Structured Scintillators for Efficient Radiation Detection

Abstract

Scintillators, which can convert high-energy ionizing radiation into visible light, have been serving as the core component in radiation detectors for more than a century of history. To address the increasing application demands along with the concern on nuclear security, various strategies have been proposed to develop a next-generation scintillator with a high performance in past decades, among which the novel approach via structure control has received great interest recently due to its high feasibility and efficiency. Herein, the concept of "structure engineering" is proposed for the exploration of this type of scintillators. Via internal or external structure design with size ranging from micro size to macro size, this promising strategy cannot only improve scintillator performance, typically radiation stopping power and light yield, but also extend its functionality for specific applications such as radiation imaging and therapy, opening up a new range of material candidates. The research and development of various types of structured scintillators are reviewed. The current state-of-the-art progresses on structure design, fabrication techniques, and the corresponding applications are discussed. Furthermore, an outlook focusing on the current challenges and future development is proposed.

Keywords: arrays; fibers; particles; radiation detection; structured scintillators.

Figure 1

Structure engineering toward next‐generation scintillators.

Figure 2

Schematic diagram of particle–polymer structured scintillators incorporated with a) emitting particles and b) nonemitting particles. c,d) Photograph and pulse height spectrum of structured scintillator incorporated with emitting LaF₃:Ce particles. e,f) TEM image and pulse height spectrum of structured scintillator incorporated with nonemitting Gd₂O₃ particles and dye. Inset: photograph. c,d) Reproduced with permission.^{[ 28 ]} Copyright 2007, Elsevier. e,f) Reproduced with permission.^{[ 19 ]} Copyright 2013, Royal Society of Chemistry.

Figure 3

a–c) X‐ray image sensor based on structured scintillator embedded with GOS particles. a) Schematic of image sensor with an a‐Si:H backplane and a hybrid frontplane. b) 70 kV X‐ray image (magnified to region of interest) of a resolution test target. c) MTF of images with different layer thicknesses and two conventional indirect X‐ray converters. Theoretical limit is determined by pixel size. d–f) Flexible X‐ray detector based on structured scintillator embedded with lanthanide‐doped nanoparticles. d) Schematic showing imaging of curved 3D objects. e) Imaging of a 3D electronic board using a prototype detector and f) conventional flat‐panel X‐ray detector. a–c) Reproduced with permission.^{[ 29 ]} Copyright 2015, Springer Nature. d–f) Reproduced with permission.^{[ 30 ]} Copyright 2021, Springer Nature.

Figure 4

a) Photograph of structured scintillator incorporated with nonemitting BaF₂ nanoparticles and b) dependence of luminescence intensities on X‐ray excitation of different particle sizes. c–f) Bulk transparent structured scintillators embedded with Cd _x Zn_{1‐ x} S/ZnS quantum dots. c) Photograph. d)TEM image. e) Chart of scintillation light yields. f) Pulse height spectrum. g–i) Structured scintillator incorporated with CsPbBr₃ quantum dots. g) Energy level of embedded CsPbBr₃ quantum dots and dye. h) Photoluminescence spectra. Inset: photographs illuminated by ambient light (left) and 400 nm light (right). i) Radioluminescence spectra under X‐ray irradiation (30 kV, 20 mA). j) Photograph of structured scintillator embedded with isotopically ⁶Li₂ ¹⁰B₄O₇ nanoparticles and k) subtracted spectra of pulse shape discrimination. a,b) Reproduced with permission.^{[ 14 ]} Copyright 2016, Elsevier. c–f) Reproduced with permission.^{[ 34 ]} Copyright 2017, American Chemical Society. g–i) Reproduced with permission.^{[ 35 ]} Copyright 2020, Springer Nature. j,k) Reproduced with permission.^{[ 39 ]} Copyright 2019, Royal Society of Chemistry.

Figure 5

a–c) Fully crystallized BaAl₄O₇:Eu^{2 +} structured scintillator. a) Photoluminescence and radioluminescence spectra. b) Decays under pulse laser excitation at 380 nm and under excitation (662 keV from a ¹³⁷Cs source). c) Pulse height spectra under ¹³⁷Cs irradiation. d–f) Structured scintillators embedded with CaF₂:Sm³⁺/Sm²⁺ nanocrystals.d) Dose–response curve. e) Dose distribution image of microbeam recorded and digitized using confocal photoluminescence microscopy. f) Photoluminescence spectra recorded during two erasure processes: (top) heat erasure and (bottom) optical erasure. a–c) Reproduced with permission.^{[ 46 ]} Copyright 2014, Royal Society of Chemistry. d–f) Reproduced with permission.^{[ 56 ]} Copyright 2014, Wiley‐VCH.

