Flexible composite scintillators based on ZnWO₄ micro- and nanopowders
Nano-sized and micro-sized ZnWO₄ powders were obtained by different methods: hydrothermal synthesis with microwave heating, molten salt method, solid-state synthesis and сrushing of bulk crystals. Their morphological features were studied using transmission electron microscope and scanning electron...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
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nasplib_isofts_kiev_ua-123456789-1678672025-02-09T15:32:19Z Flexible composite scintillators based on ZnWO₄ micro- and nanopowders Гибкие композиционные сцинтилляторы на основе микро- и нанопорошков ZnWO₄ Гнучкі та композиційні сцинтилятори на основі мікро- та нанопорошків ZnWO₄ Tinkova, V.S. Yakubovskaya, A.G. Tupitsyna, I.A. Abashin, S.L. Abashin, S.L. Tretyak, S.O. Материалы электроники Nano-sized and micro-sized ZnWO₄ powders were obtained by different methods: hydrothermal synthesis with microwave heating, molten salt method, solid-state synthesis and сrushing of bulk crystals. Their morphological features were studied using transmission electron microscope and scanning electron microscope. The obtained nano- and micro-sized powders were used as fillers for flexible composite scintillators. The silicon rubber was used as a binder. The luminescent characteristics and scintillation performance of composite scintillators were measured. The dependence of scintillation performance of flexible scintillators on the morphological features of ZnWO₄ nanocrystallites was demonstrated. The flexible composite scintillator based on zinc tungstate obtained by solid-state synthesis with lithium nitrate addition was obtained and investigated. Its scintillation performance was close to that of a ZnWO₄ single crystal. В настоящей работе проведены исследования, направленные на поиск эффективного способа получения порошка ZnWO₄ для разработки гибких композиционных сцинтилляторов с высокими функциональными характеристиками, такими как световой выход и уровень послесвечения. У даній роботі проведені дослідження, спрямовані на пошук ефективного способу отримання порошку ZnWO₄ для розробки гнучких композиційних сцинтиляторів з високими функціональними характеристиками, такими як світловий вихід і рівень післясвітіння. 2019 Article Flexible composite scintillators based on ZnWO₄ micro- and nanopowders / V.S. Tinkova, A.G. Yakubovskaya, I.A. Tupitsyna, S.L. Abashin, A.N. Puzan, S.O. Tretyak // Технология и конструирование в электронной аппаратуре. — 2019. — № 1-2. — С. 40-49. — Бібліогр.: 26 назв. — англ. 2225-5818 DOI: 10.15222/TKEA2019.1-2.40This https://nasplib.isofts.kiev.ua/handle/123456789/167867 539.1.074.3 : 62-492.2 : 546.47'78'21 en Технология и конструирование в электронной аппаратуре application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Материалы электроники Материалы электроники |
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Материалы электроники Материалы электроники Tinkova, V.S. Yakubovskaya, A.G. Tupitsyna, I.A. Abashin, S.L. Abashin, S.L. Tretyak, S.O. Flexible composite scintillators based on ZnWO₄ micro- and nanopowders Технология и конструирование в электронной аппаратуре |
| description |
Nano-sized and micro-sized ZnWO₄ powders were obtained by different methods: hydrothermal synthesis with microwave heating, molten salt method, solid-state synthesis and сrushing of bulk crystals. Their morphological features were studied using transmission electron microscope and scanning electron microscope. The obtained nano- and micro-sized powders were used as fillers for flexible composite scintillators. The silicon rubber was used as a binder. The luminescent characteristics and scintillation performance of composite scintillators were measured. The dependence of scintillation performance of flexible scintillators on the morphological features of ZnWO₄ nanocrystallites was demonstrated. The flexible composite scintillator based on zinc tungstate obtained by solid-state synthesis with lithium nitrate addition was obtained and investigated. Its scintillation performance was close to that of a ZnWO₄ single crystal. |
| format |
Article |
| author |
Tinkova, V.S. Yakubovskaya, A.G. Tupitsyna, I.A. Abashin, S.L. Abashin, S.L. Tretyak, S.O. |
| author_facet |
Tinkova, V.S. Yakubovskaya, A.G. Tupitsyna, I.A. Abashin, S.L. Abashin, S.L. Tretyak, S.O. |
| author_sort |
Tinkova, V.S. |
| title |
Flexible composite scintillators based on ZnWO₄ micro- and nanopowders |
| title_short |
Flexible composite scintillators based on ZnWO₄ micro- and nanopowders |
| title_full |
Flexible composite scintillators based on ZnWO₄ micro- and nanopowders |
| title_fullStr |
Flexible composite scintillators based on ZnWO₄ micro- and nanopowders |
| title_full_unstemmed |
Flexible composite scintillators based on ZnWO₄ micro- and nanopowders |
| title_sort |
flexible composite scintillators based on znwo₄ micro- and nanopowders |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2019 |
| topic_facet |
Материалы электроники |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/167867 |
| citation_txt |
Flexible composite scintillators based on ZnWO₄ micro- and nanopowders / V.S. Tinkova, A.G. Yakubovskaya, I.A. Tupitsyna, S.L. Abashin, A.N. Puzan, S.O. Tretyak // Технология и конструирование в электронной аппаратуре. — 2019. — № 1-2. — С. 40-49. — Бібліогр.: 26 назв. — англ. |
| series |
Технология и конструирование в электронной аппаратуре |
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| fulltext |
Tekhnologiya i Konstruirovanie v Elektronnoi Apparature, 2019, No 1–2
40 ISSN 2225-5818
MATERIALS OF ELECTRONICS
1
UDC 539.1.074.3 : 62-492.2 : 546.47'78'21
V. S. TINKOVA1, A. G. YAKUBOVSKAYA1, I. A. TUPITSYNA1, S. L. ABASHIN2,
A. N. PUZAN3, S. O. TRETYAK1
Ukraine, Kharkov, 1Institute for Scintillation Materials NAS of Ukraine;
2National Aerospace University “Kharkiv Aviation Institute”;
3SSI “Institute for Single Crystals” NAS of Ukraine
E-mail: zvereva@isma.kharkov.ua
FLEXIBLE COMPOSITE SCINTILLATORS BASED
ON ZnWO4 MICRO- AND NANOPOWDERS
There is now an ongoing research of effective
technological methods for obtaining materials
suitable for use in modern scintillation detectors
(for nondestructive testing, digital radiography
and X-ray, a, b, g and neutron registration). The
creation of composite scintillators based on mi-
cro- and nanoscale crystal powders [1] obtained
by various methods [2—4] is a promising research
direction in this field.
