Radioluminescence Research Articles

Heterovalent Co‐Doped LiLuF4 Composite Flexible Films as Persistent Luminescence Scintillator for X‐Ray High‐Resolution Extension Imaging

AbstractScintillators with high light yield, spatial resolution, and detection sensitivity are desirable for X‐ray imaging. Howerer, it remains challenging to improve the light yield and radiation detection capability of alkali metal rare‐earth fluoride (ALnF4). Herein, a type of Cu2+ ion heterovalent co‐doped LiLuF4:Tb,Cu microcrystalline scintillation material with high light yield, persistent, and thermostimulated luminescence is obtained by defect engineering. The heterovalent codoping strategy not only increases the radioluminescence (RL) intensity, but also introduces more carrier traps in the material to enhance the long‐afterglow and thermoluminescence intensity of LiLuF4:Tb microcrystals. After doping of 3 mol% Cu2+ ions, the RL efficiency is increased by 88.61%, and the X‐ray detection limit of LiLuF4:Tb,Cu reaches 2.7928 nGy·s‒1. This detectivity is considerably lower than the medical imaging requirements (5.5 µGy·s‒1). Furthermore, a large‐area flexible scintillation film of dimensions 30 × 30 cm2 is prepared to achieve high spatial resolution X‐ray imaging of 22 LP mm−1@MTF(modulation transfer function) = 0.2. Besides, this flexible film enables X‐ray imaging of curved objects and stores optical information for >48 h. This work provides a paradigm for improving the RL intensity and X‐ray detection sensitivity of alkali rare‐earth fluorides by crystal defect engineering, and enriches X‐ray high resolution extended imaging applications.

Mechanochemical Synthesis of Cuprous Complexes for X-ray Scintillation and Imaging.

Cuprous complex scintillators show promise for X-ray detection with abundant raw materials, diverse luminescent mechanisms, and adjustable structures. However, their synthesis typically requires a significant amount of organic solvents, which conflict with green chemistry principles. Herein, we present the synthesis of two high-performance cuprous complex scintillators using a simple mechanochemical method for the first time, namely [CuI(PPh3)2R] (R = 4-phenylpyridine hydroiodide (PH, Cu-1) and 4-(4-bromophenyl)pyridine hydroiodide (PH-Br, Cu-2). Both materials demonstrated remarkable scintillation performances, exhibiting radioluminescence (RL) intensities 1.52 times (Cu-1) and 2.52 times (Cu-2) greater than those of Bi4Ge3O12 (BGO), respectively. Compared to Cu-1, the enhanced RL performance of Cu-2 can be ascribed to its elevated quantum yield of 51.54%, significantly surpassing that of Cu-1 at 37.75%. This excellent luminescent performance is derived from the introduction of PH-Br, providing a more diverse array of intermolecular interactions that effectively constrain molecular vibration and rotation, further suppressing the nonradiative transition process. Furthermore, Cu-2 powder can be prepared into scintillator film with excellent X-ray imaging capabilities. This work establishes a pathway for the rapid, eco-friendly, and cost-effective synthesis of high-performance cuprous complex scintillators.

Self-absorption and investigation of excited carrier dynamics in two-dimensional perovskite scintillator

The PEA2PbBr4 scintillator exhibits varied performance in photoluminescence (PL) and radioluminescence (RL) profiles. PL in the reflectivity mode shows emission peaks at 414 and 434 nm, whereas PL and RL in the transmission mode exhibit only one peak at 434 nm. Temperature-dependent PL spectra measurements confirm that self-absorption contributes to this difference. PEA2PbBr4 displays decay times of 1.3 ns (90%) and 4.4 ns (10%) for PL and 11.5 ns (89%) and 47 ns (11%) for RL. To explain the distinct decay times, we construct two models for simulating laser and radiation excitation and investigate carrier dynamics using non-adiabatic molecular dynamics. Our findings suggest that the relatively long radiative recombination process of carriers contributes to the slow RL decay time.

Development and characterisation of a plastic scintillator dosemeter in high-energy photon beams.

The radioluminescent (RL) dosemeter is excellent for real-time radiation measurement and can be used in various applications. A plastic scintillator is often the choice sensor because of its size and tissue equivalency. This study aims to characterise a novel plastic scintillator irradiated with high-energy photon beams. An RL dosimetry system was developed using the plastic scintillator. The RL dosimetry system was irradiated using a linear accelerator to characterise the dose linearity, dose rate, energy dependency and depth dose. The developed system showed a linear response toward the dose and dose rate. An energy dependency factor of 1.06 was observed. Depth dose measurement showed a mean deviation of 1.21% from the treatment planning system. The response and characteristics of the plastic scintillator show that it may be used as an alternative in an RL dosimetry system.

Photoluminescence and X-ray induced scintillation in Gd3+-Tb3+ co-doped fluoride-phosphate glasses, and derived glass-ceramics containing NaGdF4 nanocrystals

The glass system (50NaPO3–20BaF2–10CaF2–20GdF3)-xTbCl3 with x = 0.3, 1, 3, 5, and 10 wt % was investigated. We successfully produced transparent glass ceramic (GC) scintillators with x = 1 through a melt-quenching process followed by thermal treatment. The luminescence and crystallization characteristics of these materials were thoroughly examined using various analytical methods. The nanocrystallization of Tb3+-doped Na5Gd9F32 within the doped fluoride-phosphate glasses resulted in enhanced photoluminescence (PL) and radioluminescence (RL) of the Tb3+ ions. The GC exhibited an internal PL quantum yield of 33 % and the integrated RL intensity across the UV-visible range was 36 % of that reported for the commercial BGO powder scintillator. This research showcases that Tb-doped fluoride-phosphate GCs containing nanocrystalline Na5Gd9F32 have the potential to serve as efficient scintillators while having lower melting temperature compared to traditional silicate and germanate glasses.

Radioluminescence properties of Sm3+-doped Y3Al5O12 single crystals

0.1, 0.3, 0.5, 1.0, 5.0, and 10.0 % Sm3+-doped Y3Al5O12 single crystals were grown by the floating zone method. Photoluminescence (PL) and radioluminescence (RL) properties of the samples were evaluated and the emission peaks due to 4f-4f transitions of Sm3+ ions were observed. The PL quantum yield of the 0.3 % Sm3+-doped sample was highest among all the samples (approximately 48 %). PL and RL decay times of the samples were 0.7–2.7 and 0.6–2.9 ms, respectively. The light yield of the 0.5 % Sm3+-doped sample under γ-ray excitation was highest and its value was estimated to be approximately 8400 photons/MeV using a measurement system for scintillators with slow decay times.

Luminescence characteristics and kinetic parameters of LiBaPO4: Tb3+, Dy3+ phosphors synthesized by sol-gel method

LiBaPO4: Tb3+, Dy3+ phosphors were prepared via sol-gel method by using the stoichiometric amounts of lithium nitrate LiNO3, barium nitrate Ba(NO3)2 and ammonium dihydrogen phosphate NH4H2PO4 as base materials. Morphology by scanning electron microscopy (SEM), structure by X-ray diffraction (XRD), thermal properties by Differential thermal analysis (DTA)/Thermogravimetric Analysis (TGA) and structural characteristics by Fourier transform infrared spectroscopy (FT-IR) were investigated. This paper presents luminescence properties using spectra from radioluminescence (RL), photoluminescence (PL), cathodoluminescence (CL) and, thermoluminescence (TL) and the influence of RE dopants (Tb3+, Dy3+) on the luminescent behavior of LiBaPO4. Computerized Glow Curve Deconvolution (CGCD) and Peak Shape Method were used to determine the kinetic parameters and the obtained results were evaluated. The RL results of un-doped LiBaPO4 showed the presence of a well-defined peak at 417 nm and a weaker band around 685 nm. Strong emissions were detected in the sample doped with Dy3+ correspond to 4F9/2→6Hj transitions. Blue, yellow and red emissions were observed with transitions of 4F9/2 → 6H15/2, 4F9/2 → 6H13/2 and 4F9/2 → 6H11/2, respectively. As for LiBaPO4: Tb3+, green emissions originated from the characteristic transitions (5D3 → 7FJ (j = 6–3) and 5D4 → 7FJ (j = 6–1)) of Tb+3 ion was seen. The RL, PL and CL spectra were identical, suggesting these green emissions. Dy3+ doped sample has three glow curves located at 72 °C, 145 °C and 204 °C, while the main temperature peak is measured at 240 °C for Tb3+ doped sample. Chromotographic studies of LiBa0·98PO4: Dy3+0.02 reveals that calculated x and y color coordinates (0.3122, 0.3233) are very close to the white light.

