Hydrothermal synthesis of CdWO4 for scintillator-polymer composite films development
Introduction
Scintillator compounds are continuously investigated for improving their potential applications which include medical image detectors, dosimetry and industrial inspection. Besides the features of efficiency, decay time and chemical stability, it is also important to achieve low costs of production especially when large areas need to be covered [1], [2]. In this sense, systems based on inorganic particles embedded in polymeric matrix are shown to be promising since they can combine the mechanical features of polymers with the optical properties of scintillators. These organic/inorganic composites have thus aroused great interest in recent years as inexpensive and efficient detectors for ionizing radiation [3], [4], [5], [6].
The use of a material with high effective atomic number Z will increase the stopping power, that is, the absorption of high energy radiation by the composite in comparison with the polymer without such particles [7], [8]. In many cases, energy transfer between these elements take place, with the luminescent properties of the composite determined by these processes. On the other hand, one of the main issues that need further attention is the control of the particles dispersion within the polymeric matrix. Particle clusters can act as scattering centres, which compromise the spatial resolution of the detectors, whereas low amounts of scintillator result in decrease of the luminescence efficiency [8], [9].
Cadmium tungstate (CdWO4) is a well-known scintillator due to its useful features such as high density (7.9 g/cm3), large Z (61.2) and efficient scintillation output (~40% of NaI:Tl). Owing to the difficulties to obtain CdWO4 as single crystals, many other synthesis routes have been developed to produce polycrystalline samples including sol-gel, sonochemical and hydrothermal [10], [11], [12], [13]. Up to our knowledge, however, few reports have explored the ability to prepare composites loaded with this compound [14]. The search for new scintillating films is relevant since the convenience of using as the primary radiation sensor in many detection systems, including synchrotron radiation facilities [15], [16].
In this work, scintillator composites have been prepared using CdWO4 and polystyrene (PS). The advantages of using PS consist on its low cost, good resistance to thermal and light deterioration, flexibility and high transparency over a large spectra range [1], [17]. The synthesis of CdWO4 powder employed a simple microwave-assisted hydrothermal method, which allowed the formation of single crystalline phase at temperatures as low as 100 °C. Our approach involves the surface modification of the particles in order to improve their compatibility with the polymeric matrix and achieve a higher homogeneity of the composite films [18].
Section snippets
Material and methods
For the synthesis of CdWO4 powder, a microwave-assisted hydrothermal method was developed. In a typical procedure, stoichiometric amounts of CdO (Vetec, 99.5%) and WO3 (Fluka, 99.9%) were homogenized in an agate mortar and placed into a Teflon autoclave filled with 100 ml of distilled water. Then, the autoclave was sealed and placed in the microwave system (Brazilian patent 2008-PI0801233-4) with frequency of 2.45 GHz and maximum power of 800 W. Reactions were conducted at 100 °C and 120 °C
Results and discussion
Fig. 1 shows the powder XRD of the samples prepared using pH 7.0, 8.0 and 9.0, at the temperature of 120 °C. One can observe that the oxide precursors reacted under hydrothermal conditions and CdWO4 was obtained at significantly lower temperature and faster than in the solid state synthesis [21], [22]. The pattern of the sample obtained at pH 7.0 presented a small amount of WO3 as secondary phase, due to Cd losses during the synthesis. It could be compensated using CdO excess to the
Conclusions
The single crystalline phase of CdWO4 obtained using oxide precursors under microwave-assisted hydrothermal conditions has been demonstrated for the first time. This low-cost method involves low temperatures and short synthesis times, and thus it was suitable to produce the scintillator powder employed as load of composite films. The surface modification of CdWO4 particles by stearic acid was efficient to improve the dispersion within the polystyrene matrix. Microtomography scans have shown
Acknowledgments
This work has been supported by the Brazilian funding agencies CNPq, CAPES, FINEP and FAPITEC. The authors are also grateful to the Brazilian Synchrotron Light Laboratory (LNLS) and the beamlines staff for helping with proposals TGM#20170460 and IMX#20160751.
References (35)
- et al.
Luminescent and kinetic properties of the polystyrene composites based on BaF2 nanoparticles
Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrom. Detect. Assoc. Equip.
(2016) - et al.
X-ray excited luminescence of polystyrene composites loaded with SrF2 nanoparticles
Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrom. Detect. Assoc. Equip.
(2017) - et al.
Low-temperature synthesis of CdWO4 nanorods via a hydrothermal method
Ceram. Int.
(2007) - et al.
Preparation and optimization of CdWO4-polymer nano-composite film as an alpha particle counter
Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrom. Detect. Assoc. Equip.
(2017) - et al.
Bismuth germanate films prepared by Pechini method
Opt. Mater.
(2010) - et al.
Preparation and characterization of BaSO4/poly(ethylene terephthalate) nanocomposites, Colloids
Surf. A Physicochem. Eng. Asp.
(2011) - et al.
Thermally stimulated luminescence of polycrystalline CdWO4 at low temperatures
J. Lumin.
(2011) - et al.
Synthesis of nano and micro crystals of Cd(OH)2 and CdO in the shape of hexagonal sheets and rods
Appl. Surf. Sci.
(2007) Microwave-assisted synthesis of CdWO4 by solid-state metathetic reaction
Mater. Chem. Phys.
(2012)- et al.
Photoluminescence study of cadmium tungstate crystals
J. Phys. Chem. Solids
(2000)
Gd2O3:Eu3+/PPO/POPOP/PS composites for digital imaging radiation detectors
Appl. Phys. A
X-ray imaging with scintillator-sensitized hybrid organic photodetectors
Nat. Photonics
Facile single-precursor synthesis and surface modification of hafnium oxide nanoparticles for nanocomposite γ-ray scintillators
Adv. Funct. Mater.
Optical properties of hybrid composites based on highly luminescent CdS nanocrystals in polymer
Nanotechnology
Cathodoluminescence characterization of polystyrene-BaZrO3 hybrid composites
Low Temp. Phys.
X-ray excited luminescence of polystyrene-based scintillator loaded with LaPO4-Pr nanoparticles
J. Appl. Phys.
Nanoparticle polymer composites: where two small worlds meet
Science (80)
Cited by (17)
Development of flexible scintillation sensors based on Ag and Gd doped CdWO<inf>4</inf> nanocomposites
2022, Applied Radiation and IsotopesOne-step synthesis of YF<inf>3</inf>:Nd rod-like particles for contactless luminescent thermometers
2022, Optical MaterialsCitation Excerpt :In this sense, microwave-assisted hydrothermal method combines the advantages of fast heating and high-pressure reaction. As a result, nanocrystals are produced in shorter times and at lower temperatures, if compared to those produced using conventional synthesis [26–32]. Furthermore, the microwave uniform heating promotes a better control of the particle size and morphology [33].
Development of CdWO<inf>4</inf>-polystyrene scintillator composites for X-ray detection in imaging systems
2022, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentZinc oxide/polystyrene composite based scintillator for alpha particle monitoring
2021, Materials Science in Semiconductor ProcessingCitation Excerpt :Polyester, Epoxy, PDMS, polystyrene (PS), and PVT are commonly used base materials for the preparation of such composites [9,10]. Among these, polystyrene is widely used for preparing nanocomposite scintillators by hosting many luminescent materials such as metal oxides and halides, etc [11] [–] [17]. Zinc oxide is a wide and direct bandgap semiconductor material and used in many applications, including optical and electronic applications.