Scintillator Films Research Articles

Scaling-induced enhancement of X-ray luminescence in CsI(Na) crystals

We report on the diameter dependence luminescence property of CsI(Na) crystals under X-ray excitation. When CsI(Na) crystal diameter decreases to nano-scale, the X-ray excited luminescence decay time is speeding up from ∼600 ns to ∼10 ns and 420 nm Na-related cathodeluminescence is affected drastically. The reason is confirmed that diameter reduction leads surface effect to accelerate the excitons' quenching. These measurement results identify a critical distinguished boundary ∼20 μm) of crystal diameter, which provide a new way to potential application of CsI(Na) crystals in the development of fast X-ray and gamma scintillator film detectors with large area.

Transparent lithiated polymer films for thermal neutron detection

Novel water-soluble 6Li loaded copolymer scintillation films have been designed and fabricated to detect thermal neutrons. Styrene and maleic anhydride were copolymerized to form an alternating copolymer, then the anhydride functionality was hydrolyzed using 6Li hydroxide. The resulting poly(styrene-co-lithium maleate) was mixed with salicylic acid as a fluor and cast as a thin film from water. The maximum 6Li loading obtained that resulted in a transparent film was 4.36% by mass (6Li to polymer). The optimum fluorescence output was obtained for 11.7% salicylic acid by mass, presumably in the form of lithium salicylate, resulting in an optimum film containing 3.85% by mass of 6Li. A facile and robust synthesis method, film fabrication protocol, photoluminescence results, and scintillation responses are reported herein.

Performance of columnar CsI(Tl) scintillation films prepared on special pre-deposited layers

CsI(Tl) scintillation films are widely used for X-ray imaging because their micro-columnar structure can decrease the lateral spreading of scintillating light. But the CsI(Tl) films usually show a disorder structure near the interface of the substrate and film. In this work, CsI(Tl) scintillation films were prepared on the substrates covered by a special pre-deposited CsI layer. This pre-deposited layer shows the morphology of isolated islands with uniform distribution which is caused by solid-state dewetting. The inter-island distance is determined by the initial film thickness. It is found that the columns of the CsI(Tl) films deposited on the pre-deposited layer grew from bottom to the top without disorder. The column diameter is determined by the inter-island distance. The XRD patterns of the films show only [100] preferred orientation which was the same as those of the pre-deposited layers. The performances of the films including light output and spatial resolution have been improved when the films are prepared on this kind of special pre-deposited layers.

High efficiency microcolumnar Lu2O3:Eu scintillator thin film for hard X-ray microtomography

We have developed microstructured Lu2O3:Eu scintillator films capable of providing spatial resolution on the order of micrometers for hard X-ray imaging. In addition to their extraordinary resolution, Lu2O3:Eu films simultaneously provide high absorption efficiency for 20 to 100 keV X-rays, and bright 610 nm emission, with intensity rivalling that of the brightest known scintillators. At present, high spatial resolution of such a magnitude is achieved using ultra-thin scintillators measuring only about 1 to 5 μm in thickness, which limits absorption efficiency to ~3% for 12 keV X-rays and less than 0.1% for 20 to 100 keV X-rays, resulting in excessive measurement time and exposure to the specimen. Lu2O3:Eu would significantly improve that (99.9% @12 keV and 30% @ 70 keV). Important properties and features of our Lu2O3:Eu scintillator material, fabricated by our electron-beam physical vapour deposition (EB-PVD) process, combines superior density of 9.5 g/cm3, microcolumnar structure emitting 48000 photons/MeV whose wavelength is an ideal match for the underlying CCD detector array. We grew thin films measuring 5–50μm in thickness as well as covering areas up to 5 × 5 cm2 which can be a suitable basis for microtomography, digital radiography as well as CT and hard X-ray Micro-Tomography (XMT).

