2-Eu single crystals, Atomic Energy 75(1) (1993)534538. [18] J. Fu, M. Kobayashi, S. Sugimoto, J. M. Parker, Scintillation from Eu+2 in nanocrystallized glass, Journal of the American Ceramic Society 92(9) (2009) 2119-2121. Figure Captions Fig.1. (a) XRD spectra of the as prepared glass and glass ceramics at 760° C for different times and (b) the XRD peak used for particle size analysis of glass ceramic sample and the corresponding Lorentzian fitting curve. Fig.2. SEM micrograph of polished and chemically etched glass after heat treated at 760°C for 15min at different magnifications: (a) 50000 (b) 100000 (c) 135,000. Heat treated at 760°C for 30 min at different magnifications: (d) 50000 (e) 100000 (f) 135,000 Fig.3. (i) PL spectra of samples for different heat treatments. The emission spectrum of the untreated sample is also included. (ii) Normalized PL (dashed and dotted), and PLE (dotted), spectra of Eu+2 doped CaF2 glass-ceramic sample annealed at 760°C for 30 min together with the absorption spectra. Fig.4. Transmittance spectra of Eu+2: CaF2 glass ceramics. The inset of the figure illustrates the absorption spectra.

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Fig. 5.a) Pulse height spectra of CaF2: Eu glass ceramics scintillator under gamma irradiation for untreated, GC1 and GC1-2 samples. The

137

Cs gamma ray spectrum from NaI:TI detector and

CaF2: Eu glass ceramics are also shown in the inset for comparison. Fig. 6. Neutron spectra of 6LiF-contained CaF2: Eu glass ceramics samples irradiated with 241

Am-Be neutrons with and without polyethylene. The spectra of the samples annealed at 760°C

for 15min in presence and absence of polyethylene are shown in the inset.

15

a

d

b

e

c

f

1500

untreated GC1-2 GC1

Counts

1200

Counts

4500

900

NaI(Tl) GC1-2 GC1

3000 1500 0

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400

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Channel number

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Eu doped CaF2 transparent glass ceramics were prepared by melt-quenching method with subsequent heat treatment.
Optical and scintillation properties of CaF2 glass ceramics was characterized.
The scintillation response of CaF2 glass ceramics were better than those of the glass ceramics of the similar compositions.
Present compositions of CaF2 glass ceramics have the potential of a novel nanocomposite scintillator.

Declaration of interests
☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: