Abstract
X-ray detection, which plays an important role in medical and industrial fields, usually relies on inorganic scintillators to convert X-rays to visible photons; although several high-quantum-yield fluorescent molecules have been tested as scintillators, they are generally less efficient. High-energy radiation can ionize molecules and create secondary electrons and ions. As a result, a high fraction of triplet states is generated, which act as scintillation loss channels. Here we found that X-ray-induced triplet excitons can be exploited for emission through very rapid, thermally activated up-conversion. We report scintillators based on three thermally activated delayed fluorescence molecules with different emission bands, which showed significantly higher efficiency than conventional anthracene-based scintillators. X-ray imaging with 16.6 line pairs mm−1 resolution was also demonstrated. These results highlight the importance of efficient and prompt harvesting of triplet excitons for efficient X-ray scintillation and radiation detection.
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Data availability
The source data related to the main figures and extended data figures are provided with this manuscript. Further data are available from the authors upon request. Source data are provided with this paper.
Change history
04 March 2022
A Correction to this paper has been published: https://doi.org/10.1038/s41563-022-01226-0
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Acknowledgements
We thank S. Deng and S. Yao of Hamamatsu Photonics for their assistance with X-ray-related measurements and useful discussions, and B. Yang and H. Liu of Jilin University and Y. Zhang of Huzhou Normal University for assistance with material preparations. Y.(M.)Y. acknowledges funds received from the National Key Research and Development Program of China (2017YFA0207700), the Outstanding Youth Fund of Zhejiang Natural Science Foundation of China (LR18F050001) and the Natural Science Foundation of China (62074136, 61804134, 61874096).
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Contributions
Y.(M.)Y. conceived the idea and designed the experiments. W.M. and Y.S. prepared the scintillator molecules, characterized the performance and conducted the X-ray-related experiments. W.M. derived the mathematical model to quantify the X-ray-induced photoexcitation. Y.(M.)Y., W.M. and Y.S. analysed the results. Q.Z. and C.D. provided insightful discussions on the photophysics and chemistry of the TADF mechanism and provided some TADF molecules for the study. L.P. provided insightful discussions on the mechanism of X-ray interactions with organic molecules. C.D., Z.C. and H.Zhu. helped with lifetime measurements, and participated in helpful discussions. P.H., W.Z., Y.S. and H.Zhong. synthesized the CsPbBr3 NCs. Y.T., P.R. and T.L. assisted with X-ray imaging measurements. G.Y., G.L., K.W., S.P. and J.X. helped with the transient absorption measurements. X.L. and H.L. provided insightful discussions on optical system design. W.M. plotted the data and prepared the figures. Y.(M.)Y. wrote the manuscript with input from W.M. and Y.S.
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Extended data
Extended Data Fig. 1 Measurement set-up of the RL intensities of organic scintillators.
Schematic of the testing system for radioluminescence (RL) intensity measurement.
Extended Data Fig. 2 HOMO and LUMO of organic scintillators.
Highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) according to the results of time-dependent DFT for the S1 states of Anthracene, DMAc-TRZ, 4CzIPN and 4CzTPN-Bu using the optimized structure of the S0 states. Colors indicate the different phases of the natural transition orbitals.
Extended Data Fig. 3 Normalized RL spectra of organic scintillators when thickness increasing.
Normalized RL spectra at the thicknesses of 0.1, 0.2, 0.4 and 0.8 mm of a, Anthracene, b, DMAc-TRZ, c, 4CzIPN and d, 4CzTPN-Bu, respectively. (X-ray tube voltage: 50 kV; dose rate: 3.034 mGyair s-1).
Extended Data Fig. 4 Normalized PL and PLE spectra of organic scintillators.
The normalized photoluminescence (PL, solid lines) spectra and the normalized photoluminescence excitation (PLE, dotted lines) spectra of DMAc-TRZ, 4CzIPN and 4CzTPN-Bu in toluene (left) compared with that of Anthracene in toluene (right).
Extended Data Fig. 5 X-ray attenuation efficiency spectra of organic scintillators and output spectra of X-ray tube.
a, Output spectra at different tube voltages of Mini-X X-ray tube (target: Ag, characteristic peak is at 22 keV). b, Calculated X-ray attenuation efficiencies of Anthracene, DMAc-TRZ, 4CzIPN, 4CzTPN-Bu and sucrose octaacetate (SO) versus thicknesses of these scintillators. c, Calculated X-ray attenuation coefficient (cm-1) spectra of Anthracene, DMAc-TRZ, 4CzIPN, 4CzTPN-Bu and SO, respectively. d, Calculated X-ray attenuation efficiency spectra of Anthracene, DMAc-TRZ, 4CzIPN, 4CzTPN-Bu and SO at thickness of 400 μm (the thickness value for calculation of light yield).
Extended Data Fig. 6 RL intensity spectra of the diluted organic scintillator screens.
RL intensity spectra of 10 wt% Anthracene:SO screen, 10 wt% DMAc-TRZ:SO screen, 10 wt% 4CzIPN:SO screen and 10 wt% 4CzTPN-Bu:SO screen.
Extended Data Fig. 7 RL linear relationships of TADF organic scintillators.
The RL intensities versus biggish X-ray dose rates of DMAc-TRZ, 4CzIPN and 4CzTPN-Bu, respectively. The error bars were determined by the measurements of three samples and each sample was measured three times. It can be obviously observed that these TADF organic scintillators show good linear relationships between RL intensity and X-ray dose rate. (X-ray tube voltage: 50 kV, current: 79 μA).
Extended Data Fig. 8 Photographs and X-ray images of TADF organic scintillator screens.
a-c, Photographs under a, bright field, b, ultraviolet illumination and c, X-ray irradiation of 10 wt% DMAc-TRZ:SO scintillator screen, 10 wt% 4CzIPN:SO scintillator screen and 10 wt% 4CzTPN-Bu:SO scintillator screen, respectively. d, X-ray images of encapsulated metallic spring collected by 10 wt% DMAc-TRZ:SO scintillator screen, 10 wt% 4CzIPN:SO scintillator screen and 10 wt% 4CzTPN-Bu:SO scintillator screen, respectively. (X-ray tube voltage: 50 kV; dose rate: 75.5 μGyair s-1).
Supplementary information
Supplementary Information
Supplementary Discussions 1–3, Figs. 1–11 and Tables 1–5.
Supplementary Video 1
Comparison of RL performances among three TADF scintillators and anthracene.
Supplementary Video 2
PL and RL performances of CsPbBr3 QDs and DMAc-TRZ.
Source data
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Ma, W., Su, Y., Zhang, Q. et al. Thermally activated delayed fluorescence (TADF) organic molecules for efficient X-ray scintillation and imaging. Nat. Mater. 21, 210–216 (2022). https://doi.org/10.1038/s41563-021-01132-x
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DOI: https://doi.org/10.1038/s41563-021-01132-x
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