2009 IEEE Nuclear Science Symposium Conference Record
N25-108
Hydrothermal Synthesis and Characterization of nano Gd2O3(Eu) Scintillator for High Resolution X-ray Imaging Application P. Muralidhran, Seung Jun Lee, Bo Kyung Cha, Jong Yul Kim, Chan Kyu Kim, Do Kyung Kim and Gyuseong Cho Abstract–Gd2O3:Eu scintillators with nano-crystalline structures were successfully synthesized through a hydrothermal process and subsequent calcination treatment as a converter for X-ray imaging detectors. In this work, Eu-doped Gd2O3 nanocrystalline powders as a function of calcination temperatures and times were prepared by a hydrothermal process and subsequent calcination in the electrical furnace. Scintillation properties such as luminescent spectra, light intensity and decay time were measured by changing the temperatures and times in heattreatment of as-synthesized nanocrystalline powders. The synthesized samples with different morphology such as nano rods and particles due to calcination temperature were observed. The sample prepared at 1100°C calcination temperature and 5 hour showed the highest light intensity by X-ray excitation. And the scintillator emitted a strong red light at near 611nm under photoand X-ray luminescence for its potential X-ray imaging detector applications.
I. INTRODUCTION X-ray imaging systems have been replacing analog DX-ray imaging systems with conventional X-ray filmIGITAL
screen for radiography applications. Between the direct- and indirect-detection methods for X-ray imaging, indirectdetection type consisted of an X-ray converter (or a scintillator film) and 2D imaging devices are more widely used in medical diagnoses and industrial fields due to its high stability and high performance. Scintillation materials such as terbium doped gadolinium oxysulfide (Gd2O2S:Tb, Gadox), europiumdoped gadolinium oxide(Gd2O3:Eu) and CsI:Tl screen with columnar structure are commonly used because of their high luminescence efficiency and emission wavelength(visible light region) well matching to silicon sensors such as a-Si:H panel detector, CCD and CMOS type imaging devices [1], [2]. However, scintillators with higher sensitivity and spatial resolution are still required for X-ray imaging detector development. It is reported that nano-sized phosphor particle have different electrical, optical and structural properties due to the quantum size effect, surface and interface effects. This work was supported in part by 2009 Nuclear R&D program of MEST (Ministry of Education, Science and Technology), Korea through KOSEF (20090062198). Bo Kyung Cha, Jong Yul Kim, Chan Kyu Kim and Gyuseong Cho are with the Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea 305-701 (telephone: 8242-350-3861, e-mail:
[email protected]). P. Muralidhran, Seung Jun Lee and Do Kyung Kim are with the Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea 305-701.
9781-4244-3962-1/09/$25.00 ©2009 IEEE
Furthermore, it is known that X-ray absorption efficiency due to a higher packing density and spatial resolution due to the reduced light spreading using the nanocrystalline phosphor could be improved. In this work, Gd2O3:Eu scintillators with nanocrystalline structures were synthesized through a hydrothermal method and subsequent calcination process with different temperatures and times. And the microstructures such as particle size, morphology and crystal structures as a function of various calcination temperatures and times were observed. Moreover, their scintillation properties such as luminescent spectra and light intensity by photo- and X-ray excitation were investigated [3], [4]. II. MATERIALS AND METHODS A. Synthesis of the Gd2O3(Eu) Scintillators A simple hydrothermal process was carried out to prepare 5mol% Eu-doped nanocrystalline Gd2O3 powders. 4.287g of Gd(NO3)3 was added to 20ml of dist. water and 0.2140g of Eu(NO3)3 was added to the above solution. The solution was made up to 50 ml by addition of water. 40 ml of 1 M NaOH solution was then added to the above solution and made up the solution to 100 ml by addition of 10ml water. The precipitate solution was mixed well upon continuous stirring. After 15 min. 80 ml of the solution were poured into the Teflon jar and placed in an autoclave and reaction was carried out at 180 C for 24 h. The white precipitate was washed with dist. water and ethanol for 3 times and dried at 90 C for 12 h. Thus obtained sample was subsequently calcined at different temperatures with 600-1400C and times with 1-10hours in electrical furnace [5]. B. Measurement of Microstructures and Crystal Structures of the Gd2O3(Eu) Scintillators The microstructures such as particle sizes, morphology and the existing phase of the synthesized Gd2O3:Eu with various calcination temperatures and times were performed by FESEM (JEM-2100F HR) and high resolution X-ray diffraction(Ultima IV, RIGAKU) with an analysis range 2 of 20~90¶ respectively. And the particle sizes of the prepared Gd2O3:Eu samples were also measured by the DeybyeScherrer equation using the diffraction peak full-width at halfmaximum (FWHM).
