Excitation-independent carbon dots, from photoluminescence mechanism to single-color application

Abstract

Carbon dots (Cdots) have attracted much interest recently because of their extraordinary and tunable optical properties. However, the poor understanding of their photoluminescence (PL) mechanism limited the universality of Cdots. In this paper, we prepared the raw-Cdots via a facile hydrothermal method; Green- and Blue-Cdots were obtained from the raw-Cdots as they showed excitation-independent green and blue PL emission. The photoluminescence mechanism was therefore studied with the two kinds of single-color Cdots. Two kinds of Cdots have almost the same element contents but different oxygen- and nitrogen-containing groups. The excitation-independent PL mechanism of Cdots was proposed in combination with their optical properties and surface groups. The π-conjugated electron system acts as the center for quantum confinement and photo absorption, surface groups provide different vibration relaxation for their excitation-independent emission and large Stokes shift. This study not only provides the excitation-independent PL mechanism but also shows the insightful guidance for fluorescence applications of Cdots with excitation-independent PL. Given their complementary emission and excitation wavelength properties, the single color fluorescence from Green-Cdots and Blue-Cdots were used for doubly encrypted characters.