Large-Area Crystalline Microcolumnar LaBr$_{3}$:Ce for High-Resolution Gamma Ray Imaging

Novel fabrication methods for cost-effective and large-volume production of important lanthanide halide scintillators are currently being explored. Here we report on the growth of LaBr :Ce scintillator films in a novel light conserving morphology known as Crystalline Microcolumnar StructureTM (CMSTM), using Hot Wall Evaporation (HWE) technique. This method produces specimens which preserve the response uniformity over the area of the film, and low attenuation of light throughout its thickness. Using this approach, we have produced LaBr :Ce film samples measuring 3-7 cm in diameter and approaching 2 cm in thickness, with densely packed microcolumns averaging ~15 μm in diameter. Some of these films show bright light emissions compared to their crystalline counterparts, demonstrating energy resolution of ~9.4% at 122 keV ( Co emission) and uniformity in light response across the area of the scintillator. Imaging data acquired using the University of Arizona Bazooka SPECT detector incorporating our CMS LaBr :Ce film demonstrated m spatial resolution ~138 μm at 122 keV in single-photon counting imaging mode. This technique permits fabrication of thick films that can simultaneously provide the high absorption efficiency and high spatial resolution required for small-animal SPECT imaging and other medical and non-medical applications.

The Luminescence of a CuI Film Scintillator Controlled by a Distributed Bragg Reflector

We investigate the emission properties of CuI film scintillators and the effect of distributed Bragg reflectors. The free-exciton emission and the donor-acceptor pair emission from the CuI thin film with the peak wavelengths of 410 nm and 420 nm are observed. However, for the two emission bands, the distributed Bragg reflector reflection results in different enhancements, which is interpreted by the varying transmittance with wavelength. Angle-dependence of emission profile is decided by the transmittance and DBR reflection, which may be useful in scintillation detection applications.

Preparation of CsI(Tl) Scintillation Film by RF Magnetron Sputter Method and its Structural and Optical Characterization

Thallium-doped cesium iodide CsI(Tl) scintillation film has been manufactured by radio frequency (RF) magnetron sputter method onto the quartz glass substrates. The X-ray diffraction (XRD) pattern of the film shows preferable growth of the crystalline film in the (200) orientation. The optical and scintillation properties of CsI(Tl) film were investigated, including photoluminescence excitation (PLE), photoluminescence (PL), X-ray excited luminescence (XEL) spectra and decay curve. The main emission peak at about 2.28 eV is related to the radiative relaxation from the strong-off configuration of localized excitons around Tl+ ions. Under UV excitation, the 2.28 eV emission of CsI(Tl) film presents a single exponential decay with 545 ns.

Enhanced luminescence of CuI thin film scintillator by reducing Fresnel reflection

CuI thin film scintillator has potential applications in radiation detection systems due to its fast component of luminescence. Severe Fresnel reflection due to its large refractive index decreases its external quantum efficiency. In this article, we design an antireflection coating of SiO2 to efficiently eliminate Fresnel reflection and thus improve luminescence intensity. The optimal thickness of coating aimed at the maximum transmission for the omni-directional integration is obtained. The reduced Fresnel reflection by the antireflection coating is based upon the gradient-index and the interference effect. The luminescence intensity with an antireflection coating is increased by 20% at the emission peak wavelength.

Development of a single-shot-imaging thin film for an online Thomson parabola spectrometer

A single-shot-imaging thin scintillator film was developed for an online Thomson parabola (TP) spectrometer and the first analysis of laser accelerated ions, using the online TP spectrometer, was demonstrated at the JAEA-Kansai Advanced Relativistic Engineering Laser System (J-KAREN). An energy spectrum of ~4.0 MeV protons is obtained using only this imaging film without the need of a microchannel plate that is typically utilized in online ion analyses. A general-purpose Monte Carlo particle and heavy ion-transport code system, which consists of various quantum dynamics models, was used for the prediction of the luminescent properties of the scintillator. The simulation can reasonably predict not only the ion trajectories detected by the spectrometer, but also luminescence properties.

Bio-mimetic integrated surface nano structures for medical imaging scintillation materials

ABSTRACTWe have improved bio-inspired Moth eye nanostructures to enhance the scintillator materials external quantum efficiency significantly. As a proof of concept, we have demonstrated very high light output efficiency enhancement for Lu2SiO5:Ce3+ (LSO:Ce) film in large area. The X-ray mammographic instrument was employed to demonstrate the light output enhancement of the Lu2SiO5:Ce thin film with bio-inspired Moth eye-like nano photonic structures. Our work could be extended to other thin film scintillator materials and is promising to achieve lower patient dose, higher resolution image of human organs and even smaller scale medical imaging.