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C. Measurement of Photo-Luminescence and Light Output by X-ray Excitation Photoluminescence (PL) and decay time were measured by means of a Czerny-Turner spectrometer and intensified charge coupled device camera using a Nd:YAG laser with 266nm excitation source. A relative light output of the synthesized nanocrystalline Gd2O3(Eu) powders was measured using a lens-coupled CCD camera (Andor DV-434) and X-ray source (LISTEM, BRS-2) with 4.3mm spot size and inherent 0.8mm Al filter. The light intensity was acquired by measuring an averaged pixel value over region of interest (ROI) in obtained X-ray images at same X-ray exposure condition. III. RESULTS AND DISCUSSION A. Microstructures of the Gd2O3(Eu) Scintillators The morphology and particle sizes of the synthesized Gd2O3(Eu) scintillator powders with different calcination temperatures ranging from 700 to 1400C and times from 1 to 10 hours at a constant 1100 C calcination temperature are shown in Fig. 1 and 2 respectively by SEM. As the calcination temperature increases, the average diameters of the powders were considerably increased from 20nm to 1»m. The nano particle sizes of Gd2O3(Eu) scintillator were maintained until 1200C temperature. But, particle sizes of the powders calcinated over 1300C temperature showed the micron sizes in a hydrothermal method. The morphology with nanorods ranging from 700 to 1000C temperatures was observed and its morphology over 1100C was changed to nano-and microparticles. As calcination time at 1100C temperature increases, particle size was largely increased. However, the particle size was maintained below 200nm.
B. Crystal structures of the Gd2O3(Eu) Scintillators The XRD peak patterns of the synthesized Gd2O3(Eu) scintillator powders with various calcination temperatures ranging 600-1400C and 1-10 hour calcinations times at a constant 1100C were shown in Fig. 3 and 4 respectively. As calcination temperature from 600 to1200C increases, the diffraction peak width was reduced and showed sharper pattern peaks. As-synthesized powder has XRD peak patterns of Gd(OH)3 structure Fig. 3. X-ray peaks at the powders of Gd2O3(Eu) calcinated at 600-1200C has (211), (222), (400), (440), and (622) and are in agreement with cubic crystal structures of Gd2O3(JCPDF cards 00-012-0797). The phase transformation from the cubic to monoclinic structure was discovered at 1300 and 1400temperature and their peaks were corresponding to the monoclinic phase (JCPDF cards 00043-1015). Although calcination time from 1 to 10 hours at 1100C temperature increases, cubic phase of Gd2O3 was not changed. As calcination time increases, the diffraction peak width was also decreased and showed sharper pattern peaks [5].
Fig. 3. XRD of synthesized Gd2O3:Eu scintillators with different calcination temperatures.
Fig. 1. SEM images of the synthesized Gd2O3(Eu) scintillator powders with different calcination temperatures; (a)700, (b)800, (c)900, (d)1000, (e) 1100, (f)1200, (g)1300 and (h)1400 C.
Fig. 4. XRD of synthesized Gd2O3:Eu scintillators with different calcination times.
Fig. 2. SEM images of the synthesized Gd2O3(Eu) scintillator powders with different calcination times; (a)1, (b)3, (c)5, (d)7 and (e)10 hour.
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C. Photoluminescence Excitation
and
Light
Output
by
X-ray
The PL (photo-luminescence) intensities and emission spectra as a function of calcination temperatures are displayed in Fig. 5. The PL intensities of samples were increased rapidly as the temperature increases until 1200ଇ. However, the intensities were decreased above a 1300ଇ temperature. Moreover, the main emission peak of the Gd2O3:Eu scintillator with cubic structure was observed at 611nm(5D0˧7F2) wavelength, which correspond to a typical red emission transition of Eu3+. The photoluminescence of the powders with the monoclinic phase calcinated at 1300 and 1400ଇ showed a strong emission peak at 623nm wavelength. And the decay curves of the emitted photons of the Gd2O3(Eu) scintillator with various calcination temperatures after excitation at 266nm are shown in Fig. 6. The decay times with 0.5-1.2ms as a function of calcination temperatures were measured. And the light intensities of the Gd2O3:Eu scintillator with various calcination temperatures and times were measured by luminescence under X-ray source exposure with 80kVp and 30mAs beam current. The highest light intensity by X-ray excitation was observed at 1100ଇ among various temperatures as shown in Fig. 7. And the Gd2O3:Eu scintillator calcinated at 1100ଇ temperature and 5 hour time showed the highest light output as shown in Fig. 8 [6].