It was expected that using nano-sized materi-
als would allow developing qualitatively new
scintillators with functional characteristics that
would satisfy the modern requirements (spatial,
spectrometric and temporal resolution, sensitiv-
ity, radiation hardness, low afterglow) [5, 6].
The properties of nano-sized scintillation powders
significantly depend on their size and morphology,
and controlling this parameters allows producing
scintillation detectors with high performance [7].
Zinc tungstate (ZnWO4) is a promising mate-
rial that could be a successful replacement for
cadmium tungstate which contains toxic cadmium.
It is possible because ZnWO4 has the unique
combination of properties (high density, high
effective atomic number, small radiation length
and scintillation performance) similar to those
of cadmium tungstate. Therefore, ZnWO4 can
be used in X-ray, gamma and neutron radiation
Nano-sized and micro-sized ZnWO4 powders were obtained by different methods: hydrothermal synthesis
with microwave heating, molten salt method, solid-state synthesis and сrushing of bulk crystals. Their
morphological features were studied using transmission electron microscope and scanning electron
microscope. The obtained nano- and micro-sized powders were used as fillers for flexible composite
scintillators. The silicon rubber was used as a binder. The luminescent characteristics and scintillation
performance of composite scintillators were measured. The dependence of scintillation performance of
flexible scintillators on the morphological features of ZnWO4 nanocrystallites was demonstrated. The
flexible composite scintillator based on zinc tungstate obtained by solid-state synthesis with lithium
nitrate addition was obtained and investigated. Its scintillation performance was close to that of
a ZnWO4 single crystal.
Keywords: zinc tungstate, nano-sized crystals, micro-sized powders, composite scintillators, light output,
afterglow.
detectors in homeland security systems and for
non-destructive testing.
Thus, the primary task of the work was to
choose the best method to produce ZnWO4 pow-
der for development of high performance flexible
composite scintillators.
Research methodology
ZnWO4 single crystals grown by Czochralski
method [8] were used to obtain powders with
different grains sizes. The crushing of ZnWO4
single crystals was carried out with laboratory
mechanical mortar Retch RM 200. The following
fractionation was carried out with vibratory sieve
shaker Retch AS 200 using sieves No 0080, 0100,
0140, 0200, 0250.
For the preparation of 0.1 M aqueous solu-
tions Zn(NO3)2⋅6H2O (99.9%) and Na2WO4⋅2H2O
(>99.9%) were used. Before the synthesis the
solutions were mixed with a ratio of 1:1. The
pH of the mixture was changed by addition of
30% NH3⋅H2O solution (99%). ZnWO4 powder
was synthesized from the obtained mixture by
microwave-hydrothermal method.
ZnO (99.995%) and WO3 (99.995%) were used
as starting materials for the synthesis of ZnWO4
scintillation powder by molten salt and solid-state
methods. LiNO3⋅6H2O (99.9%) was used as a low-
temperature solvent and as a mineralizer in molten
salt and solid-state methods, respectively.
Morphology of the nano-sized crystals was de-
termined using transmission electron microscope
DOI: 10.15222/TKEA2019.1-2.40
This work was supported by National Academy of Science
of Ukraine through grant of young scientists’ project of
NAS of Ukraine in 2017, contract No. 51-2017.
Tekhnologiya i Konstruirovanie v Elektronnoi Apparature, 2019, No 1–2
41ISSN 2225-5818
MATERIALS OF ELECTRONICS
2
(TEM) EM-125 (SELMA, Ukraine). Electron
accelerating voltage was 125 keV, the survey was
carried out in the bright field mode, and the image
was recorded by CCD matrix. The carbon films
coated with water suspension of the investigated
powders were used for electron microscopy.
Morphology of the micro-sized crystals was
determined using scanning electron microscope
(SEM) REM-100U with energy dispersive attach-
ment EDAR.