Compensational scintillation detector with a flat energy response for flash X-ray measurements

To measure the intensity of flash X-ray sources directly, a novel scintillation detector with a fast time response and flat energy response is developed by combining film scintillators of doped ZnO crystal and fast organic scintillator together. Through compensation design, the dual-scintillator detector (DSD) achieved a flat energy response to X-rays from tens of keV to several MeV, and sub-nanosecond time response by coupling to ultrafast photo-electronic devices. A prototype detector was fabricated according to the theoretical design; it employed ZnO:In and EJ228 with thicknesses of 0.3 mm and 0.1 mm, respectively. The energy response of this detector was tested on monoenergetic X-ray and γ-ray sources. The detector performs very well with a sensitivity fluctuation below 5% for 8 discrete energy points within the 40-250 keV energy region and for other energies of 662 keV and 1.25 MeV as well, showing good accordance with the theoretical design. Additionally, the detector works properly for the application to the flash X-ray radiation field absolute intensity measurement. This DSD may be very useful for the diagnosis of time-resolved dynamic physical processes of flash X-ray sources without knowing the exact energy spectrum.

New High Stopping Power Thin Scintillators Based on ${\rm Lu}_{2}{\rm O}_{3}$ and ${\rm Lu}_{3}{\rm Ga}_{5-{\rm x}}{\rm In}_{\rm x}{\rm O}_{12}$ for High Resolution X-ray Imaging

X-ray computed tomography devices and X-ray diffraction techniques are powerful tools: the former provide volumetric data of samples during a non-destructive examination for biology and material science, and the latter measure grain orientation and strain, as well as crystalline phase identification and structure refinement. Today, the European Synchrotron Radiation Facility (ESRF) provides increasingly higher energy beams, up to 150 keV combined with higher brilliance (1013 X-ray photons/sec). This means that detectors suffer from low X-ray absorption at high spatial resolution (1-10 μm) and from radiation damage in tomography and diffraction applications. In addition, more and more experiments in medicine require the absorbed dose by the sample to be reduced. In this context, more efficient scintillators are developed and evaluated at the ESRF. In order to perform sub-micrometer and micrometer resolution imaging scintillators 1 μm to 500 μm thin are required. Single Crystal Film scintillators (SCF), 1 μm to 100 μm can be obtained via Liquid Phase Epitaxy for sub-micrometer resolution. Transparent ceramics, 100 μm to 500 μm thick are promising candidates for X-ray imaging requiring high X-ray absorption and good contrast with micrometer resolution. Commonly available scintillators, such as CdWO4 and YAG:Ce suffer from low efficiency, therefore new scintillators with higher light yield and stopping-power are required. A first test was carried out to evaluate an Europium doped Lutetium Oxide ceramic for micrometer resolution and new SCFs of Lu3Ga5-xInxO12:Eu for sub-micrometer resolution are investigated. Performance of Lu2O3 and LuInGG, i.e absorption, light yield, afterglow, spatial resolution will be presented and compared to standard screens (YAG, GGG). First results will be illustrated with X-ray images and will demonstrate the absorption efficiency improvement at high spatial resolution.

Scintillators Based on ${\hbox{CdWO}}_{4}$ and ${\hbox{CdWO}}_{4}\!\!:\!\!{\hbox{Bi}}$ Single Crystalline Films

This research is directed on creating by liquid phase epitaxy the single crystalline film scintillators based on undoped and Bi doped CdWO4 compounds as well as the phoswich detector based on “CdWO4:Bi or CdWO4 films/CdWO4 or CdWO4:Bi crystals” epitaxial structures. The luminescent and scintillation properties of the undoped and Bi3+ doped (in a concentration range of 0.04-0.25 at. %) CdWO4 films, grown by LPE method from Na2WO4 flux, were compared with the properties of CdWO4 bulk crystal analogs, grown from melts by the Czochralski method. Using the traditional luminescence spectroscopy and the luminescence spectroscopy under excitation by pulsed synchrotron radiation with energy in the fundamental absorption range of CdWO4 host, we have also examined the nature of different emission centers and studied energy transfer processes from tungstate hosts to Bi3+ ions and defect centers in CdWO4 and CdWO4:Bi films and their crystal analogs.

