Flexible Gd₂O₂S:Tb scintillators pixelated with polyethylene microstructures for digital x-ray image sensors

Abstract

Flexible scintillators for digital x-ray image sensors were designed, fabricated and characterized. In these scintillaotrs, terbium-doped gadolinium oxysulfide (Gd 2 O 2 S:Tb) scintillator pixels were embedded into a polyethylene (PE) substrate. To evaluate the difference in the spatial resolution according to the pixel size, we designed three scintillators with pixels of different pitch sizes: 50 μm pitch size (P50), 100 μm pitch size (P100) and 200 μm pitch size (P200). Because of the high flexibility and good formability, polyethylene was used as the substrate of the scintillator. To fabricate nickel micromolds with high-aspect-ratio microstructures, two microfabrication techniques were employed: silicon dry-etching using a deep reactive ion etching (DRIE) process and nickel electroforming. The pixelated PE microstructures were fabricated by a hot embossing process. Because the solution-type Gd 2 O 2 S:Tb precursor can be handled at room temperature, Gd 2 O 2 S:Tb was used as the scintillator material. The measured sensitivities of the P50 and P100 models were, respectively, about 65% and 97% of that of the P200 model. The lower sensitivity values of the models with a small pitch size were due to two factors, such as the different pixel heights and the different fill factors. Because a scintillator with a small pixel size has a low fill factor, the sensitivity of the scintillator decreases as the pixel size decreases. The fill factors of the P50, P100 and P200 models were 36%, 49% and 56.25%, respectively. On the other hand, the spatial resolution of the scintillator increases as the pixel size decreases. Therefore, P50 gave the best spatial resolution among the designed models. The spatial frequency at 10% of the modulation transfer function (MTF) with P50 was 13.5 mm −1 , while that with P200 was 10.0 mm −1 . The resolution pattern and the tooth x-ray images obtained from a scintillator with a smaller pixel size was also clearer than that obtained from a scintillator with a larger pixel size. PE-based flexible Gd 2 O 2 S:Tb scintillators can be utilized directly in flexible x-ray image sensors.

Shining Emitter in a Stable Host: Design of Halide Perovskite Scintillators for X-ray Imaging from Commercial Concept

“…That is where the “emitter-in-matrix” design principle, refined from commercial scintillators, takes effect. Usually rare-earth dopants as emitting centers are incorporated into a crystal host to tackle the contradiction mentioned above, thereby producing the most widely used scintillators including CsI:Tl, NaI:Tl, Gd 2 O 2 S:Tb, LaBr 3 :Ce, LaCl 3 :Ce, CaI 2 :Eu, CaF 2 :Eu, and so on. − Alternatively, these years have witnessed the prosperous development of fluorescent nanomaterials with low-temperature solution synthesis, higher quantum yields (QYs), narrower line width, and tunable emissions to replace rare-earth emitters in next-generation scintillation techniques. − However, after developing so many kinds of nanomaterials, they have yet to be applied in the market to date. The market is the most honest referee to indicate the commercial feasibility, and the failure of nanomaterials in scintillators can be ascribed to their rapid degradation upon irradiation, , as well as the easy formation of nonradiative recombination paths to compromise the optical properties …”

Microdome-gooved Gd_2O_2S:Tb scintillator for flexible and high resolution digital radiography

“…1(b), the converted visible light in the conventional scintillator scatters in all directions, thereby degrading spatial resolution. Several methods have been developed to suppress spreading of the converted visible light, including columnar-structured cesium iodide (CsI:Tl) [1], pixel-structured CsI:Tl [2,3], and pixel-structured gadolinium oxysulfide (Gd 2 O 2 S:Tb) [4][5][6][7] (hereafter, Gd 2 O 2 S:Tb and CsI:Tl are referred to as GOS and CsI, respectively). Silicon-based U-grooved structures with thin walls have been produced for pixel-structured scintillators using microelectromechanical system (MEMS) fabrication technology [2,3].…”

“…In contrast to CsI, GOSbased scintillators are very flexible, because GOS is generally mixed with organic materials. Polymer-based U-grooved scintillators have also been developed in order to exploit the flexibility of polymers [7]. Although U-grooved polymer structures are a good prototype for flexible scintillators, they have two crucial drawbacks: low fill factor and a difficult fabrication process.…”

Size and optical versatility in rare earth oxysulfide photonic materials

“…Regarding practical applications, additional features are desired for scintillator devices, e.g., fast response (short decay times), high chemical and radiation stability, device versatility, and high energy resolution, i.e., the ability to discriminate between different radiation energies [46]. The intrinsic resolution of a scintillator is defined by the materials' inherent characteristics.…”

“…Scintillator materials such as Gd2O2S:Tb 3+ and Gd2O2S:Pr 3+ have been deeply investigated since they exhibit the main features necessary to enable good absorption of X-rays beams, such as the presence of heavy atoms (Ln as host and dopants), high material density, and high stability against ionizing radiations. Nowadays, these materials are used as scintillators in X-ray Computed Tomography (CT), Single-Photon Emission Computed Tomography (SPECT), and Positron Emitting Tomography (PET) [12,43,46].…”