Research ArticleMATERIALS SCIENCE

Carbon dots in zeolites: A new class of thermally activated delayed fluorescence materials with ultralong lifetimes

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Science Advances  26 May 2017:
Vol. 3, no. 5, e1603171
DOI: 10.1126/sciadv.1603171
  • Fig. 1 Proposed in situ formation process of photoluminescent CDs@AlPO-5 composite.

    The reaction mixture is composed of inorganic precursors and organic species. Under the solvothermal condition, the formation of CDs is accompanied with the crystallization of zeolite, and the CDs can be in situ embedded and confined in the zeolite matrix during the crystal growth, resulting in photoluminescent CDs@zeolite composite.

  • Fig. 2 SEM and TEM images and photoluminescence properties of CDs@zeolite composites.

    (A) Scanning electron microscopy (SEM) image of CDs@AlPO-5 composite (inset, the inorganic framework and the SDA). (B) TEM image of CDs@AlPO-5 composite showing CDs embedded in the inorganic matrix (inset, HRTEM image of a typical CD with a lattice spacing of 0.21 nm). (C) Excitation-emission two-dimensional plot of CDs@AlPO-5 composite. Emission intensity rises with the color changing from blue to green and to red. (D) Fluorescence microscopy images of CDs@AlPO-5 with ultraviolet (UV), blue, and green light excitation. (E to L) The SEM, TEM, HRTEM images, excitation-emission two-dimensional plots, and fluorescence microscopy images with UV, blue, and green light excitation of CDs@2D-AlPO and CDs@MgAPO-5, respectively.

  • Fig. 3 TADF properties of CDs@AlPO-5 composite.

    (A) The steady-state photoluminescence spectrum (deep blue line) and delayed photoluminescence spectrum (blue line) of CDs@AlPO-5 excited under 370 nm at room temperature. The emission band of the delayed fluorescence centers at 430 nm, which is consistent with that of the prompt fluorescence shown in the steady-state spectrum. Inset: The photographs of CDs@AlPO-5 under sunlight, excited with a UV lamp (365 nm) and then turned off. a.u., arbitrary units. (B) The time-resolved decay spectra of CDs@AlPO-5 at room temperature with the long lifetime of 350 ms and short lifetime (inset) of 2.9 ns. (C) Temperature-dependent transient photoluminescence decay of the CDs@AlPO-5 composite. (D) The steady-state photoluminescence spectrum (deep blue line) and delayed photoluminescence spectrum (olive line) of CDs@AlPO-5 excited under 370 nm at 77 K. The delayed photoluminescence spectra were collected with the delay time of 1 ms.

  • Fig. 4 Proposed TADF mechanism of CDs@zeolite composites and dual-responsive security protection application.

    (A) Left: CDs dispersed in the mother liquid show only the prompt fluorescence (PF) with short-lived lifetime. The triplet state would be quenched by nonradiative processes such as the active intramolecular vibrations (vib) and rotations. Right: The terminal OH groups of the interrupted zeolite framework, along with the occluded organic SDAs may form extensive H bonds with the surface functional groups of CDs to suppress the nonradiative relaxation of CDs derived from intramolecular vibrations and rotations and thus stabilize the triplet excited states. The small ΔEST value of the CDs makes it possible for an efficient TADF emission facilitated by the RISC process. P, phosphorescence. (B) The security pattern of a rose is coded with the CDs@2D-AlPO as the flower part and the benzil dye molecule as the leaf and stem parts. Under a 365-nm UV excitation, the flower patterned with CDs@2D-AlPO is blue, and the leaves and stem patterned with benzil dye molecules are green. When switching off the excitation, only the flower represents ultralong delayed fluorescence that can be clearly observed by naked eyes, showing the time-resolved security features.

  • Table 1 Photophysical characteristics of CDs@zeolite composites under ambient conditions excited at 370 nm.

    PL, photoluminescence.