Polyester Composite Thermal Neutron Scintillation Films

Novel $^{6}{\rm Li}$ -loaded polyester scintillation films have been designed and fabricated to detect thermal neutrons. Lithium fluoride crystals containing enriched $^{6}{\rm Li}$ were synthesized and integrated into polyethylene naphthalate polyester matrix containing appropriate luminescent molecules. Thermal neutron capture by $^{6}{\rm Li}$ ions produces charged particles with kinetic energy sufficient to ionize and subsequently excite the components of the polymeric matrix. This energy is transferred to secondary luminescent molecules, which produce net radioluminescence responses detectable by a photomultiplier tube. Design, production and characterization of these scintillation films are discussed herein. The films due to their thinness $( and low atomic number components have low susceptibility to gamma induced scintillation and thus are effective discriminators for thermal neutrons.

Giant light extraction enhancement of medical imaging scintillation materials using biologically inspired integrated nanostructures

We have utilized biologically inspired (bio-inspired), moth-eye nanostructures and further improved this biomimetic structure to enhance the scintillator materials external quantum efficiency significantly. As a proof of concept, we have demonstrated very high light output efficiency enhancement for Lu(2)SiO(5):Ce(3+) (LSO:Ce) film in large area, the X-ray mammographic instrument was employed to demonstrate the light output enhancement of the Lu(2)SiO(5):Ce thin film with biologically inspired (bio-inspired) moth-eye-like nanophotonic structures. Our work could be extended to other thin film scintillator materials and is promising to achieve lower patient dose, higher resolution images of human organs and even smaller scale medical imaging.

Characterization of indirect X-ray imaging detector based on nanocrystalline gadolinium oxide scintillators for high-resolution imaging application

Nanocrystalline Gd2O3:Eu scintillating powders were successfully synthesized through a co-precipitation process for X-ray imaging detector applications. In this work, as-synthesized sample was further calcinated at different temperature, time with 1–10h and doped-Eu3+ concentration with 1–10mol% in the electrical furnace. The characterization such as the crystal structures and microstructure of Gd2O3:Eu scintillator were measured by XRD and SEM experiment. The phase transition from cubic to monoclinic structure was observed at 1300°C calcination temperature. Dominant emission peak of sample with cubic structure was appeared at 611nm under 266nm UV light excitation. After scintillation properties of synthesized Gd2O3:Eu scintillator were investigated, Gd2O3:Eu scintillating films with different thickness was fabricated onto glass substrate by a screen printing method. And then X-ray imaging performance in terms of the light response to X-ray exposure dose, signal-to-noise ratio (SNR) and spatial resolution were measured by combining the fabricated Gd2O3:Eu screen films with a lens-coupled CCD imaging detector under radiographic system conditions.

Design and image-quality performance of high resolution CMOS-based X-ray imaging detectors for digital mammography

In digital X-ray imaging systems, X-ray imaging detectors based on scintillating screens with electronic devices such as charge-coupled devices (CCDs), thin-film transistors (TFT), complementary metal oxide semiconductor (CMOS) flat panel imagers have been introduced for general radiography, dental, mammography and non-destructive testing (NDT) applications. Recently, a large-area CMOS active-pixel sensor (APS) in combination with scintillation films has been widely used in a variety of digital X-ray imaging applications. We employed a scintillator-based CMOS APS image sensor for high-resolution mammography. In this work, both powder-type Gd2O2S:Tb and a columnar structured CsI:Tl scintillation screens with various thicknesses were fabricated and used as materials to convert X-ray into visible light. These scintillating screens were directly coupled to a CMOS flat panel imager with a 25 × 50 mm2 active area and a 48 μm pixel pitch for high spatial resolution acquisition. We used a W/Al mammographic X-ray source with a 30 kVp energy condition. The imaging characterization of the X-ray detector was measured and analyzed in terms of linearity in incident X-ray dose, modulation transfer function (MTF), noise-power spectrum (NPS) and detective quantum efficiency (DQE).