X-ray diffraction study (XRD) was carried out
using Siemens D500 automated powder diffrac-
tometer (CuKaαradiation, Ni filter, 5° ≤ 2q ≤ 110°,
D2q = 0.02°, delay time of 24 s per point). Rietveld
refinement of obtained pattern was carried out
with FullProf and WinPLOTR software packages
[9]. Cell dimensions, anisotropic profile function,
background function and systematic instrumental
errors were taken into account.
Flexible scintillation composite samples
(∅30×2 mm) based on ZnWO4 powders obtained
by different methods were prepared. The heat-
resistant low molecular silicone rubber was used as
a binder. The luminescent and scintillation char-
acteristics of the composite samples were investi-
gated. ZnWO4 and CdWO4 polished plates with
size of 10×10×2 mm were used as references during
the measurements of scintillation performances.
Both reference plates were cut from crystals grown
by Czochralski method. The light yield of CdWO4
was measured in [10] as 19500 ph/MeV.
X-ray luminescence spectra were measured by
spectrometric complex KSVU-23. REIS (Ua ≤ 40 keV,
Ia ≤ 50 μA) X-ray source was used for excitation.
Light output of the investigated composite
samples was measured in scanning mode with
respect to ZnWO4 and CdWO4 single crystals
by the scheme which is presented in Fig. 1. The
objective table 3 with investigated samples moves
between the photodetector 5 and X-ray tube (fo-
cal spot 0.8 mm) in a plane XY with a step of
3 mm, which can be changed in manual mode. X-ray
transmission optical scheme was used during measure-
ments. The different light collection conditions were
considered. X-ray source (Ua = 100 keV, Ia = 1 mА)
was used for excitation. The measurement error of
the light output was 12%.
The afterglow level was determined by means of
a measuring set up which included a pulsed X-ray
source RAPAN 200/100 (Ua =130—180 kV, irra-
diation time 2 s), a control unit, a Si-photodiode
S8594, a current-to-voltage converter, a multiplex-
er, an analog-to-digital converter, and a computer
with an appropriate software. The measurement
error of the afterglow level was 10%.
Experimental results and discussion
Flexible composite scintillators based on ZnWO4
obtained by crushing of bulk crystals
Micro- and nanocrystallites ZnWO4 used as
fillers for composite scintillators were obtained by
crushing of bulk crystals [11]. The advantages of
the method are the high speed of the process and
the simplicity of the milling hardware. The feature
of the method is wide particles size distribution
of resulting crystallites (from several nanometers
to hundreds of micrometers).
As a result of ZnWO4 single crystal crushing we
obtained the following ratio of the particle size frac-
tions: more than 280 μm was 4.5%; 140—280 μm
was 33.5%; 80—140 μm was 26%, less than 80 μm
was 36% [12]. The composite sample (further
denoted as ZWO-30) based on as-crushed crystal
was prepared. During the polymerization of the
binder the sedimentation of ZnWO4 particles
takes place. Large particles settle on the bottom
of the mold for casting, while particles of several
tens of nanometers remain in suspension forming
a dense composite surface. SEM-evaluation of the
composite scintillator surfaces has shown that
ZnWO4 particles about 250 nm in size were located
on the top side and particles with average size of
250 μm were on the bottom side of the composite
sample. (Further these surfaces will be denoted as
ZWO-30-250nm and ZWO-30-250μm, respectively.)
The light output of the obtained samples was
determined by two methods, i. e. the light output
Fig. 1. Scheme of light output measurements:
1 — X-ray source; 2 —collimator; 3 —objective table;
4 —protective filter; 5 —photodetector; 6 —amplifier
6
5
4
3
2
1
X
Y
Y
X
Tekhnologiya i Konstruirovanie v Elektronnoi Apparature, 2019, No 1–2
42 ISSN 2225-5818
MATERIALS OF ELECTRONICS
3
was estimated by cathodoluminescence technique
and measured under X-ray excitation.
The technique for measuring light output under
cathode excitation is described in [11]. It should
be noted that the experimental conditions of light
output estimation used in [11] have minimized the
influence of light collection due to reflection-type
optical scheme in the measurements of catodolu-
minescence intensity.
The light output was determined for the
both sides of the sample (ZWO-30-250nm and
ZWO-30-250μm) based on the cathodolumines-
cence results. The penetration depth of the high-
energy electron beam into the surface was very
small and only luminescence of the surface layers
was observed under irradiation. The light output
of the ZWO-30-250nm (97 a. u.) was almost twice
higher than that of the ZWO-30-250μm (45 a. u.)
and the ZnWO4 single crystal (46 a. u.) [11].
The light output of the ZWO-30 under X-ray
excitation was determined using the optical trans-
mission scheme shown in Fig. 1. The light output
of the ZWO-30 under X-ray excitation was mea-
sured from both top and bottom sides (Table 1).
The ZWO-30 sample and ZnWO4 single crystal
reference were placed on a white diffuse reflector.
The relative light outputs of ZWO-30-250μm and
ZWO-30-250nm were 280% and 227% of ZnWO4
single crystal, respectively. It could be due to
size gradient distribution of particles through the
thickness of the composite samples (as a conse-
quence of the sedimentation described above) [12].
