Guiding the Triplet Excited State Landscape in Host‐Confined Carbon Dots by Orbital Mismatch

Abstract Long persistence luminescence is deeply intriguing to the scientific community because of its widespread application in “glow‐in‐the‐dark” paints. These materials capture excitation energy and release it gradually as light. Achieving stable triplet excitons in carbon dots (CDs) without using heavy elements is quite challenging. Successful synthesis of two types of CDs using salicylic (SA) and thiosalicylic acid (TSA) is reported as precursors in boric acid (BA) matrix with acronym SA@BA and TSA@BA having photoluminescence quantum yield (PLQY) of 68% and 38%, and average lifetime of 870 and 340 ms, respectively, with a substantial afterglow. It is noticed that the glassy BA matrix modulates the afterglow of the CDs through multilayered confinement. Overlapping of the oxygen and boron orbitals in SA@BA aligns the triplet energy states very closely, resulting in excitation‐dependent phosphorescence unaffected by the delay time. In contrast, TSA@BA exhibits phosphorescence that varies with both excitation wavelength and delay time, a behavior attributed to the orbital mismatch between sulfur and boron. The obtained results are applied in formulating a “Morse code” based multilayer anti‐counterfeiting security arrangement, which can be very simply operated to get significant output.