Ce3+ doped glass for radiation detection material

Author’s Accepted Manuscript Ce3+ doped glass for radiation detection material N. Wantana, E. Kaewnuam, N. Chanthima, S. Kaewjaeng, H.J. Kim, J. Kaewkhao

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S0272-8842(18)32181-3 https://doi.org/10.1016/j.ceramint.2018.08.121 CERI19156

To appear in: Ceramics International Cite this article as: N. Wantana, E. Kaewnuam, N. Chanthima, S. Kaewjaeng, H.J. Kim and J. Kaewkhao, Ce3+ doped glass for radiation detection material, Ceramics International, https://doi.org/10.1016/j.ceramint.2018.08.121 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. 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.

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Ce3+ doped glass for radiation detection material N. Wantanaa,b, E. Kaewnuamc, N. Chanthimaa,b , S. Kaewjaengd, H.J. Kime and J. Kaewkhaoa,b* a

Physics Program, Faculty of Science and Technology, Nakhon Pathom Rajabhat University, Nakhon Pathom, 73000, Thailand b Center of Excellence in Glass Technology and Materials Science (CEGM), Nakhon Pathom Rajabhat University, Nakhon Pathom, 73000, Thailand c Physics Program, Faculty of Science and Technology, Muban Chombueng Rajabhat University, Ratchaburi, 70150, Thailand d Department of Radiologic Technology, Faculty of Associated Medical Sciences, Chiang Mai University, Chiang Mai, 50200, Thailand e Department of Physics, Kyungpook National University, Daegu, 702-701, Republic of Korea

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Abstract The Ce3+ doped sodium-gadolinium-aluminum-phosphate glasses, with 20Na2O−10Gd2O3−10Al2O3−(60-x)P2O5− xCeF3 (where x = 0.00, 0.10, 0.50, 1.50, 2.00 and 3.00 mol%) composition, have been measured and analyzed. The prepared glasses were studied various properties such as physical, optical, luminescence and scintillation. The densities of glasses were found to increase with the concentration of CeF3 while molar volumes decreased. The value of absorption edge is shifted from 313 nm of host glass to longer wavelength with CeF3 doping. The indirect and direct band gap decreased with increasing CeF3 content which corresponded to the molar volume reduction representing the enhancement of non-bridging oxygen (NBO) number in glass network. Photoluminescence spectra showed the strong emission bands centered between 325 – 347 nm under Ce3+ directly excitation and Gd3+ excitation. The optimum concentrations of CeF3 concentration in this glass is 2.00 mol% as it resulted the maximum emission intensity. The strongest emission band of x-ray induced optical luminescence is around 375 nm. The integrated scintillation efficiency of 2.0 mol% CeF3 doped glass was 9.6% compared with bismuth germanium oxide (BGO) crystal. The most dominant decay times of 2.0 mol% doped glass was fast as 26.8 ns that performed the rapid response with coming excitation energy. In this work, our developed glasses performed the strong and fast luminescence signal which can be applied as the scintillation material in radiation detector. Keywords: Scintillation glass; Cerium; Luminescence

________________________________________________________________________________________________ 1. Introduction The scintillation glasses possess the advantages of simple preparation, low cost, multi-component homogeneous doping, various size and shape, several form such as fiber and bulk for the scintillating detection of x-ray and γ ray or neutrons [1-5]. Phosphate glasses are the suitable host for glass scintillator because their structure performs a strong dispersing ability to rare-earth ions, high luminescence efficiency of rare earth ions dopant, good mechanical properties, high ultraviolet (UV) /visible light (VIS) transmittance, low darkening effect, then, there is low melting temperature [1,67]. The Cerium ions (Ce3+) were widely used as the activators in various fluoride and oxide materials. Spectroscopic properties of Ce3+-doped crystals and glasses have been very promising due to its high light yield and short luminescence decay time [4,5]. Ce3+ ions (4f1 electron configuration) show the efficient luminescence in the UV – VIS spectral region with broad band emission due to allowed 5d−4f transitions [4,8]. The wavelength position of the 5d−4f transitions depends strongly on the nature and structure of host through the crystal-field splitting of the 5d configuration and widely varies from near UV to red light region. The decay time of the Ce3+ emission is very short (10-8−10-9 s), due to parity and spin-allowed 5d−4f transitions, which good response for scintillation devices [5]. For previous work about Ce3+ doped *