Highly stable multi-responsive yellow-emissive fluoride RbCdF3:Mn2+,Yb3+ for advanced optical anti-counterfeiting

Multi-responsive luminescent materials have significant advantages in optical anti-counterfeiting owing to the diversity of their luminescence modes. However, the development of multi-responsive luminescent materials that simultaneously exhibit more than three types of luminescence modes remains challenging. Herein, RbCdF3:Mn2+,Yb3+, a novel multi-responsive fluoride that exhibits all luminescence modes of Stokes, upconversion (UC), radioluminescence (RL), persistent luminescence (PersL), photostimulated luminescence (PSL), and thermoluminescence luminescence (TL) is developed. All modes produce bright-yellow emission (∼565 nm). Moreover, the PersL of RbCdF3:Mn2+,Yb3+ can be charged by both the high-energy X-rays and commercial 254 nm UV lamp, which is rarely observed for fluorides. Furthermore, RbCdF3:Mn2+,Yb3+ also exhibits superior luminescence stability at high temperatures and high humidity. Specifically, the emission intensity at 498 K is 141.14 % of that at room temperature, and retains 76.47 % after being dispersed in water for 50 days when excited by 254 nm light. The unique multi-responsive luminescent features and excellent environmental stability endow RbCdF3:Mn2+,Yb3+ with great potential for practical applications in advanced optical anti-counterfeiting.

Halogen-bonding boosting the high performance X-ray imaging of organic scintillators.

Organic scintillators with efficient X-ray excited luminescence are essential for medical diagnostics and security screening. However, achieving excellent organic scintillation materials is challenging due to low X-ray absorption coefficients and inferior radioluminescence (RL) intensity. Herein, supramolecular interactions are incorporated, particularly halogen bonding, into organic scintillators to enhance their radioluminescence properties. By introducing heavy atoms (X=Cl, Br, I) into 9,10-bis(4-pyridyl)anthracene (BPA), the formation of halogen bonding (BPA-X) enhances their X-ray absorption coefficient and restricts the molecular vibration and rotation, which boosts their RL intensity. The RL intensity of BPA-Cl and BPA-Br fluorochromes increased by over 2 and 6.3 times compared to BPA, respectively. Especially, BPA-Br exhibits an ultrafast decay time of 8.25ns and low detection limits of 25.95±2.49nGys-1. The flexible film constructed with BPA-Br exhibited excellent X-ray imaging capabilities. Furthermore, this approach is also applicable to organic phosphors. The formation of halogen bonding in bromophenyl-methylpyridinium iodide (PYI) led to a fourfold increase in RL intensity compared to bromophenyl-methyl-pyridinium (PY). It suggests that halogen bonding serves as a promising and effective molecular design strategy for the development of high-performance organic scintillator materials, presenting new opportunities for their applications in radiology and security screening.

