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Sensors and Materials, Vol. 36, No. 2 (2024) 573–578
MYU Tokyo
S & M 3546

Optical and Scintillation Properties ofCe-doped 20CsCl–20SrCl2–60ZnCl2 Glasses
Daisuke Nakauchi,1* Hiromi Kimura,2 Daiki Shiratori,3Takumi Kato,1 Noriaki Kawaguchi,1 and Takayuki Yanagida1
1Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
2National Institute of Advanced Industrial Science and Technology,

1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan

3Tokyo University of Science, 6-3-1 Niijuku, Katsushika, Tokyo 125-8585, Japan(Received October 30, 2023; accepted January 17, 2024)

Keywords: scintillator, phosphor, photoluminescence, radioluminescence, afterglow

Ce-doped 20CsCl–20SrCl 2 –60ZnCl 2 glasses were investigated for their optical andscintillation properties. Under X-ray irradiation, a broad emission peak at approximately 350 nmwith a shoulder peak at 375 nm was observed, and its origin was attributed to Ce3+. In the pulse
height spectrum under 241Am α-ray, the glass doped with 0.05% Ce exhibited the highest lightyield (LY) of 25 ph/MeV (138 ph/5.5MeV-α) among zinc-halide-based glasses. The afterglow
levels of the samples were superior to that of commercial CsI:Tl.

1.

Introduction

A scintillator is a type of phosphor with the function of converting absorbed radiation energy
to low-energy photons. The combination of a scintillator and a photodetector has been utilized asa scintillation detector in radiation detection, such as medicine,(1) security,(2) and resource
survey.(3) In general, a scintillator requires various properties, including high light yield (LY),short decay, suitable effective atomic number (Zeff ), and low afterglow.(4–6) Although single
crystal scintillators have been mainly studied for these applications,(7–13) glass forms havevarious industrial advantages such as low production cost, mechanical strength, and highmoldability in comparison with single crystal and ceramic forms.(13–16) However, only 6Li glass(GS20) has been practically used for measuring neutrons.(17–21) Efficient X-ray and γ-ray
measurements require glass scintillators to contain heavy elements.
To date, various glasses have been studied for scintillator applications: borate,(22) silicate,(23)phosphate,(24,25) tellurite,(26) and oxyfluoride glasses.(27) Among them, halide-based glasses havebeen studied for X-ray and γ-ray detection owing to their advantages such as low phonon energy.
Zinc halides are able to form a glass matrix by themselves, and the phonon energy is lower thanthose of oxide- or fluoride-based glasses. Thus far, rare-earth-doped ZnCl2-based glasses haveattracted attention for phosphor uses.(28–35) In our previous works, we studied 20CsCl-20BaCl2*Corresponding author: e-mail: nakauchi@ms.naist.jp

https://doi.org/10.18494/SAM4750

ISSN 0914-4935 © MYU K.K.
https://myukk.org/

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60ZnCl2(36,37) and 20CsBr–20BaBr2–60ZnBr2(38,39) glasses for radiation measurements owing
to their Zeff (42–43) being larger than that of GS20 (Zeff~25.5), and the Ce-doped ones enabledenergy distribution measurements using a radioisotope. To confirm the change trend ofscintillation properties depending on alkaline earth cations, Ce-doped 20CsCl–20SrCl2–60ZnCl2 (CSZ) glasses (Zeff~38.3) were investigated for optical and scintillation measurements.

2.

Data, Materials, and Methods

20CsCl–20SrCl2–60ZnCl2 glasses doped with 0.05, 0.1, 0.5, 1.0, and 3.0% Ce were preparedby the melt quenching method. CsCl (4N), SrCl2 (4N), ZnCl2 (4N), and CeCl3·6H2O (4N) wereused as raw powders. They were dried in vacuum at 200 ℃ for 1 h in a quartz tube and thenenclosed using a gas burner.(40) After the powders were heated for 1 h at 700 ℃ using an electric
furnace, the sealed ampule was dropped into water at room temperature to rapidly cool. To
confirm an amorphous phase, powder X-ray diffraction (XRD) analysis was performed using
MiniFlex-600, Rigaku. To measure the photoluminescence (PL) spectra and QY, QuantaurusQY C11347 (Hamamatsu Photonics) was used. X-ray-induced radioluminescence (XRL) spectra,
kinetic decay, afterglow, and pulse height were evaluated using our laboratory-made setup.(41,42)

3.

Results and Discussion

The prepared samples after polishing are shown in Fig. 1, and no significant differences inappearance are observed for all the samples. The samples have a cloudy and colorlessappearance, which is due to the rapid deliquescence of their surface. To confirm that the samples
are amorphous, the XRD patterns were evaluated as shown in Fig. 1. In all the samples, broad
signals peaking at 12 and 20 degrees are observed. This halo peak suggests the formation of aglass matrix. In addition, no crystalline phase is observed at the detection limit in the XRD

Fig. 1.

(Color online) XRD patterns of CSZ glasses.

