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We report the rational design of the matrix‐free carbon dots (C‐dots) with long wavelength and wavelength‐tunable room‐temperature phosphorescence (RTP). Taking advantage of microwave‐assisted heating treatment, three RTP C‐dots in boric acid (BA) composites are synthesized by using diethylenetriaminepentakis (methylphosphonic acid) as a multiple‐sites crosslink agent, a moderately acid catalyst and P source; phenylenediamines (either o‐PD, m‐PD, or p‐PD, respectively) as building block while BA as a carbonization‐retardant matrix. After the water‐soluble BA matrix is removed by dialysis, three matrix‐free C‐dots are obtained with RTP emission at 540, 550 and 570 nm under an excitation wavelength of 365 nm. Alterations of RTP emission of three matrix‐free C‐dots are ascribed to the difference in their particle size and band gap from n‐π* transition. Furthermore, the application of three matrix‐free C‐dots are successfully performed in information encryption and decryption. [ABSTRACT FROM AUTHOR]

Multiple-color emissive carbon dots (C-dots) are gaining increasing attention in various fields. Herein, we report a facile solvothermal method for the synthesis of multiple-color emissive C-dots with the aim of white-light emission. Under single ultraviolet-light excitation, three C-dots emit a easily controlled fluorescent emission wavelength at 440 nm, 500 nm and 610 nm by using different three amines (either ammonium hydroxide, ethylenediamine or p-phenylenediamine, respectively) and pyromellitic dianhydride as molecular precursors while another three C-dots emit a controllable fluorescent emission wavelength at 500 nm, 550 nm and 585 nm by using same three amines and naphthalene-1,4,5,8-tetracarboxylic dianhydride as molecular precursors. The maximum fluorescence wavelength of these C-dots is red-shifted by changing three different amines molecular precursors from ammonium hydroxide, ethylenediamine, to p-phenylenediamine. Furthermore, these C-dots have shown promising applications in the fields of white-light-emitting diodes devices and color printing. [ABSTRACT FROM AUTHOR]