Corresponding author. Tel.: +66819218716; Fax.:+6634261065 E-mail address: [email protected] (Jakrapong Kaewkhao) Pages provided by publisher

N. Wantana et al. phosphate-based glass, Othman and co-workers prepared Ce3+/Sm3+ doped lithium-alkaline earth- alumino-phosphate glasses with high density and performs the high potential of luminescence properties for WLED [9]. Park and colleagues were study the Ce3+ doped gadolinium-calcium-silicaborate glasses and obtained good luminescence properties for scintillating application in high energy and nuclear physics, radiation monitoring and homeland security [4]. Yao and team investigate luminescence properties and compared scintillation efficiency of Ce3+ doped barium gadolinium aluminum fluorophosphates glasses with bismuth germanium oxide (BGO) crystal, theses glasses luminescence decay time were short as in 25 - 35 ns and they possessed 25% efficiency of BGO [7]. From literatures, Ce3+ doped sodiumgadolinium-aluminium-phosphate glass has never been discovered and researched. High radiation capture ability and energy transfer of gadolinium ion (Gd3+), strong and fast luminescence properties of Ce3+ and good physical properties of lithium aluminum phosphate glass, all of these possibly give a new route for development in the scintillating material applications. This paper reports about the study of the Ce3+ doped sodium-gadolinium-aluminum-phosphate glasses (NaGdAlPCe). Physical, optical and luminescence properties were investigated as a function of CeF3 concentration. The scintillation potential of glasses were analyzed by x-ray induced optical luminescence and compared with BGO crystal. 2.

Experimental

The NaGdAlP-Ce glasses under 20Na2O−10Gd2O3 −10Al2O3−(60-x)P2O5−xCeF3 system (x = 0.00, 0.10, 0.50, 1.50, 2.00 and 3.00 mol%), were prepared by the melt-quenching technique using high-purity chemicals of Na2CO3, Gd2O3, Al2O3, NH4H2PO4 and CeF3. Total 20 g of the batch composition was thoroughly crushed in an agate mortar. The homogeneous mixtures were taken in the alumina crucibles and melted in an electric furnace at 1200 °C for 1 h. Then, melt samples were poured onto a pre-heated graphite mold and subsequently annealed at 500 °C for 3 h in furnace to remove the thermal strain. Finally, all glasses were left to room temperature and taken to cut and polished in dimension of 1.0 x 1.5 x 0.3 cm3. The densities of the glasses were determined by Archimedes´ method using water as the immersion liquid, which were brought to calculate the molar volume of glasses. Absorption spectra were recorded by using ultraviolet–visible light – near infrared (UV–VIS–NIR) spectrophotometer (Shimadzu, 3600). Optical band gaps were calculated for direct and indirect transitions from the absorption spectra of each sample. The photoluminescence spectra were then monitored at room temperature with a spectrofluorophotometer (Cary-Eclipse) with xenon light source. The glass samples were also investigated for x-ray induced optical luminescence, based on the specially designed instrumental setup in our research lab, as shown the diagram in Fig. 1. This setup consists of the Cu target x-ray generator (Inel, XRG3D-E), whose x-ray source was operated at 50 kV and 30 mA, and the spectrometer (QE65 Pro, Ocean Optics) with an optical fiber to detect the emission spectra. Luminescence decay curve of glasses were studied by using the DeltaproTM fluorescence life time system (HORIIBA scientific) with 286 nm DeltaDiode light source (DD-290) and picosecond photon detector (PPD-850).

Fig. 1 Schematic diagram of the experiment setup for x-ray induced optical luminescence

3. Results and discussion All NaGdAlP-Ce glasses prepared in this work are shown in Fig. 2, which perform the colorless and high transparent bulk.

Fig. 2 The NaGdAlP-Ce glasses.