As a result, the best light collection conditions
for this measurement method were achieved on
ZWO-30-250μm. Further in the article it will be
shown that the change of light collection condi-
tions shows significant effect on the light output
of composite scintillators.
The measurement results demonstrate that the
described preparation method of scintillation pow-
der allows obtaining composite scintillators based
on ZnWO4 with high scintillation performance.
However, mass production of such composite scin-
tillators is expensive. Therefore, it is desirable to
find ways of preparing ZnWO4 powder with good
scintillation characteristics by passing the growth
stage and the following crushing of a single crystal.
Flexible composite scintillators based on ZnWO4
obtained by hydrothermal synthesis with micro-
wave heating
Hydrothermal synthesis with microwave heat-
ing allows controlling all parameters of the reac-
tion (time, temperature, pressure), which ensures
homogeneous nucleation process under homoge-
neous heating of the reaction mixture and yields in
dispersion of high purity with a specified narrow
particle size distribution [13]. The method also
allows obtaining specified morphology of nano-
crystals, which directly relates to the electronic
structure, binding energy and surface energy [14].
The hydrothermal synthesis of zinc tungstate
nanocrystals was carried out using microwave heat-
ing of aqueous solutions of Zn(NO3)2⋅6H2O and
Na2WO4⋅2H2O (pH = 6.5—9.5) at temperatures of
120—200°C for 30 min [14]. The results of XRD
(Fig. 2) showed that the nucleation of ZnWO4
nanocrystals with a monoclinic wolframite struc-
ture (JCDPS No 15-0774 [15]) begins at 120°C.
The increase in temperature and pH accelerates
the growth of the crystallites.
The investigation of ZnWO4 nanopowders
morphology using TEM showed that samples syn-
thesized at pH = 9.5 and temperature of 120°C,
consisted of “grain” nanoparticles with a size
of 25—50 nm, while those synthesized at 200°C
Fig. 2. X-ray diffraction patterns of ZnWO4 nanocrystals
obtained by hydrothermal synthesis with microwave
heating at pH = 9.5 and different temperature values
3
2
1
0
10 20 30 40 50 60 2q, °
In
te
ns
it
y,
a.
u
.
(0
10
)
(1
00
)
(0
11
)
(1
10
) (1
11
)
(0
21
)
(2
00
)
(1
21
)
(0
22
)
(2
20
)
(1
12
)
(2
11
)
(1
30
)
(1
13
)
(3
11
)
(0
41
)
Table 1
The light output under X-ray excitation of composite
scintillators based on ZnWO4 obtained by different
methods
Method Sample Light
output, %
Czochralski
Polished ZnWO4
single crystal 100
Crushed crystal
ZWO-30-250µm 280
ZWO-30-250nm 227
Hydrothermal
synthesis with
microwave
heating
ZWO-25g 16
ZWO-100r 23
ZWO-200r 30
Molten salt
synthesis ZWO-MSМ 67
Solid-state
synthesis
ZWO-SSS 155
ZWO-SSS-LiNO3 272
Tekhnologiya i Konstruirovanie v Elektronnoi Apparature, 2019, No 1–2
43ISSN 2225-5818
MATERIALS OF ELECTRONICS
4
consisted of “rod” nanoparticles of 250—300 nm
in length and 30 nm in diameter (Fig. 3). Such
a preferential growth along one of the crystallo-
graphic directions is explained by the anisotropic
structure of ZnWO4.
X-ray luminescence spectra investigation of the
obtained powders showed the presence of a band
with lmax ≈ 500 nm. This band is typical for ZnWO4
single crystals and is caused by the emission of self-
trapped excitons in the WO6
6 - oxyanion complex
[16]. Fig. 3 illustrates the dependence of X-ray
luminescence intensity on the morphology (sizes)
of nanopowders synthesized at different conditions.
Emission intensity of the “grains” is nearly zero
(curve 1), while for “rods” the luminescence inten-
sity (curve 3) is typically high for ZnWO4. Similar
dependences were observed in nanocrystals of dif-
ferent oxygen-containing compounds [17—19].
Such a big difference between curve 1 and curve 3
could be explained by the fact that the decreasing
of nanocrystal sizes leads to an increase in oxygen
vacancies, which in turn causes the formation of
WO6 octahedra with distorted structure (lumi-
nescence centers with low probability of photon
emission) [20]. It was shown that red luminescence
is associated with the distorted complexes. The
photoluminescence spectra of nano-sized ZnWO4
samples excited by irradiation with a wavelength
of lex= 355 nm contain a red emission band at
700 nm (Fig. 4). The intensity of the red band
increases with the decrease of the ZnWO4 nano-
crystals size. At the same time the intensity of the
red band for the samples annealed in air decreases,
which indicates the healing of oxygen vacancies
and decrease in concentration of distorted WO6
octahedra.
As it was shown in [20], that annealing of
ZnWO4 nanopowders in air leads to a significant
increase in X-ray luminescence intensity of the
“grains” and has virtually no effect on intensity
of the “rods” (Fig. 5).