Figure 6

a–c) Particle–glass structured scintillator loaded with CdSe/ZnS quantum dots. a) Photograph. Pulse height spectrum excited by b) alpha particles and c) gamma‐ray. d–i) Structured scintillators precipitated with CsPb(Cl,Br)₃ perovskite quantum dots. d) Photographs of multicolor radioluminescence under X‐ray irradiation. e) XRD patterns (left) and photographs (right). f) Bright‐field TEM image. g) X‐ray excited luminescence spectrum. h) Temperature‐dependent integrated emission intensity during heating–cooling cycles. i) Photographs and luminescent photos of the structured scintillators after X‐ray irradiation with different powers and then reheating at 350 °C for 2 h. a–c) Reproduced with permission.^{[ 59 ]} Copyright 2006, American Chemical Society. d–i) Reproduced with permission.^{[ 60 ]} Copyright 2020, Elsevier.

Figure 7

a) SEM images of surface morphology of CsI:Tl thin film and b) photoluminescent spectra with different deposition rate.c‐j) Self‐growth Lu₂O₃:Eu array‐derived structured scintillator for high‐resolution radioluminescence microscopy. c) SEM image showing the 6 µm Lu₂O₃:Eu film deposited on a sapphire substrate. d) 20 keV X‐ray excited luminescence spectrum. Bright field, radioluminescence, and overlaid micrographs of MDA‐MB‐231 cells imaged using e‐g) Lu₂O₃:Eu and h‐j) CdWO₄. a–b) Reproduced with permission.^{[ 64 ]} Copyright 2017, Elsevier. c‐j) Reproduced with permission.^{[ 74 ]} Copyright 2015, Wiley‐VCH.

Figure 8

Influence of Eu dopant concentration on a) optical transmittance spectra and b) pulse height spectrum of CaF₂/LiF structured scintillator. c) SEM images and d) pulse height spectrum of SrF₂/LiF structured scintillator. e–h) Array‐derived structured scintillators with rod‐like feature. e) Luminescence image under 312 nm UV light. f, g) SEM images of the representative CsI/NaCl sample. h) Line profiles of spot‐excited images for representative CsI/NaCl:Tl (solid line) and CsBr/NaF:In (dotted line) sample. Inset: image of spot‐excited CsI/NaCl:Tl sample. a,b) Reproduced with permission.^{[ 80 ]} Copyright 2015, Springer Nature. c,d) Reproduced with permission.^{[ 81 ]} Copyright 2013, Elsevier. e–h) Reproduced with permission.^{[ 86 ]} Copyright 2012, Wiley‐VCH.

Figure 9

a–f) GdAlO₃/Al₂O₃ array‐derived structured scintillators with rod‐like feature. a) Schematic diagram. b) Photograph. c,d) SEM images. e) Optical transmission microscope images illuminated by a parallel incident white light source of the 1100 µm thick sample (top) and enlarged area with different incident light angles (down). f) Images of gold grating phantoms with aperture‐pitch sizes of 22–43, 9–22, and 4–8.2 µm. g–l) Ultrahigh‐resolution radiation imaging system based on GdAlO₃/Al₂O₃ structured scintillators. g) Photograph. h) SEM images. i) Structure of the radiation imaging system. j–l) Images of typical alpha particles, beta particles, and gamma photons. a–f) Reproduced with permission.^{[ 88 ]} Copyright 2013, ‐AIP Publishing. g–l) Reproduced with permission.^{[ 89 ]} Copyright 2018, Springer Nature.

Figure 10

Schematic diagram and SEM image of a,b) template with surface pattern and c,d) template with pore array. e–g) CsI(Tl) structured scintillator synthesized with a surface patterned template. e,f) SEM images of the structured scintillator with 10 µm column interval. g) Measured MTF curves of the scintillators of various column intervals. b,e–g) Reproduced with permission.^{[ 91 ]} Copyright 2007, Elsevier. d) Reproduced with permission.^{[ 93 ]} Copyright 2008, Wiley‐VCH.