The determined densities and molar volumes of glasses are shown in Fig. 3. Since CeF3 possesses higher density (6.16 g/cm3) and it was doped into glass by replacing of P2O5 (2.39 g/cm3), the total glass density increased with increasing of CeF3 concentration. The high density, short radiation length of the scintillator are particularly important in applications such as high energy experiments and medical imaging [10]. The density of NaGdAlP-Ce glasse was in a range of 3.015 - 3.126 g/cm3. The molar volume tended to decrease with increment of CeF3 contents. Previously, Choi and Rye could prove and explain that CeO2 doping made non-bridging oxygen (NBO) formed and changed phosphate unit structure from Q2 to Q1. This created a cross-linked of phosphate glass network leading to the structural contraction and glass molar volume reduction [8]. Therefore, it is possible to said that CeF3 doping could also add the number of NBO in NaGdAlP glass network. 3.14

48.0 Density Molar volume

3.12

47.8

3

47.2 3.06

47.0

3.04

46.8

3.02 3.00

46.6 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3

Density (g/cm )

47.4

3.08

Molar volume (cm /mol)

47.6

3.10

46.4

Concentration of CeF3 (mol%)

Fig. glasses.

3

The

densities

and

molar

volumes

of

NaGdAlP-Ce

Absorbance (arb. units)

2.0 3.00Ce

1.5

2.00Ce

1.0

1.50Ce

0.5

0.50Ce 0.10Ce 0.00Ce

0.0 200

300

400

500

600

700

800

Wavelength (nm)

Fig. 4 The absorption spectra of NaGdAlP-Ce glasses.

The study of optical absorption edge is a useful information for understanding the optically induced transitions and optical band gaps of materials. The principle of the technique is that a photon with energy greater than the band gap energy will be absorbed. There are two kinds of optical transitions at the fundamental absorption edge: direct and indirect transitions,

N. Wantana et al. both of which involve the interaction of an electromagnetic wave with an electron in the valence band [11]. Fig. 4 shows the absorption spectra of the NaGdAlP-Ce glasses recorded at room temperature in the wavelength region 200–800 nm. Glasses absorbed photons in UV and blue light region which perform the cut-off wavelength around UV/VIS junction. From table 1, it is clear that the cut-off wavelength observed at 313 nm for undoped glass is found to be shifted to longer wavelength side (red shifted) with increasing of CeF3 concentration (317 to 362 nm for 0.10 to 3.00 mol% of CeF3). Table 1. Cut-off wavelength, indirect and direct band gap of the NaGdAlP-Ce glasses. CeF3 concentration (mol%) 0.00 0.10 0.50 1.50 2.00 3.00

6

Cut-off wavelength (nm) 313 317 323 329 342 362

Indirect band gap (eV) 3.297 3.269 3.248 3.212 1.284 0.244

Direct band gap (eV) 3.485 3.470 3.450 3.419 3.171 2.155

3.30

(a)

4

3.28 3.27 3.26 3.25 3.24 3.23 3.22 3.21

0.0

0.5

1.0

1.5

Concentration of CeF3 (mol%)



h cm



1/2

eV )

5

Indirect band gap (eV)

3.29

3

0.00Ce 0.10Ce 0.50Ce 1.50Ce

2 3.0

3.2

3.4

3.6

3.8

4.0

h (eV) 1000

(b)

3.49 3.48

1/2

eV )



h cm



600

Direct band gap (eV)

3.47

800

3.46 3.45 3.44 3.43 3.42 3.41

400

0.0

0.5

1.0

1.5

Concentration of CeF 3 (mol%)

0.00Ce 0.10Ce 0.50Ce 1.50Ce

200

0 3.2

3.4

3.6

3.8

4.0

h (eV)

Fig. 5 (a) Indirect band gap and (b) direct band gap of the NaGdAlP-Ce glasses.