1
2
400 500 600 700
Wavelenght l, nm
Fig. 4. Photoluminescence spectra of ZnWO4 “grains”
before (1) and after annealing in air (2)
In
te
ns
it
y,
a
.
u.
lex= 355 nm
8
6
4
2
0
3
2
1
400 450 500 550 600 650
Wavelenght l, nm
In
te
ns
it
y,
a
.
u.
Fig. 3. X-ray luminescence spectra of ZnWO4
nanopowders obtained by hydrothermal synthesis
with microwave heating at pH = 9.5 and different
temperature values:
1 — 120°С; 2 — 160°С; 3 — 200°С
5
4
3
2
1
0
4
3
2
1
400 450 500 550 600 650
Wavelenght l, nm
Fig. 5. X-ray luminescence spectra of ZnWO4
nanopowders:
1 —“grains”; 2 —“grains” after annealing; 3 —“rods”;
4 —“rods” after annealing
In
te
ns
it
y,
a
.
u.
4
3
2
1
0
Tekhnologiya i Konstruirovanie v Elektronnoi Apparature, 2019, No 1–2
44 ISSN 2225-5818
MATERIALS OF ELECTRONICS
5
Under X-ray excitation, the red luminescence
is absent even in the samples with high oxygen
vacancy concentration. A competing nonradiative
relaxation channel is formed in WO6 octahedra
before air annealing, which causes a decrease in
the luminescence intensity of the main emission
band. After air annealing, the concentration of the
distorted WO6 octahedra decreases, simultaneously
increasing the main band intensity. This could pos-
sibly explain the increase in the intensity of the
main band in X-ray luminescence spectrum after
annealing the samples in air.
Composite samples with sizes of 10×10×2 mm
were based on the obtained ZnWO4 nanopowders.
The light outputs of the composite samples were
measured with reference to the ZnWO4 single
crystal (10×10×2 mm). The results of the measure-
ments are shown in Table 1 (ZWO-25g contained
“grains” of 25 nm, ZWO-100r — “rods” of 100 nm in
length, ZWO-200r — “rods” of 200 nm in length).
The data in Table 1 show an increase of light
output with the increase in nanoparticles size.
However, the light output of the nanodispersed
samples does not exceed 30% of that of the single
crystal sample. Thus, this method does not ensure
obtaining a scintillation material of the required
quality.
Flexible composite scintillators based on ZnWO4
obtained by molten salt synthesis
Synthesizing nanomaterials using a low-temper-
ature solvent offers the following advantages: the
simplicity of the required equipment and a high
efficiency of the particles obtained at tempera-
tures below the melting point of the synthesized
substance [21].
Single-phase nanocrystalline samples of the
ZnWO4 scintillator were obtained by molten salt
method (MSM) using a low-temperature LiNO3
solvent at 270°C for 6 and 16 hours [22]. The
original sample was amorphous ZnWO4 obtained
by co-precipitation method. Then, the precipitate
was mixed with lithium nitrate in a ratio of 1:6
and 1:10.
The investigation of powder morphology using
TEM showed that the largest granules (100 nm)
were synthesized at ZnWO4/LiNO3 ratio of 1:10
after synthesizing (annealing) for 16 hours (Fig. 6).
The size of nanocrystals obtained at other synthesis
conditions was less than 100 nm.
Table 2 shows the XRD data and calculated
on their basis unit cell parameters of ZnWO4
nanocrystals obtained under different synthesis
conditions (different ZnWO4/LiNO3 ratios and
different synthesis time periods). The crystal
lattice of nanocrystals is markedly distorted in
comparison with the ICDD database data for zinc
tungstate ZnWO4 (JCDPS No 15-0774 [15]). This
is particularly noticeable in the changing of the
unit cell volume. There is a tendency for crystal
lattice distortion to reduce (in particular, the
lattice volume parameter V) with the increase
of the synthesis time at the same lithium nitrate
concentration. The similar influence of synthesis
conditions on the crystal lattice parameters was
reported in [23].
Table 2
Unit cell parameters of ZnWO4 nanocrystals obtained under different synthesis conditions, compared
to the data for zinc tungstate presented in [15]
Ratio
ZnWO4:LiNO3/
time
a, Å b, Å c, Å β,° V, Å3
1:6 / 6 h 4.68266(9) 5.75328(12) 4.94864(8) 90.6305(11) 133.311(4)
1:10 / 6 h 4.68258(9) 5.75424(12) 4.94881(8) 90.6352(12) 133.336(4)
1:6 / 16 h 4.68341(8) 5.74941(11) 4.94598(88) 90.6362(10) 133.171(4)
1:10 / 16 h 4.68340(9) 5.74908(11) 4.94544(8) 90.6386(10) 133.149(4)
ZnWO4 [15] 4.69264 5.71546 4.92691 90.627 132.135
Fig. 6. TEM image of the nanopowder obtained by
molten salt synthesis at the following conditions:
ZnWO4/LiNO3 ratio of 1:10 after annealing for
16 hours
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The X-ray luminescence spectra of the obtained
powders show that nanosized crystal samples with
less distorted crystal lattices demonstrate better
scintillation performance. The highest lumines-
cence intensity was demonstrated by the sample
synthesized at the following conditions: ZnWO4/
LiNO3 ratio of 1:10 after annealing for 16 hours
(Fig. 7). X-ray luminescence intensity of the
obtained powders decreases with reduction in an-
nealing time and concentration of low-temperature
solvent.