Scintillation efficiency and X-ray imaging with the RE-Doped LuAG thin films grown by liquid phase epitaxy

Very thin scintillator imaging plates have recently become of great interest. In high resolution X-ray radiography, very thin scintillator layers of about 5–20 μm are used to achieve 2D-spatial resolutions below 1 μm. Thin screens can be prepared by mechanical polishing from single crystals or by epitaxial growth on single-crystal substrates using the Liquid Phase Epitaxy technique (LPE). Other types of screens (e.g. deposited powder) do no reach required spatial resolutions. This work compares LPE-grown YAG and LuAG scintillator films doped with different rare earth ions (Cerium, Terbium and Europium). Two different fluxes were used in the LPE growth procedure. These LPE films are compared to YAG:Ce and LuAG:Ce screens made from bulk single crystals. Relative light yield was detected by a highly sensitive CCD camera. Scintillator screens were excited by a micro-focus X-ray source and the generated light was gathered by the CCD camera’s optical system. Scintillator 2D-homogeneity is examined in an X-ray imaging setup also using the CCD camera. ► Novel thin film scintillation detectors for high resolution 2D X-ray imaging. ► Comparison of LPE-made and mechanically prepared detectors. ► Practical setup for 2D X-ray micro imaging and its resolution capability.

CMOS 기반 X선 영상의 해상력 향상을 위한 Gd2O2S:Tb 미세형광체 필름 제작 및 영상 질 평가

본 연구는 고해상도 디지털 X선 영상 검출기 적용을 위해 미세 <TEX>$Gd_2O_2S$</TEX>:Tb 형광체 분말을 저온 액상법을 이용하여 합성하였다. 제조된 형광체 분말을 이용하여 입자침전법을 이용하여 형광체 필름을 제작하여 발광특성을 조사하였다. 측정결과, Tb 첨가농도에 따른 상대적인 발광량 측정결과 5 wt%의 첨가농도에서 가장 높은 발광효율을 보였으며, 첨가농도가 증가할수록 소광현상에 의한 발광강도가 급격히 감소하는 경향을 보였다. 또한 270 <TEX>${\mu}m$</TEX> 두께의 <TEX>$Gd_2O_2S$</TEX>:Tb에서 2945 pC/<TEX>$cm^2$</TEX>/mR의 발광 강도를 가졌으며, 발광 강도가 거의 포화되는 것을 관찰할 수 있었다. 끝으로 제조된 형광체의 영상획득 성능을 평가하기 위해 상용화된 CMOS 센서를 이용하여 X선 영상을 획득하여 MTF, NPS를 측정하여 DQE 평가를 수행하였다. 측정결과, DQE(0)의 값은 37%로 다소 낮은 값을 보였다. 향후 필름 제조 공정상의 문제점을 해결한다면, DQE를 개선할 수 있을 것으며, 고해상도 의료 방사선 영상 시스템 적용에 유용하게 적용 가능할 것으로 판단된다. In this study, fine <TEX>$Gd_2O_2S$</TEX>:Tb powder was synthesized by using a low temperature solution-combustion method for a high-resolution digital x-ray imaging detector. From the fabricated phosphor power, the fine scintillator films was fabricated by particle sedimentation method and was investigated the luminescent property. From the experimental results of relative light output as a function of terbium concentration, the highest luminescent efficiency has at 5 wt% Tb concentration, and luminescent intensity decreased rapidly according to quenching effect about higher Tb concentration. Also, the relative light output of <TEX>$270{\mu}m$</TEX>-<TEX>$Gd_2O_2S$</TEX>:Tb film has 2945 pC/<TEX>$cm^2$</TEX>/mR. And light intensity was saturated at higher film thickness. Finally, to evaluate an image acquisition performance of fabricated phosphor, images were obtained by using commercial CMOS sensor and measured the MTF, NPS, and DQE. DQE(0 lp/mm) of fine phosphor film has 37%. But, DQE improvement of fine phosphor film is possible by resolving problem of film fabrication process and has a significant potential in the application of digital radiation imaging system later.

High-Resolution Chemical Imaging through Tissue with an X-ray Scintillator Sensor

We describe a novel method for high-resolution chemical imaging on a surface embedded in tissue. The sensor surface consists of an X-ray scintillator film coated in a thin film loaded with chemical indicator dye. A narrow scanning X-ray beam is used to excite luminescence from X-ray scintillators located within the beam. This luminescence passes through the indicator film, and the spectrum is analyzed to measure chemical concentrations at that location. A pH sensor is demonstrated with a dynamic range between pH 6-9 and noise level of 0.05 pH units using methyl-red dyed pH paper. The location of the interface between two types of scintillator films is obtained with 0.30 mm spatial resolution even though the images are highly blurred by 10 mm of chicken breast. This work has important applications for detecting pH changes on surfaces of implanted medical devices.