Direct in Situ Fabrication of Multicolor Afterglow Carbon Dot Patterns with Transparent and Traceless Features via Laser Direct Writing.

Multicolor afterglow patterns with transparent and traceless features are important for the exploration of new functionalities and applications. Herein, we report a direct in situ patterning technique for fabricating afterglow carbon dots (CDs) based on laser direct writing (LDW) for the first time. We explore a facile step-scanning method that reduces the heat-affected zone and avoids uneven heating, thus producing a fine-resolution afterglow CD pattern with a minimum line width of 80 µm. Unlike previous LDW-induced luminescence patterns, the patterned CD films are traceless and transparent, which is mainly attributed to a uniform heat distribution and gentle temperature rise process. Interestingly, by regulating the laser parameters and CD precursors, an increased carbonization and oxidation degree of CDs could be obtained, thus enabling time-dependent, tunable afterglow colors from blue to red. In addition, we demonstrate their potential applications in the in situ fabrication of flexible and stretchable optoelectronics.

Mechanical Force-Induced Color-Variable Luminescence of Carbon Dots in Boric Acid Matrix.

Mechano-luminescent materials that exhibit distinct luminescence responses to force stimuli are urgently anticipated in view of application needs in the fields of sensing, anti-counterfeiting, optoelectronic devices, etc. However, most of the reported materials normally exhibit force-induced changes in luminescent intensity, whereas materials that possess force-induced color-variable luminescence remain rarely reported. Herein, for the first time, a novel mechanical force-induced color-variable luminescence material from carbon dots (CDs) in boric acid (CD@BA) is reported. At low CDs concentration, the luminescence of CD@BA exhibits a grinding-induced color variable from white to blue. This grinding-induced color variable can be switched to yellow-to-white changing by increasing the CDs concentration in BA. The grinding-induced color-variable luminescence originates from dynamic variation in emission ratio of fluorescence and room temperature phosphorescence, due to the influence of oxygen and water vapor in the air. At high CDs concentration, short-wavelength fluorescence undergoes more severe reabsorption compared to room temperature phosphorescence, leading to grinding-induced color-variable switching from white-to-blue to yellow-to-white. Based on the unique properties of CD@BA powder, the applications of recognizing and visualizing fingerprints on the surfaces of various of materials are demonstrated.

Carbon Dots-Inked Paper with Single/Two-Photon Excited Dual-Mode Thermochromic Afterglow for Advanced Dynamic Information Encryption.

Achieving thermochromic afterglow (TCAG) in a single material for advanced information encryption remains a significant challenge. Herein, TCAG in carbon dots (CDs)-inked paper (CDs@Paper) is achieved by tuning the temperature-dependent dual-mode afterglow of room temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF). The CDs are synthesized through thermal treatment of levofloxacin in melting boric acid with postpurification via dialysis. CDs@Paper exhibit both TCAG and excitation-dependent afterglow color properties. The TCAG of CDs@Paper exhibits dynamic color changes from blue at high temperatures to yellow at low temperatures by adjusting the proportion of the temperature-dependent TADF and phosphorescence. Notably, two-photon afterglow in CDs-based afterglow materials and time-dependent two-photon afterglow colors are achieved for the first time. Moreover, leveraging the opposite emission responses of phosphorescence and TADF to temperature, CDs@Paper demonstrate TCAG with temperature-sensing capabilities across a wide temperature range. Furthermore, a CDs@Paper-based 3D code containing color and temperature information is successfully developed for advanced dynamic information encryption.