The optical band gap (Eg) of glass was calculated using the equation; (1)  h  B( h  Eg )n ,

Where  is the absorption coefficient, h is the incident photon energy, B is a constant, and n value can be 2, 3, 1/2 and 1/3 for indirect allowed, indirect forbidden, direct allowed and direct forbidden transitions, respectively [8,11-12]. In this glass systems, the above equation depicted a straight line for indirect allowed (n = 2) and direct allowed transition (n = 1/2). The calculated value for both indirect and direct band gap of glasses are presented in table 1 and Fig. 5. The indirect and direct band gap energy decreased with increasing of CeF3 concentration from 3.297 to 0.244 eV and 3.419 to 2.155 eV, respectively. The reduction of the optical band gap, after doping of CeF3 is attributed to the structural changes with NBO in the glass network [8,11]. Since NBO bounded an excited electron less tightly than bridging oxygen (BO) [13], it can be discussed about the optical gap and cut-off wavelength in 2 ways. First, the increment of NBO towards CeF3 concentration increased the donor center in glass matrix resulting to narrow down of the optical band gap [8,12]. Second, the increment of NBO made a lot of negative charges surrounding Ce3+ which induced the 4f shell of Ce3+ get closer to 5d shell which shifted the 4f-5d transition energy to lower energy side and increased the cut-off wavelength in the absorption spectra [13]. Fig. 6 (a) shows the excitation and emission spectra of the NaGdAlP-Ce glasses. The Ce-doped glass samples exhibited the emission bands centered between 342 to 347 nm under directly excitation wavelengths of Ce3+ across 308 nm, corresponding to the 5d – 4f transition of Ce3+ [4]. For the excitation bands of 347 nm emission wavelength, they centered among 304 to 315 nm. Moreover, Gd3+ excitation at 275 nm (8S7/2→6IJ) were also applied for Gd3+-Ce3+ energy transfer study, obtained emission bands centered between 325 – 343 nm. The red shift of those emission and excitation bands with CeF3 increment possibly corresponded to the effect of NBO in glass network as mentioned above. The emission intensity increased with increasing of Ce3+ concentration from 0.10 to 2.0 mol% and then decrease because of concentration quenching effect. Moreover, the emission intensity under Ce3+ directly excitation (308 nm) were higher than ones under Gd3+ excitation (275 nm). All process of luminescence transitions under Ce3+ directly and Gd3+ excitation are shown in Fig. 7. 900 800

3+

Ce direct excitation



EM

= 347 nm

Excitation

700

Intensity (a.u.)



(a)

= 308 nm EX

Emission

342-347 nm

304-315 nm

600 0.00Ce 0.10Ce 0.50Ce 1.50Ce 2.00Ce 3.00Ce

500 400 300 200 100 0

250

300

350

400

Wavelength (nm)

450

N. Wantana et al. 900

3+

Gd excitation

(b)

800

0.00Ce 0.10Ce 0.50Ce 1.50Ce 2.00Ce 3.00Ce

Emission

325-343 nm

Intensity (arb. units)

700 600



500

= 275 nm

EX

400 300 200 100 0

300

350

400

450

Wavelength (nm) Fig. 6 (a) The excitation (dash line) and emission (solid line) spectra under Ce3+ directly excitation and (b) The emission spectra under Gd3+ excitation of the NaGdAlP-Ce glasses.

From x-ray induced optical luminescence spectra in Fig. 8, the strong emission bands center around 375 nm wavelength (5d – 4f transition of Ce3+) and the highest intensity of emission is belonged to 2.00 mol% Ce3+ doped glass due to concentration quenching similar with the photoluminescence spectra. The NaGdAlP-Ce glass doped with 2.00 mol% of CeF3 and BGO were analyzed scintillation comparatively via the x-ray luminescence spectrum as show in Fig. 9. Under the same experimental conditions, the band total area centered at 375 nm of NaGdAlP-Ce glass and the band total area centered at 520 nm of BGO crystal were evaluate to compared the integral scintillation efficiency. From result, the integral scintillation efficiency of NaGdAlP-Ce glass is about 9.6% of the BGO crystal. 40 6

IJ

35

6

P7/2

5d-4f

15

325 - 347 nm

20

EX= 308 nm

25

EX=275 nm

3

-1

Energy (10 cm )

30

Energy transfer

10 5 2 8

S7/2

0

Ce3+

Gd3+

Fig. 7. Energy the NaGdAlP-Ce glasses.

level

diagram

F7/2 F5/2

2

of

Gd3+

and

Ce3+

ions

in

120 120

375 nm

110

100

Intensity (arb. units)

100

Intensity (arb. units)

90 80 70

80 60

40

20

60

0

50

0

1

2

3

Concentration of CeF3 (mol%)

40

0.00Ce 0.10Ce 0.50Ce 1.50Ce 2.00Ce 3.00Ce

30 20 10 0 350

400

450

500

Wavelength (nm) Fig. 8. The x-rays induced optical luminescence spectra of the NaGdAlP-Ce glasses.