    CompoundsPL (nm)CIEQYs (%)τTADF (ms)ΔEST (eV)
    CDs@AlPO-5430(0.17, 0.13)15.533500.22
    CDs@2D-AlPO440(0.17, 0.14)52.141970.23
    CDs@MgAPO-5425(0.17, 0.13)22.772160.22

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/5/e1603171/DC1

    fig. S1. PXRD patterns.

    fig. S2. LC-HRMS of dissolved CDs@AlPO-5 composite.

    fig. S3. The particle diameter distributions of CDs in CDs@zeolite composites.

    fig. S4. TEM analysis and photoluminescence property of CDs in the diluted mother liquid of CDs@AlPO-5.

    fig. S5. Structure of 2D-AlPO synthesized by using TTDDA as SDA.

    fig. S6. TADF properties of CDs@2D-AlPO composite.

    fig. S7. TADF properties of CDs@MgAPO-5 composite.

    fig. S8. TADF properties of CDs@zeolite composites after vacuum drying for 12 hours at room temperature.

    fig. S9. The compositional analysis of the organic species in CDs@AlPO-5 composite.

    fig. S10. The compositional analysis of the organic species in CDs@2D-AlPO composite.

    fig. S11. The compositional analysis of the organic species in CDs@MgAPO-5 composite.

    fig. S12. The time-resolved decay spectrum of the CDs in the diluted mother liquid of CDs@AlPO-5 at room temperature.

    fig. S13. PXRD and TG characterizations of CDs@AlPO-5 composites vacuum-calcined at different temperatures.

    fig. S14. TADF properties of CDs@AlPO-5 composites upon vacuum calcination at different temperatures.

    fig. S15. TADF properties of CDs@zeolite composites kept under ambient conditions for more than half a year.

    table S1. Crystal data and structure refinement for CDs@2D-AlPO.

    table S2. Atomic coordinates (× 104) and equivalent isotropic displacement parameters (Å2 × 103) for CDs@2D-AlPO.

    table S3. The photoluminescence emission bands and lifetimes of CDs@zeolite composites after vacuum drying at room temperature.

    table S4. The photoluminescence emission bands and lifetimes of CDs@AlPO-5 composites after vacuum calcination at different temperatures.

    table S5. The photoluminescence emission bands and lifetimes of CDs@zeolite composites before and after half a year under ambient conditions.

    table S6. The multiexponential lifetime (τi) and preexponential for lifetime (Ai) of the CDs@zeolite composites and the diluted mother liquid.

    data file S1. CIF file for CDs@2D-AlPO.

    data file S2. CheckCIF file for CDs@2D-AlPO.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. PXRD patterns.
    • fig. S2. LC-HRMS of dissolved CDs@AlPO-5 composite.
    • fig. S3. The particle diameter distributions of CDs in CDs@zeolite composites.
    • fig. S4. TEM analysis and photoluminescence property of CDs in the diluted mother liquid of CDs@AlPO-5.
    • fig. S5. Structure of 2D-AlPO synthesized by using TTDDA as SDA.
    • fig. S6. TADF properties of CDs@2D-AlPO composite.
    • fig. S7. TADF properties of CDs@MgAPO-5 composite.
    • fig. S8. TADF properties of CDs@zeolite composites after vacuum drying for 12 hours at room temperature.
    • fig. S9. The compositional analysis of the organic species in CDs@AlPO-5 composite.
    • fig. S10. The compositional analysis of the organic species in CDs@2D-AlPO composite.
    • fig. S11. The compositional analysis of the organic species in CDs@MgAPO-5 composite.
    • fig. S12. The time-resolved decay spectrum of the CDs in the diluted mother liquid of CDs@AlPO-5 at room temperature.
    • fig. S13. PXRD and TG characterizations of CDs@AlPO-5 composites vacuum-calcined at different temperatures.
    • fig. S14. TADF properties of CDs@AlPO-5 composites upon vacuum calcination at different temperatures.
    • fig. S15. TADF properties of CDs@zeolite composites kept under ambient conditions for more than half a year.
    • table S1. Crystal data and structure refinement for CDs@2D-AlPO.
    • table S2. Atomic coordinates (× 104) and equivalent isotropic displacement parameters (Å2 × 103) for CDs@2D-AlPO.
    • table S3. The photoluminescence emission bands and lifetimes of CDs@zeolite composites after vacuum drying at room temperature.
    • table S4. The photoluminescence emission bands and lifetimes of CDs@AlPO-5 composites after vacuum calcination at different temperatures.
    • table S5. The photoluminescence emission bands and lifetimes of CDs@zeolite composites before and after half a year under ambient conditions.
    • table S6. The multiexponential lifetime (τi) and preexponential for lifetime (Ai) of the CDs@zeolite composites and the diluted mother liquid.

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    Other Supplementary Material for this manuscript includes the following:

    • data file S1 (.CIF format). CIF file for CDs@2D-AlPO.
    • data file S2 (.pdf format). CheckCIF file for CDs@2D-AlPO.

    Download Data Files S1 and S2

    Files in this Data Supplement:

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