The light output under X-ray excitation and
the afterglow level of composite scintillator based
on the ZnWO4 powder obtained by the molten
salt method (ZnWO4/LiNO3 = 1:10, 16 h) are
shown in Table 1 (ZWO-MSM) and Table 3,
respectively.
The light output of the ZWO-MSМ sample
was 67% of that of the ZnWO4 single crystal (see
Table 1). However, the afterglow level of ZWO-
MSМ is almost 2 times lower in the time range of
3—5 ms than that of the ZWO-30-250mm, which
is very important for using these scintillators in
computer tomography.
The improvement of the afterglow level of
the scintillators can be explained by the entry of
lithium ions from the solvent into the ZnWO4
crystal lattice, thus compensating the uncontrolled
impurities charge (in particular, trivalent metal
ions). This leads to changes in the defect structure
and, as a result, to disappearing of deep charge
traps. A similar effect of the lithium impurities on
the afterglow was observed for cadmium tungstate
crystals [24].
Flexible composite scintillators based on ZnWO4
obtained by solid-state synthesis
The most commonly used method for prepar-
ing of micro-sized oxide powders is solid-state
synthesis (SSS), which is quite simple
in technical realization. The use of a
low-melting salt as a mineralizer (up
to 10 wt. %) is one of the ways to ac-
celerate solid-state reactions. The min-
eralizer reduces synthesis temperature,
forms a melt, improves the diffusion of
reagents and accelerates the growth of
grains [25, 26].
As can be seen in the SEM images in
Fig. 8, after 50 h long synthesis without
1
2
3
4
400 450 500 550 600 650
Wavelenght l, nm
Fig. 7. The X-ray luminescence spectra of nanopowders
obtained by molten salt synthesis under difference
conditions (ratio ZnWO4:LiNO3, synthesis time):
1 — 1:10,16 h; 2 — 1:6,16 h; 3 —1:6, 6 h; 4 — 1:10, 6 h
In
te
ns
it
y,
a
.
u.
6000
4000
2000
0
Fig. 8. SEM images of ZnWO4 crystallites synthesized
at 950°С for 50 hours without a mineralizer (a) and
with LiNO3 (b)
a)
b)
Table 3
The afterglow level of ZnWO4 composite scintillators under
X-ray excitation
Sample Granule
sizes
Afterglow level, %, after different
periods of time
3 ms 5 ms 10 ms 20 ms
Polished ZnWO4
single crystal — 0.19 0.11 0.13 0.07
ZWO-30-250µm 250 μm 0.14 0.103 0.068 0.045
ZWO-MSМ 100 nm 0.072 0.064 0.055 0.047
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the mineralizer, the sizes of the obtained ZnWO4
grains were 0.5—2 μm, while after the synthesis
under the same conditions but with the addition
of lithium nitrate the sizes were 20—30 μm.
Fig. 9 shows the samples location on the objec-
tive table when measuring the light output under
X-ray excitation. For clarity, the white diffuse
reflector is shown in dark gray. The light output of
the composite samples (estimated under X-ray exci-
tation using the optical transmission scheme shown
in Fig. 1) is presented in Fig. 10 and Table 4.
The samples were placed on the objective table
and the light output throughout the scintillation
sample was measured at 3 mm step. The light out-
put of the sample was determined as the average
value over the entire area.
Fig. 9. The location scheme of samples on an objective table when measuring light output under X-ray excitation:
a — all samples are placed on a white diffusion reflector; b — all sides of the samples, except the top, are covered
with a white diffusion reflector; c — only the crystals are covered with a white diffusion reflector (all sides except
the top); d — only the crystals are covered with a white diffusion reflector (bottom side only)
1 — ZnWO4 single crystal (10×10×2 mm); 2 —CdWO4 single crystal (10×10×2 mm); 3— ZWO-30-250μm;
4—ZWO-SSS; 5 —ZWO-SSS-LiNO3
a)
1 3 4 5
2
1 3 4 5
2
b)
1 3 4 5
2
c)
1 3 4 5
2
d)
Fig. 10. Light output area distribution of different
samples:
1— single crystal ZnWO4; 2 — single crystal CdWO4;
3 — ZWO-30-250μm; 4 —ZWO-SSS; 5 —ZWO-SSS-LiNO3
L
ig
ht
o
ut
pu
t,
a
.
u.
Lenght
W
id
th
1
2
3
4
5
600
400
200
0
0—100; 100—200; 200—300; 300—400;
400—500; 500—600; 600—700
Table 4
The light output under X-ray excitation of scintillation samples under different light collection conditions
Light output collection
conditions
Light output, %
CdWO4
single
crystal
ZnWO4
single
crystal
ZWO-
30-250
µm
ZWO-
SSS
ZWO-
SSS-
LiNO3
All samples placed on white diffusion reflector 288 100 280 155 272
All the sides of the samples except the top were
covered by white diffusion reflector 130 100 121 60 107
Only the crystals were covered by a white
diffusion reflector (all sides except top side) 133 100 84 51 80
Only the crystals were covered by a white
diffusion reflector (just the bottom side) 136 100 88 54 83
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As can be seen from Table 1, the light output
of the composite sample based on the powder
prepared by solid state synthesis with addition
of the mineralizer (ZWO-SSS-LiNO3) is twice as
high as that of the sample synthesized without the
mineralizer (ZWO-SSS).
