Temperature-responsive conversion of thermally activated delayed fluorescence and room-temperature phosphorescence of carbon dots in silica

Abstract

The unique temperature-responsive afterglow characteristics of CDs was reported for the first time, which can meet multiple potential applications in rapid fingerprint detection, temperature sensing, and advanced temperature-responsive anti-counterfeiting and encryption.

Afterglow Carbon Dots: From Fundamentals to Applications

“…The high reversibility is an outcome of the intact of the intrinsic attributes of the CDs during the experiment (Figure 8(g)). Similar results were observed from CDs@SiO 2 nanocomposites by Sun and coworkers in 2020 (Figures 8(h) and 8(i)) [97]. Though the temperature-responsive afterglow luminescence of CDs can add considerable versatility in their applications, rational synthesis of CDs with a controlled combination of RTP and TADF is still a formidable challenge.…”

“…The dependence of the afterglow luminescence of CDs on temperature and excitation wavelength can also be harnessed to fabricate multiple color codes for anticounterfeiting [84,97]. In 2020, Sun et al made a pattern with the use of CDs@SiO 2 as security ink and found that the pattern is presented in bright blue under excitation at 365 nm (Figure 11(f)) [97]. Once the excitation was terminated, a color transition of the pattern from blue to green was observed, and the resulting green afterglow pattern can last for a few seconds.…”

“…(i) Normalized RTP and TADF emission intensity as a function of temperature (excitation at 365 nm). Inset: typical afterglow color output originating from RTP (green) and TADF (blue) (adapted and copyright permission[97] (h, i), Royal Society of Chemistry). (j) Schematic energy level diagrams showing the generation of a new triplet state (T * ) as a result of the aggregation of CDs.…”

Luminescence anti‐counterfeiting: From elementary to advanced

“…The triple emissions co‐regulated by mechanical stimuli, UV irradiation, and luminescence lifetime accomplished three‐level luminescence anti‐counterfeiting process. Moreover, excitation light, heat stimuli together with chemical reagents, [ 111,115 ] or excitation light, heat stimuli together with luminescence lifetime, [ 109,110,114,116,118 ] or excitation light, luminescence lifetime together with chemical regents, [ 107,108,112,117,119 ] or excitation light, heat stimuli, luminescence lifetime together with mechanical stimuli, etc., [ 120 ] can also be simultaneously adopted to realize multilevel luminescence anti‐counterfeiting. As displayed in Figure 8C, it is a typical luminescence anti‐counterfeiting co‐regulated by four kinds of factors.…”

“…Based on the category of regulation factors, multilevel luminescence anti‐counterfeiting can be divided into five types: (1) regulated by excitation light; [ 64–80 ] (2) co‐regulated by excitation light and luminescence lifetime; [ 81–92 ] (3) co‐regulated by excitation light and heat stimuli; [ 35,63,93–96 ] (4) co‐regulated by excitation light and chemical reagents; [ 16,97–105 ] and (5) co‐regulated by other factors. [ 106–121 ]…”