Luminescence intensity-tunable X-ray scintillation based on zirconium-based metal-organic frameworks

The low-energy ultraviolet or visible photons can be produced by the interaction between the scintillator materials and ionizing radiation. For this reason, scintillator materials are widely used as radiation detectors, which are prevalently utilized in different applications such as nuclear medicine imaging, homeland security, high-energy physics, oil drilling explorations, etc. Herein, a high-atomic-number (Z) zirconium-based metal-organic framework nanoflower material CJLU-1 (Zr6(μ3-O)4(μ3-OH)4(OH)6(TCA)2(H2O)6) (H3TCA = tri-carboxylic acids 4,4′,4″-nitrilotribenzoic acid) was synthesized and can effectively convert X-ray into visible light. CJLU-1 is composed of secondary structural unit hexagonal Zr metal cluster and connected by TCA ligands. The photo luminescence spectra (PL) emission peak and excitation peak of CJLU-1 are at 470 nm and 395 nm respectively. CJLU-1 exhibited radioluminescence (RL) peak with a maximum at 480 nm under steady-state excitation with X-rays. Moreover, by accommodating different guest molecules such as xylene and RhB in the same MOF material, intensity-tunable X-ray scintillation can be facilely achieved, providing a new class of scintillating materials with luminescence intensity tunability. The high-Z hexagonal Zr clusters, which are arranged in an orderly fashion, absorb and interact with the ionizing radiation and sensitize the adjacent organic ligands TCA to produce efficient RL. This work contributes to the development of high-Z zirconium-based MOFs and RL intensity-tunable scintillation materials towards future practical nuclear sensing applications.

Gd3+-sensitized rare earth fluoride scintillators for High-resolution flexible X-ray imaging

X-ray imaging technology is widely used in the medical, industrial, and scientific fields, where highly sensitive, flexible, and cost-effective scintillation screens are crucial prerequisites. In this work, YF3:Gd3+/Tb3+ microparticles (MPs) were prepared via an ultrafast chemical precipitation method and exhibited excellent luminescent properties under the excitation of ultraviolet light and X-ray. It was found that Gd3+ doping could effectively enhance the photoluminescence (PL) and X-ray activated radioluminescence (RL) of Tb3+ owing to an efficient energy transfer process from Gd3+ to Tb3+. The prepared YF3:30%Gd3+/10%Tb3+ MPs exhibited fine environmental stability and superb X-ray RL, which was stronger than that of commercial scintillators Bi4Ge3O12 (BGO) and even comparable to that of CsI:TI single crystal. Highly flexible transparent YF3:Gd3+/Tb3+/PDMS scintillation screens were prepared to record high-resolution X-ray images of planar/nonplanar objects, where the imaging spatial resolution was 16.8 lp mm−1, which was far higher than the standard spatial resolutions required for medical computed tomography (CT) scan (2 lp mm−1) and X-ray imaging (3.5 lp mm−1). The excellent scintillation performance, superior flexibility and environmental stability of YF3:Gd3+/Tb3+/PDMS scintillation films endow them with the potential application in high-resolution industrial nondestructive inspection and biological imaging.

Application of LiMgPO4 crystal for proton beam quality control in radiotherapy.

The radioluminescence (RL) emitted by LiMgPO4 detector under proton beam irradiation was investigated in real time at the radiotherapy facility in the Institute of Nuclear Physics Polish Academy of Sciences in Krakow. The facility uses protons accelerated by the AIC-144 isochronous cyclotron up to the energy of 60MeV. The measurements of RL were carried out using a remote optical fiber device with a luminophore detector and photomultiplier located at opposite ends of the optical fiber. A thin slice of LiMgPO4 doped with Tm (1.2mol%) crystal was exposed to the proton beam. The tested detector allowed for the measurement of proton beam current, flux fluence and determination of proton beam time structure parameters. The investigation of LiMgPO4 crystal showed its high sensitivity, fast reaction time to irradiation and possibility of application as the detector for control of proton beam parameters.

Li9Mg3[PO4]4F3 fluorophosphate as a new thermoluminescent material: Experimental and theoretical study