Fig. 6. Decay curves of the synthesized Gd2O3:Eu scintillators with different calcination temperatures.
Fig. 7. Light output of the synthesized Gd2O3:Eu scintillators with different calcination temperatures.
Fig. 5. PL spectrum of the synthesized Gd2O3:Eu scintillators with different calcination temperatures. Fig. 8. Light output of the synthesized Gd2O3:Eu scintillators with different calcination times.
IV. CONCLUSIONS AND FUTURE WORKS Eu-doped Gd2O3(Gd2O3:Eu) scintillators with nanocrystalline structure were synthesized through a hydrothermal method and subsequent calcination process for X-ray imaging detectors. In this work, the scintillators with average 20nm to 1μm particle size were synthesized according to various calcination temperatures ranging from 600 to 1400ଇ and times. The morphology of Gd2O3:Eu powder with
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nanorods until 700-1000ଇ calcination temperature was observed. The Gd2O3:Eu powder with nano particles over 1100ଇ was slowly appeared. The phase transformation from cubic to monoclinic structure was discovered at 1300ଇ calcination temperature. When the Gd2O3:Eu scintillator were excited by UV light of 266nm, dominant emission peak of samples with cubic structure was showed at 611nm, on the other hands, the main peak of those with monoclinic structure was observed at 623nm wavelength. The particle size and luminescence intensity of synthesized Gd2O3(Eu) powders were greatly influenced by calcination temperatures. As calcination temperature increases, the particle sizes of Gd2O3(Eu) powder with nanocrystalline structures and the luminescent intensity were considerably increased. The highest light intensity by photo- and X-ray luminescence was showed at 1200 and 1100ଇ calcination temperature respectively. In the near future, nanocrytalline-Gd2O3:Eu scintillator, which was synthesized through a hydrothermal method and subsequent heat-treatment at 1100ଇ and 5h will be used as a converter screen type for X-ray imaging detectors with high light output and spatial resolution. And X-ray imaging performance of the nanocrytalline-Gd2O3:Eu scintillator screen will also be investigated. ACKNOWLEDGMENT This works was supported by 2009 Nuclear R&D program of MEST (Ministry of Education, Science and Technology), Korea through KOSEF (20090062198). REFERENCES [1] [2]
[3]
[4]
[5]
[6]
Martin Nikl, "Scintillation detectors for x-rays," Meas. Sci. Technol., 17 R37-R54, February 2006. John Yorkston, "Recent developments in digital radiography detectors," Nuclear Instruments and Methods in Physics Research A 580, pp. 974985, June 2007. So-yeong Kim, Ji-koon Park, Sang-sik Kang, Byung-youl Cha, Sung-ho Cho, Jung-wook Shin, Dae-woong Son, Sang-hee Nam, Nuclear Instruments and Methods in Physics Research A 576, pp. 70-74, February 2007. Muralidhar Mupparapu, Rameshwar N. Bhargava, Satish Mullick, Steven R. Singer, Nikhil Taskar, Aleksey Yekimov, “Development and application of a novel nanophosphor scintillator for a low-dose, highresolution digital X-ray imaging system”, International Congress Series 1281, pp. 1256-1261, 2005. Chengkang Chang, Fumiko Kimura, Tsunehisa Kimura, Hitoshi Wada, “Preparation and characterization of rod-like Eu:Gd2O3 phosphor through a hydrothermal routine,” Materials Letters, 59, PP. 1037-1041, 2005. Guixia Liu, Guangyan Hong, Jinxian Wang, Xiangting Dong, “Hydrothermal synthesis of spherical and hollow Gd2O3:Eu3+ phosphors”, Journal of Alloys and Compounds, 432, pp. 200-204, 2007.
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