Figure 11

a–f) Influence of pore shape and pore array arrangement on performance of CsI structured scintillator studied via simulation. a) Schematic diagram of different pore shapes and their effect on b) X‐ray absorptions and c) proportion of photons left after total reflection. d) Schematic diagram of different pore array arrangements and their effect on e) X‐ray absorptions and f) MTFs. g–i) Compact CsI structured scintillator with hexagonal array arrangement. g) SEM image. h) X‐ray image. i) MTF curves of fabricated CsI structured scintillator. Inset: X‐ray image of a lead slit. a–f) Reproduced with permission.^{[ 97 ]} Copyright 2018, Springer Nature. g–i) Reproduced with permission.^{[ 98 ]} Copyright 2018, Elsevier.

Figure 12

a–c) Structured scintillator with a pillar array structured coating fabricated by nano imprint lithography. a) Photo of the nano imprinted surface showing the typical iridescent diffraction effects. b) SEM image of sample tilted by 70 degrees with 20k magnification. c) . Ratio of the coincidence time resolution obtained for the patterned crystal and the reference crystal. d‐f) LYSO structured scintillator with external coating. d) Simulated transmission at 415 nm as a function of incident angle. e) Photoluminescence spectra in the normal direction. Inset: enhancement ratio with respect to the reference sample. f) Experimental and simulated enhancement ratio of light extraction at 415 nm emission.a–c) Reproduced with permission.^{[ 107 ]} Copyright 2019, Elsevier. d‐f) Reproduced with permission.^{[ 108 ]} Copyright 2013, AIP Publishing.

Figure 13

a–c) Neutron imaging with Tb³⁺/Ce³⁺ codoped Gd₂O₃ glass fiber‐derived structured scintillator. a) Photograph. b) Photoluminescence spectra of 0.3 mm thick core glass and three structured scintillators with differing thicknesses. c) Cold neutron image of the PSI Siemens Star with the 0.3 mm thick structured scintillators cold neutron imaging system. d–f) Glass fiber‐derived structured scintillator embedded with GdTaO₄ nanocrystals. d) HRTEM image. Inset: photograph of the parent bulk glass sample. e) Photograph of glass fiber‐derived structured scintillator. f) Optical microscope image of fiber array under natural light (left) and ultraviolet light (right). g–j) Glass fiber‐derived structured scintillator embedded with Bi₂GeO₅ nanocrystals. g) Transmittance spectra (left) and TEM images (right). h) Optical microscopy image under natural light and 365 nm UV light. i) Fiber cross‐section with and without 365 nm light excitation. j) Luminescence intensity distribution at the end of fiber. a‐c) Reproduced with permission.^{[ 121 ]} Copyright 2020, Elsevier. d–f) Reproduced with permission.^{[ 123 ]} Copyright 2017, American Chemical Society. g–j) Reproduced with permission.^{[ 43 ]} Copyright 2020, American Chemical Society.

Figure 14

Photographs of representative crystal fiber‐derived structured scintillators. a) BGO. b) LuAG and c) the related calorimeter prototype. d) YAG. e) YAP. a) Reproduced with permission.^{[ 127 ]} Copyright 2019, Elsevier. b) Reproduced with permission.^{[ 129 ]} Copyright 2016, Elsevier. c) Reproduced with permission.^{[ 130 ]} Copyright 2016, IOP Publishing. d) Reproduced with permission.^{[ 133 ]} Copyright 2019, Royal Society of Chemistry. e) Reproduced with permission.^{[ 134 ]} Copyright 2007, Elsevier.

Figure 15

Constructed devices based on polymer fiber‐derived structured scintillators. a) Protype fiber dosimeter basing on BCF‐10 fiber‐derived structured scintillators for real‐time gamma‐ray and neutron monitoring on radiotherapy accelerators. b) The sensor device based on BCF‐20 structured scintillators toward alpha particle detection in liquids for application of radioisotope monitoring. c) Multipoint in vivo dosimeter based on BCF‐10, BCF‐12, and BCF‐60 fiber‐derived structured scintillators for application of high dose rate brachytherapy. a) Reproduced with permission.^{[ 137 ]} Copyright 2007, Elsevier. b) Reproduced with permission.^{[ 139 ]} Copyright 2019, Elsevier. c) Reproduced with permission.^{[ 140 ]} Copyright 2019, Wiley‐VCH.