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Thermally activated delayed fluorescence (TADF) organic molecules for efficient X-ray scintillation and imaging

Nature Materials volume 21, pages 210–216 (2022)Cite this article

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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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Fig. 1: Mechanism illustrations and molecular structures of organic scintillators.
Fig. 2: Highly efficient RL and low self-absorptions of the TADF-based scintillators.
Fig. 3: Performance characterizations of organic scintillators.
Fig. 4: Highly resolved X-ray imaging based on TADF scintillators.

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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.

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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).

Author information

Author notes

  1. These authors contributed equally: W. Ma, Y. Su.

Authors and Affiliations

  1. State Key Laboratory of Modern Optical Instrumentation, Institute for Advanced Photonics, College of Optical Science and Engineering, Zhejiang University, Hangzhou, China

    Wenbo Ma, Yirong Su, Wenjuan Zhu, Yue Tian, Peng Ran, Tianyu Liu, Huafeng Liu, Xu Liu & Yang Michael Yang

  2. Intelligent Optics & Photonics Research Center, Jiaxing Institute of Zhejiang University, Jiaxing, China

    Wenbo Ma, Huafeng Liu & Yang Michael Yang

  3. MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, China

    Qisheng Zhang & Chao Deng

  4. Dipartimento di Ingegneria E. Ferrari, Università di Modena e Reggio Emilia, Modena, Italy

    Luca Pasquali

  5. CNR-IOM, Basovizza, Trieste, Italy

    Luca Pasquali

  6. Department of Physics, University of Johannesburg, Auckland Park, South Africa

    Luca Pasquali

  7. State Key Laboratory of Modern Optical Instrumentation, Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou, China

    Zeng Chen & Haiming Zhu

  8. Hubei Key Laboratory of Low Dimensional Optoelectronic Materials and Devices, Hubei University of Arts and Science, Xiangyang, China

    Gaoyuan Yang & Guijie Liang

  9. MIIT Key Laboratory for Low Dimensional Quantum Structure and Devices, School of Materials & Engineering, Beijing Institute of Technology, Beijing, China

    Peng Huang & Haizheng Zhong

  10. State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Center of Smart Materials and Devices, Wuhan University of Technology, Wuhan, China

    Kangwei Wang, Shaoqian Peng & Jianlong Xia

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  1. Wenbo Ma
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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.

Corresponding author

Correspondence to Yang Michael Yang.

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Peer review information Nature Materials thanks Beatrice Fraboni and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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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).

Source data

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).

Source data

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).

Source data

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.

Source data

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).

Source data

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

Source Data Fig. 2

Source Data for Figs. 2a,2b and 2d.

Source Data Fig. 3

Source Data for Fig. 3.

Source Data Fig. 4

Source Data for Fig. 4c.

Source Data Extended Data Fig. 3

Source Data for Extended Data Fig. 3.

Source Data Extended Data Fig. 4

Source Data for Extended Data Fig. 4.

Source Data Extended Data Fig. 5

Source Data for Extended Data Fig. 5b-d.

Source Data Extended Data Fig. 6

Source Data for Extended Data Fig. 6.

Source Data Extended Data Fig. 7

Source Data for Extended Data Fig. 7.

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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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