In this work, radioluminescence (RL), thermoluminescence (TL) and photoluminescence (PL) of fluorophosphate Li9Mg3[PO4]4F3 as a possible dosimetry material are studied for the first time. It was found that the irradiated sample exhibits significant thermoluminescence in the temperature range of 100–300°С with the main peak at 205°С. The RL, PL and TL spectra consist of one broad band centered at 400 nm which was attributed to defects in the structure of Li9Mg3[PO4]4F3. The energy required to excite defects in Li9Mg3[PO4]4F3 determined by UV–vis spectroscopy is 4.4 eV (λ ≈ 280 nm). Additional evidence for intrinsic defects was obtained from the electron paramagnetic resonance (EPR) in Li9Mg3[PO4]4F3. The DFT method was employed to simulate various defects including single and complex, neutral and charged vacancies. The formation energies of vacancies were predicted and their effect on the electronic structure and optical properties was established. These intrinsic defects introduce additional electronic states into the band gap and absorption bands in the visible region, the position and intensity of which strongly depend on the type of defect. Our experimental and theoretical studies reveal that Li9Mg3[PO4]4F3 can be a promising optical matrix suitable for dosimetric applications. As evidence, the main functional characteristics of the new material are given.

Density-discriminating chromatic x-ray imaging based on metal halide nanocrystal scintillators.

X-ray imaging based on a single gray level shows visual blind parts and affects accurate judgment in some situations. Color-cognized x-ray imaging will boost the recognition capability, which has not yet been reported. Here, we propose a quartz-assisted chromatic x-ray imaging model based on metal halide nanocrystal (NC) stacked scintillators. Mutually inactive (BA)2PbBr4:Mn and Cs3Cu2I5:Tl enable x-ray energy- or density-dependent radioluminescence (RL) color variation. The upper scintillator light yield and the bottom scintillator transmittance are enhanced by elaborate in situ passivation of phenethylamine bromide and NC orientation regulation, respectively. Imaging targets with different densities are distinguished on RL spectra, and the color coordinates shift linearly on CIE 1931. An algorithm balances the image details of different gray areas and enhances the visual perception by color filling. This work provides color recognition between objects with different densities and takes a step toward chromatic x-ray imaging applied to practical scenarios.

Surfactant-Dependent Bulk Scale Mechanochemical Synthesis of CsPbBr3 Nanocrystals for Plastic Scintillator-Based X-ray Imaging.

We report a facile, solvent-free surfactant-dependent mechanochemical synthesis of highly luminescent CsPbBr3 nanocrystals (NCs) and study their scintillation properties. A small amount of surfactant oleylamine (OAM) plays an important role in the two-step ball milling method to control the size and emission properties of the NCs. The solid-state synthesized perovskite NCs exhibit a high photoluminescence quantum yield (PLQY) of up to 88% with excellent stability. CsPbBr3 NCs capped with different amounts of surfactant were dispersed in toluene and mixed with polymethyl methacrylate (PMMA) polymer and cast into scintillator discs. With increasing concentration of OAM during synthesis, the PL yield of CsPbBr3/PMMA nanocomposite was increased, which is attributed to reduced NC aggregation and PL quenching. We also varied the perovskite loading concentration in the nanocomposite and studied the resulting emission properties. The most intense PL emission was observed from the 2% perovskite-loaded disc, while the 10% loaded disc exhibited the highest radioluminescence (RL) emission from 50 kV X-rays. The strong RL yield may be attributed to the deep penetration of X-rays into the composite, combined with the large interaction cross-section of the X-rays with the high-Z atoms within the NCs. The nanocomposite disc shows an intense RL emission peak centered at 536 nm and a fast RL decay time of 29.4 ns. Further, we have demonstrated the X-ray imaging performance of a 10% CsPbBr3 NC-loaded nanocomposite disc.

High-Quality Cs3Cu2I5@PMMA Scintillator Films Assisted by Multiprocessing for X-ray Imaging.

In recent years, novel metal halide scintillators have shown great application potential due to their tunable emission wavelength, high X-ray absorption, and high luminescence efficiency. However, poor stability and complex device packaging remain key issues for metal halide scintillators, making it difficult to achieve high-resolution and flexible X-ray imaging applications. To address the above issues, a multiprocessing strategy was introduced to prepare Cs3Cu2I5@PMMA scintillator films for long-term stable application, mainly undergo different annealing treatments to make Cs3Cu2I5 crystals to accurately nucleate and then grow in-situ in the PMMA matrix. Then, a series of characterization results illustrate that the prepared Cs3Cu2I5@PMMA scintillator films have high crystallinity, uniform size, excellent flexibility, high stable photoluminescence (PL) and radioluminescence (RL) performance, and high-resolution X-ray imaging capability. Most importantly, Cs3Cu2I5@PMMA scintillator films can not only provide clear and accurate imaging recognition of objects with different complex structures but also maintain stable X-ray imaging quality within 60 days and can achieve flexible X-ray imaging. Therefore, we have provided an effective strategy for producing high-quality scintillator films to meet the multidimensional needs of a new generation of scintillators.

