Photon Factory Activity Report 2018 #36 (2019)

Total luminescence yield of some scintillatorsin the photon energy region from 300 eV to 1.3 keV

BL-11D/2018G072

EJIMA, Takeo1,*, KUROSAWA, Shunsuke2,6, YAMAJI, Akihiro3, HATANO, Tadashi1, WAKAYAMA,
4
5
6
Toshitaka , HIGASHIGUCHI, Takeshi , KITAURA, Mamoru
1Institute of Multidisciplinary Research for Advanced Materials, Tohoku University,
2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan2
New Industry Creation Hatchery Center, Tohoku University,
6-6-10, Aramaki aza Aoba, Aoba-ku, Sendai, 980-8579, Japan
3
Institute for Materials Research, Tohoku University,
2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan
4
Faculty of Health and Medical Care, Saitama Medical University,
1397-1, Yamane, Hidaka, 350-1241, Japan
5
Faculty of Engineering, Utsunomiya University,
7-1-2, Yoto, Utsunomiya, 321-8585, Japan
6
Faculty of Science, Yamagata University,
1-4-12, Kojirakawa-machi, Yamagata, 990-8560, Japan

Total luminescence yield (TLY) spectra of scintillators were measured to identify which scintillator exhibited highluminosity in the SX region from 300 eV to 1.3 keV. The obtained TLY intensities were Tl:CsI, Eu:GGG, Ce:LYSO,Tb:LSO, Eu:YAP, and Ce:YAP in descending order of spectral intensity, which differs from the known intensities in thehard X-ray region.
1 Introduction
In recent years, some scintillators exhibited stimulatedemission suppression (STED) phenomenon, and theapplication of STED phenomenon to the 2D detector is
expected to further reduce pixel size in the detector plane[1]. A point for selecting luminescence materials on
applying the STED phenomenon is high intensity of theluminescence because detection efficiency will increase as
the increase of the luminescence intensity. In a photon
energy region from 300 eV to 1.3 keV, the component
atoms show many absorption edges in scintillators;
therefore, the luminosities of the scintillators in the SX
region differ from those in the HX region because of theabsorption of the scintillators. For example, the luminosityof Ce:LYSO, 33.8 photons/keV, is less than that of Tl:CsI,
61 photons/keV in the HX region [2], but the measuredluminosity of Ce:LYSO was comparable to that of Tl:CsI
in the extreme ultraviolet region [3]. In this study, the TLYsof scintillators were measured and compared in the SX
photon energy region.
2 Experimental
In the measurement, a small vacuum chamber wasplaced at around the focus point of SX beam from thebeamline, BL11D. A SX photodiode was installed in thevacuum chamber to measure the intensity of the incident
SX beam as shown in Fig. 1. The detector plane of the SX
photodiode was large enough to cover the beam size of theincident SX beam. A sample holder made from a Cu block
was placed at the focus point of the incident SX beam.

Samples were adhered on the sample holder using a black
carbon tape to reduce the stray light and a 3-mm diameterhole was made on the sample holder to prevent the lightreflection from the sample holder. The luminescence fromthe sample was emitted through an optical window (KovarGlass), and the extracted light was focused to a VI
photodiode for TLY measurements. Both the SX and theVI photodiode currents were measured with a picoammeter.
The wavelength resolutions at the measurement wereλ/δλ = 1000 and 500 in the SX and VI regions. The beam
size of the monochromatized SX beam can be changed
using the four-dimensional (4D) slit installed on thedownstream side of the exit slit of the monochromator. The
4D slit was adjusted so that a diameter of the focus point
was 1 mm or less. The measurements were made at bothroom temperature (RT) and the liquid nitrogen temperature(LNT) (< 85 K). For the TLY spectroscopic measurements,
the photon energy of the incident SX light was changedfrom 300 eV to 1.3 keV every 5 eV, and the exposure time
per step was 3 s. After the energy distribution curves ofTLY were normalized by both of that of the incident SX
intensity and exposure time, the TLY spectra of thescintillators were obtained.
3 Results & Discussion
The measurement results of the TLY spectra at the LNT
are shown in Fig. 2. In the figure, six spectral shapes wereselected and drawn from the measured scintillators because

Photon Factory Activity Report 2018 #36 (2019)

the TLY intensity of the other three scintillators (i.e.,
Ce:YAG, Ce:LuAG, and Eu:CaF2) were weak in thepresent energy region. The reflectance at the sample−8surface was calculated and the values were 1.0 × 10 orless in the measured SX region [4]; therefore, they are
negligibly small. The TLY spectra were also measured at
the downstream side of the sample through the hall back of
the sample using the SX photodiode because it showedsensitivity in the VI region. The results were consistentwith the results of Fig. 2, where the backside reflection
from the samples was considered to be small enough. Asfor the relative luminosities of the measured scintillators tothat of Ce:LYSO, Tl:CsI was about 200%, Eu:GGG wasabout 140%, Tb:LSO was about 75%, Eu:YAP was about50%, and Ce:YAP was about 35% in descending order ofstrength.
As can be seen in Fig. 2, the measured TLY intensities
increase as the excited photon energy increases. The
absorption coefficients of the base materials of the present
scintillators show that the values of absorption coefficientsdecrease as the incident photon energy increases; therefore,
the increase of the measured TLY intensities can beinterpreted as the increase of the product of an excitation
probability of excitons associated with both SX excitation
processes and the succeeding relaxation processes of theexcitation, and a luminescence probability associated withthe relaxation processes of the excitons.

[4] D. L. Windt, Comp. Phys. 12 (1998) pp. 360-370, doi:
10.1063/1.168689* takeo.ejima.e7@tohoku.ac.jp

Fig. 1：Layout of TLY measurements.

4 Summary
The luminosities of some scintillators were investigatedin a photon energy region from 300 eV to 1.3 keV. TLY
spectra of scintillators showing high luminosity in HX
region were measured and compared. The luminosities
obtained from the TLY intensities were different fromthose known in the HX region. The difference can be
explained by either or both the excitons excited by theincident X-rays and the accompanying the exciton
relaxations.
Acknowledgments
We are particularly grateful to Prof. K. Mase and Mr. T.
Kikuchi for their assistance in the measurements. This
work was supported by JSPS KAKENHI (grant numbers16H03902 and 17H190210).
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Douissard, T. Martin, Y. Zorenko, D. A. Vasil'ev, M.
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Fig. 2：TLY spectra of scintillators.