Temperature- and pH-modulated Förster resonance energy transfer for establishment of white light emission

Heteroatom doping is an efficient approach for increasing fluorescence efficiency of carbon dots (CDs). Co-doping with heteroatoms may add additional active sites to CDs and expand their different capabilities. A simple and low-cost hydrothermal method was used to prepare nitrogen- and also nitrogen- and sulfur-rich CDs-decorated graphene oxide, NCDs-GO and N,SCDs-GO, respectively. The as-prepared hybrid CDs-GO samples are responsive to pH and temperature variations, implying pH and temperature-dependent fluorescence properties. The different properties of the CDs-GO hybrids were investigated using transmission electron microscopy and also energy-dispersive X-ray, Raman, and Fourier transform infrared spectroscopies. The ternary mixture of N,SCDs-GO, poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), and rhodamine B (RB) was also used to detect pH changes via the Förster resonance energy transfer (FRET) process, where N,SCDs-GO and RB play the role of donor and acceptor, respectively, in the PDMAEMA aqueous solution medium. Fluorescence and ultraviolet–visible spectroscopies were used to assess the feasibility and efficiency of the FRET process. The donor–acceptor ratio was changed to get the broadly adjustable photoluminescence emission from blue to red, and especially white light. The aqueous ternary mixture has a wide range of potential applications in pH sensing, temperature monitoring, and anticounterfeiting. This colloidal system with controllable fluorescence and white light emission was used to design anticounterfeiting inks for security-marking of wood samples.