Radiation Induced Attenuation and Luminescence Study in Radioluminescent Optical Fibers

We present experimental characterization of both RIA (Radiation Induced Attenuation) and RL (Radioluminescence) of differently doped optical fibre radiation sensors. We present data for different sample lengths and Total Ionizing Dose (TID) up to 600 kGy (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) under X-rays. Combined RIA and RL responses are used to attempt explaining the variation of the RL signal with TID on those fibres.

Radioluminescence Processes in Cerium-Doped Silica Glasses

Rare-earth-doped silica glasses are promising materials for ionizing radiation dosimetry. In this paper, a bulk glassy silica doped with Ce ions, was prepared via the sol-gel technique and drawn at about 2000 °C into a cylindrical capillary rod. Under X-rays, this sample presents a radioluminescence (RL) signal that can be exploited for dose rate real-time monitoring with remarkable linear response spanning 6 decimal orders of magnitude. In order to elucidate RL signal dynamics associated with free carriers trapping-detrapping and recombination during and after X-ray irradiation, we studied the obtained RL signals using a kinetic model involving one or several trapping states and one recombination center. With this model and using appropriate sets of trapping parameters, extracted from the thermoluminescence data, the RL signal was numerically simulated, along with the populations of the relevant traps and centers. Several experimentally observed characteristics of the RL signals were explained using the model.

Zero‐Dimensional Gua3SbCl6 Crystals as Intrinsically Reabsorption‐Free Scintillators for Radiation Detection

AbstractThe search for efficient, re‐absorption‐free scintillators has recently focused the attention on antimony‐based halides, which exhibit largely Stokes shifted luminescence due to radiative recombination of excitons self‐trapped (STE) in strongly Jahn–Teller distorted Sb3+ color centers. Here, the synthesis of a hybrid structure is reported with chemical formula (C13H14N3)3SbCl6 consisting of spatially isolated [SbCl6]3− octahedra separated by organic N,N'‐diphenylguanidinium (Gua) molecules. The optical properties of this material are mainly determined by the inorganic component and are characterized by a pronounced Stokes shift of ≈1.3 eV and a room‐temperature photoluminescence (PL) efficiency of up to 85%. Remarkably, highly efficient radioluminescence (RL) is observed with scintillation light yields of ≈2000 ph MeV−1 using both soft X‐rays and a 124 keV gamma source. Temperature‐dependent PL and RL measurements confirm the minor role of non‐radiative channels, which are completely suppressed below 100 K. Thermally stimulated luminescence measurements suggest that the traps in Gua3SbCl6 crystals have a significantly large energy depth distribution below the absorbing state.

Scintillator‐oriented near‐infrared emitting Cs4SrI6:Yb2+, Sm2+ single crystals via sensitization strategy

AbstractIn this study, a new Cs4SrI6:Yb2+,Sm2+ near‐infrared (NIR) emitting scintillator was developed using sensitization strategy. It was found that Yb2+ sensitization significantly enhances the NIR radioluminescence (RL) of Sm2+, providing a new approach of designing highly emissive sensitized NIR scintillators. By studying the optical spectra and decay kinetics of Cs4SrI6:Yb2+,Sm2+, it was revealed that the energy transfer pathways involve both radiative and nonradiative processes. The gamma spectroscopy performance of Cs4SrI6:Yb2+,Sm2+ single crystals was studied by using the high‐quantum‐efficiency avalanche photodiode (APD) as the readout. Our results highlight the importance of using sensitization strategy of achieving NIR emitting scintillators and demonstrate the significant potential for radiation detection applications.