The luminescence decay curve of CeF3 doped NaGdAlP glasses UV excitation with 286 nm are shown in Fig. 10. All curves performed the corresponding behavior to the three-component exponential decay and they were fitted with this expression to obtain the lifetime as shown in inset table of Fig. 10. All decays of CeF3 doped glasses were dominated by the fast decay component (66 - 75 %). There was the ultrafast decay component (3 and 4 %) in 0.10 and 0.50 mol% doped glasses, while the intermediate decay component (10 and 11 %) were found in 1.50 and 2.00 mol% doped ones. The most dominant fast decay times of each glass typically represents to the duration of Ce3+ 5d-4f transition [14,15] and they varied between 17.3 - 29.4 ns. These values increased with increment of CeF3 concentration from 0.10 to 1.50 mol%, for over than 1.50 mol%, it decreased possibly due to the concentration quenching effect. The most dominant decay time of 2.00 mol% doped glass is 26.8 ns. 200

BGO 2.00Ce

520 nm

180

140 120

375 nm

Intensity (arb. units)

160

100 80 60 40 20 0

400

500

600

700

800

900

Wavelength (nm) Fig. 9. The x-rays induced optical luminescence spectra of the 2.00 mol% CeF3 doped NaGdAlP glass, compared with BGO scintillator.

N. Wantana et al.

Fig. 10. The typical luminescence decay curve under 286 nm excitation of NaGdAlP-Ce glasses doped with 0.10 and 2.00 mol% of CeF3

4. Conclusion The densities / molar volumes of the NaGdAlP-Ce glasses increased / decreased with increment of CeF3 concentration. Molar volume reduction possibly represented the enhancement of NBO number in glass network. Glass absorbed photons in UV and VIS region and cut-off wavelength increase with increasing CeF3 concentration to longer side (red shift). The indirect and direct band gap energy decreased with increment of CeF3 content due to structural change with more population of NBO in the glass network. The Ce3+ excitation and emission peak positions shift towards longer wavelengths. The strong bands of emission centered between 325 – 347 nm, corresponding to Ce3+ 5d – 4f transition, were found in photoluminescence spectra. Those emission intensities under Ce3+ directly, 308 nm, excitation were higher than ones under Gd3+, 275 nm, excitation. The latter emission represents the high rate of energy transfer from Gd3+ to Ce3+. The optimum concentrations of CeF3 concentration in this glass is 2.00 mol% as it resulted the maximum emission intensity. The strongest emission band of x-ray induced optical luminescence is around 375 nm. The integrated scintillation efficiency of this emission for 2.0 mol% CeF3 doped glass was 9.6% compared with the 520 nm emission of BGO crystal. The most dominant decay times of Ce3+ in each glass was fast as between 17.3 - 29.4 ns that performs the rapid response with coming excitation energy. Preliminary studied showed the interesting potential of NaGdAlP-Ce glasses with strong and fast luminescence signal that can be applied as the scintillation material in a radiation detector. Acknowledgements This work was supported by Thailand Research Fund (TRF) through the Royal Golden Jubilee (RGJ) Ph.D. Program (Grant No. PHD/0100/2559) and Nakhon Pathom Rajabhat University. References [1] J. S. Neal, L. Boatner, D. J. Wisniewski, J. O. Ramey, New rare-earth-activated phosphate glass scintillators, P. Soc. Photo-Opt. Ins. 6706 (2007) 670618-1–670618-10. Nikl, J.A. Mares, E. Mihokova, K. Nitsch, N. Solovieva, V. Babin, A. Krasnikov, S. Zazubovich, M. Martini, A. Vedda, P. Fabenid, G.P. Pazzid, S. Baccaro, Radio- and thermoluminescence and energy transfer processes in Ce3+(Tb3+)-doped phosphate scintillating glasses, Radiat. Meas. 33 (2001) 593–596.

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