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measurements. PL spectra are measured to reveal general phosphor properties. All the samples
show similar spectral features, and Fig. 2 shows the spectrum of the 0.05% Ce-doped sample asa representative spectrum. The sample shows a broad emission band peaking at 370 nm, which isalmost the same emission wavelength as those of past zinc-halide-based glasses.(37,38) The QY
values under excitation at 320 nm are 88.1% for the 0.05% Ce-doped sample, 89.4% for the 0.1%
Ce-doped sample, 85.2% for the 0.3% Ce-doped sample, and 81.9% for the 0.5% Ce-dopedsample, and QY increases up to the optimal concentration (0.05%) and decreases at higher
concentrations.
Figure 3 shows the XRL spectra of the samples. Similar to PL, all the samples show a broademission peak peaking at ~370 nm. As the Ce concentration increases, the absorption near 350
nm increases, and the spectral features indicate a peak shift; the results are consistent with thePL spectra. To confirm the response speed as a scintillator, XRL decay curves were evaluated asshown in Fig. 4. The least squares approximation shows that the decay curves have twocomponents. The obtained decay values are close to those of zinc-halide-based glasses reported
in previous studies, and this result is attributed to the 5d–4f transitions of Ce. The decay timetends to increase with the Ce concentration, and this tendency is also the same as those of otherzinc-halide-based glasses.
The pulse height spectra under 241Am α-ray irradiation measured using the prepared samples
and reference GS20 (1255 ph/MeV under α-ray(24)) are shown in Fig. 5. In all the samples, a clear
full energy peak of α-rays (5.5 MeV) is observed, and the calculated LYs are approximately 22
ph/MeV for 0.05%, 21 ph/MeV for 0.1%, 25 ph/MeV for 0.3%, and 24 ph/MeV for 0.5% dopedsamples. These LYs are slightly higher than those of the other zinc-halide-based glasses (~23 ph/
MeV in Ce-doped CsCl–BaCl2–ZnCl2(37) and ~7 ph/MeV in Ce-doped CsBr–SrBr2–ZnBr2(38)).
Figure 6 shows the afterglow profiles observed after 2 ms X-ray irradiation. To compare

Fig. 2.

(Color online) PL contour maps of CSZ glasses.

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Fig. 3.

(Color online) XRL spectra of CSZ glasses.

Fig. 4. (Color online) XRL decay curves of CSZ
glasses.

Fig. 5. (Color online) Pulse height spectra of 241Am
α-rays measured using CSZ glasses.

Fig. 6. (Color online) X-ray-induced afterglow
curves of CSZ glasses.

afterglow levels, the afterglow level at 20 ms after X-ray irradiation was stopped (AG20ms) wasdefined in the same manner as in the previous papers.(43,44) The afterglow levels of the 0.05, 0.1,0.3, and 0.5% Ce-doped glasses are respectively 245, 230, 138, and 233 ppm, which are slightly
superior to that of commercial CsI:Tl (~300 ppm(44)) and higher than that of Ce-doped CsClBaCl2-ZnCl2 glasses (~60 ppm).(37)4.

Conclusions

Ce-doped 20CsCl–20SrCl2–60ZnCl2 glasses were synthesized to evaluate their scintillation
properties. Under UV light or X-ray irradiation, the prepared glasses showed a broad emission
band peaking at 370 nm, and peak positions slightly redshifted with increasing Ce concentration.
XRL decay curves showed that decay time constants are approximately 20–30 ns, which areSensors and Materials, Vol. 36, No. 2 (2024)

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reasonable for the 5d–4f emission of Ce. In the pulse height spectra under 241Am α-ray
irradiation, a full energy peak was observed in all the samples, and the 0.3% doped sample
showed the highest LY of 25 ph/MeV (138 ph/5.5MeV-α) under α-rays among the samples. TheAG20ms values of the samples were approximately 100–300 ppm, which were superior to those ofcommercial CsI:Tl scintillators. Considered comprehensively from LY and AG20ms, the 0.3% Cedoped glass is the most suitable for scintillator uses among the present glasses. The obtainedsamples were superior to all reported zinc-halide-based glasses, but were inferior to practical
GS20 except for Zeff and QY. Some zinc-halide-based glasses exhibit higher QYs than GS20 butlower LYs than GS20. The cause is considered to be the low energy transport efficiency despite
the low phonon energy, but the actual cause is unclear at present. The development of halide
glasses to overcome this problem is expected.

Acknowledgments
This work was supported by Grants-in-Aid for Scientific Research A (22H00309), Scientific
Research B (22H03872, 22H02939, 21H03733, and 21H03736), Early-Career Scientists(23K13689), and Challenging Exploratory Research (22K18997) from JSPS. The Cooperative
Research Project of the Research Center for Biomedical Engineering, A-STEP from JST,Kazuchika Okura Memorial Foundation, Asahi Glass Foundation, Nakatani Foundation, andKonica Minolta Science and Technology Foundation are also acknowledged.

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