Table 4 shows that the light output of compos-
ite samples significantly depends on the light col-
lection conditions. The light output of ZWO-SSS-
LiNO3 is comparable with the light output of the
composite based on a crushed ZnWO4 crystal and
is close to a 10×10×2 mm CdWO4 single crystal for
all samples placed on a white diffusion reflector. In
the case when the single crystals were covered with
a white diffusion reflector, the light collection
in single crystal samples improved, and the light
output of ZWO-30-250mm and ZWO-SSS-LiNO3
is comparable to the ZnWO4 single crystal. Also,
in comparison with the single crystal, the com-
posite scintillators demonstrate a good uniformity
of scintillation parameters through the area of the
sample. The results demonstrated in Fig. 10 were
measured using the same light collection condi-
tions for crystals and composite scintillators (all
the sides of the samples except the top ones were
covered by white diffusion reflector, see Fig. 9, b).
As was shown above, a significant increase
in the light output of the composite scintillators
made from crushed single crystals may be caused
by better light collection conditions, which is
obviously characteristic of ZWO-SSS-LiNO3 com-
posites as well.
Conclusions
Research of the scintillation and luminescence
characteristics of flexible composite scintillators
made of micro- and nano-sized ZnWO4 powders ob-
tained by different methods showed the following.
The light output of the composite made of the
ZnWO4 powder obtained by grinding a ZnWO4
bulk crystal is 84—280% of that of the ZnWO4
single crystal and depends on the light collection
conditions. Such a scintillator can be used in vari-
ous X-ray and gamma-ray detectors. Composite
samples of nano-sized ZnWO4 powders obtained
by the hydrothermal-microwave and molten salt
methods are inferior to crushed crystal composite
in terms of their scintillation characteristics.
The solid-state synthesis method using the lith-
ium nitrate mineralizer makes it possible to obtain
a ZnWO4 micron powder with high scintillation
characteristics, bypassing the single crystal growth
stage. Under certain conditions of light collection,
the parameters of a composite scintillator prepared
from such a powder are comparable to those of a
single crystal. Such composite scintillator can be
an alternative to a composite made of a powder
obtained by grinding crystal.
Moreover, the manufactured flexible composite
scintillators have a high uniformity of light output
through the area, which makes them promising for
digital radiography.
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Received 21.05 2018
В. С. ТІНЬКОВА, Г. Г. ЯКУБОВСЬКА1,
І. А. ТУПІЦИНА1, С. Л. АБАШИН2,
Г. Н. ПУЗАН3, С. О. ТРЕТЬЯК1
Україна, м. Харків,
1Інститут сцинтиляційних матеріалів НАН України;
2Національний аерокосмічний університет
«Харківський авіаційний інститут»;
3НТК «Інститут монокристалів» НАН України
E-mail: zvereva@isma.kharkov.ua
ГНУЧКІ КОМПОЗИЦІЙНІ СЦИНТИЛЯТОРИ НА ОСНОВІ
МІКРО- ТА НАНОПОРОШКІВ ZnWO4
Для отримання матеріалів, придатних для використання в сучасних сцинтиляційних детекторах (для
неруйнівного контролю, цифрової радіографії і рентгенографії, a-, b-, g- та нейтронної реєстрації), ве-
дуться пошуки ефективних технологічних методів. Одним з перспективних напрямків досліджень в
цій області є створення композиційних сцинтиляторів на основі мікро- і нанорозмірних кристалічних
порошків. Властивості таких сцинтиляійних порошків істотно залежать від розміру складових їхніх
частинок і морфології, отже, керуючи цими параметрами, можна створити сцинтиляційні детектори з
високими сцинтиляційними характеристиками.
Вольфрамат цинку (ZnWO4) — це перспективний матеріал, який завдяки унікальній комбінації вла-
стивостей може стати успішною заміною CdWO4, що містить токсичний кадмій. У даній роботі
проведені дослідження, спрямовані на пошук ефективного способу отримання порошку ZnWO4 для роз-
робки гнучких композиційних сцинтиляторів з високими функціональними характеристиками, такими
як світловий вихід і рівень післясвітіння.
Досліджували порошки вольфрамату цинку (ZnWO4), синтезовані трьома способами: гідротермальним
з мікрохвильовим нагрівом, розчин-розплавним методом і методом твердофазового синтезу. Отримані
нано- та мікропорошки слугували наповнювачем для створення гнучких композиційних сцинтиляторів. Як
сполучне був використаний силіконовий каучук. Морфологію зразків вивчали за допомогою трансмісійної
та скануючої електронної мікроскопії. Досліджено люмінесцентні характеристики і сцинтиляційні па-
раметри отриманих композитів. Продемонстровано залежність сцинтиляційних параметрів композитів
від морфологічних особливостей нано- та мікрокристалітів ZnWO4.
Світловий вихід композиту з порошку, виготовленого з подрібненого об'ємного кристалу ZnWO4, ста-
новить 84—280% від світлового виходу монокристалла ZnWO4 і залежить від умов збору світла.
DOI: 10.15222/TKEA2019.1-2.40
УДК 539.1.074.3 : 62-492.2 : 546.47'78'21
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49ISSN 2225-5818
MATERIALS OF ELECTRONICS
10
Композиційні зразки з нанорозмірних порошків ZnWO4, отриманих гідротермально-мікрохвильовим і
розчин-розплавним методами, за своїми сцинтиляційними характеристиками поступаються компози-
ту з подрібненого кристала. Твердофазовий метод синтезу з використанням мінералізатора на основі
нітрату літію дозволяє отримувати мікронний порошок ZnWO4 з високим значенням світлового виходу,
минаючи стадію вирощування монокристалу. Параметри композитів на основі такого порошку близькі
до параметрів монокристала вольфрамату кадмію.
Ключові слова: вольфрамат цинку, нанорозмірні кристали, мікророзмірні кристали, композиційні сцин-
тилятори, світловий вихід, рівень післясвітіння.
В. С. ТИНЬКОВА1, А. Г. ЯКУБОВСКАЯ1, И. А. ТУПИЦЫНА1,
С. Л. АБАШИН2, А. Н. ПУЗАН3, С. Е. ТРЕТЬЯК1
Украина, г. Харьков, 1Институт сцинтилляционных материалов НАН Украины;
2Национальный аэрокосмический университет
«Харьковский авиационный институт»;
3НТК «Институт монокристаллов» НАН Украины
E-mail: zvereva@isma.kharkov.ua
ГИБКИЕ КОМПОЗИЦИОННЫЕ СЦИНТИЛЛЯТОРЫ
НА ОСНОВЕ МИКРО- И НАНОПОРОШКОВ ZnWO4
Для получения материалов, пригодных для использования в современных сцинтилляционных детекторах
(для неразрушающего контроля, цифровой радиографии и рентгенографии, a-, b-, g- и нейтронной ре-
гистрации), ведутся поиски эффективных технологических методов. Одним из перспективных направ-
лений исследований в этой области является создание композиционных сцинтилляторов на основе ми-
кро- и наноразмерных кристаллических порошков. Свойства таких сцинтилляционных порошков суще-
ственно зависят от размера составляющих их частиц и морфологии, а значит, управляя этими параме-
трами, можно создать сцинтилляционные детекторы с высокими функциональными характеристиками.
Вольфрамат цинка (ZnWO4) — это перспективный материал, который благодаря уникальной комбина-
ции свойств может быть успешной заменой CdWO4, содержащего токсичный кадмий. В настоящей ра-
боте проведены исследования, направленные на поиск эффективного способа получения порошка ZnWO4
для разработки гибких композиционных сцинтилляторов с высокими функциональными характеристи-
ками, такими как световой выход и уровень послесвечения.
Исследовали порошки вольфрамата цинка (ZnWO4), синтезированные тремя способами: гидротермальным
с микроволновым нагревом, раствор-расплавным методом и методом твердофазного синтеза. Полученные
нано- и микропорошки служили наполнителем для создания гибких композиционных сцинтилляторов. В ка-
честве связующего был использован силиконовый каучук. Морфологию образцов изучали с помощью транс-
миссионной и сканирующей электронной микроскопии. Исследованы люминесцентные характеристики и
сцинтилляционные параметры полученных композитов. Продемонстрирована зависимость сцинтилляци-
онных параметров композитов от морфологических особенностей нано- и микрокристаллитов ZnWO4.
Световой выход композита из порошка, приготовленного из измельченого объемного кристалла ZnWO4,
составляет 84—280% от светового выхода монокристалла ZnWO4 и зависит от условий светособи-
рания. Композиционные образцы из наноразмерных порошков ZnWO4, полученных гидротермально-
микроволновым и раствор-расплавным методами, по своим сцинтилляционным характеристикам усту-
пают композиту из измельченного кристалла. Твердофазный метод синтеза с использованием минерали-
затора на основе нитрата лития позволяет получить микронный порошок ZnWO4 с высоким значением
светового выхода, минуя стадию выращивания монокристалла. Композиты на основе такого порошка об-
ладают параметрами, близкими к параметрам монокристалла вольфрамата кадмия.
Ключевые слова: вольфрамат цинка, наноразмерные кристаллы, микроразмерные кристаллы, композици-
онные сцинтилляторы, световой выход, уровень послесвечения.
Описание статьи для цитирования:
Tinkova V. S., Yakubovskaya A. G., Tupitsyna
I. A., Abashin S. L., Puzan A. N., Tretyak S. O.
Flexible composite scintillators based on ZnWO4
micro- and nanopowders. Техно логия и конструи-
рование в электронной аппаратуре, 2019, № 1-2,
с. 40–49. http://dx.doi.org/10.15222/TKEA2019.1.40
Cite the article as:
Tinkova V. S., Yakubovskaya A. G., Tupitsyna I. A.,
Abashin S. L., Puzan A. N., Tretyak S. O. Flexible
composite scintillators based on ZnWO4 micro-
and nanopowders. Tekhnologiya i Konstruirovanie
v Elektronnoi Apparature, 2019, no. 1-2,
pp. 40–49. http://dx.doi.org/10.15222/TKEA2019.1.40
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