Presently, the doping of nano-carbons with the heteroatoms and metal-salts as an external dopant is a common practice for articulating the optical applicative efficiency especially of the carbon dots (CD). The ease in the fabrications of the self-doped CD could be a taken as a sustainable approach, where the additions of the external dopant material can either be avoided or minimized. It may refer to the use of biomaterials like plant leaves, as they already possessed the metals inside as an essential element. A simpler process of the carbonization of leave extract can yield the red emitting magnesium-nitrogen embedded (self-doped) CD as “r-Mg-N-CD” possessing the quantum yield value of ~ 41 %. Importantly, r-Mg-N-CD were proven to be a biocompatible probe concerning its nontoxic behavior based on the bacteriological test performed on the two different bacterial strains; Escherichia coli (E.coli) and Proteus vulgaris (P.vulgaris). In addition to the conventional imaging application, these r-Mg-N-CD can also be used for the fluorescence-based selective sensing of Cu (II) metal ion out of many tested heavy metals with the detection limit as low as 50 nM and also as red-emitting fluorescent ink.
The reported finding shows a simpler way for the synthesis of the red emitting self-doped r-Mg-N-CD via the utilization of biomaterials as the leaves in an economical (without using any external reagent) method. The as produced red emitting r-Mg-N-CD showed the high quantum yield values. Based on the bacteriological test, r-Mg-N-CD are nontoxic on the two different types of bacterial strains: E. coli and P. vulgaris and being used for the imaging of these cells. As well as, these red emitting r-Mg-N-CD is further being used for fluorescence based selective sensing of Cu(II) metal ion out of many tested different metal ions Ba(II), Sr(II), Co(II), Ni(II), Zn(II), Bi(II), Hg(II), Al(III), and Cr(VI) in the aqueous solution with LOD in the range of nano molar. Along with these, r-Mg-N-CD can be also used as a red-emitting biocompatible fluorescent ink.

A straightforward and simpler use of an age-old technique was utilized for the fabrication of “red-emitting magnesium-nitrogen-embedded carbon dots” (r-Mg-N-CD) from the leaves extract of Bougainvillea plant as a natural source of carbon. This technique is similar to the solvent-based technique, which is used for the extraction of fragrances and essential oils from flowers and leaves. The as-derived leaves extract was further carbonized using a simple domestic microwave to obtain the small-sized red-emitting carbonaceous material as r-Mg-N-CD. The r-Mg-N-CD showed excitation independent emissions at ∼678 nm with excellent photostability and a high quantum yield value (∼40%). Moreover,the important perspective of the present finding is to use this r-Mg-N-CD as a potential photocatalyst material for the degradation of pollutant dye (methylene blue) under the presence of sunlight. To infer the significant influence of using natural sunlight in the process of dye degradation, a comparative analysis was performed, demonstrating the higher rate of photo degradation (∼6 times faster) under the influence of sunlight compared to the artificial visible-light from a 100 W tungsten bulb.
The present finding describes here discusses the possibilities for fabricating low-cost, high-quantum-yield, red-emitting r-Mg-NCD in an environment-friendly (without using any externally added chemical reagent). Red-emitting r-Mg-N-CD was used as a novel photocatalytic material for the aqueous phase photodegradation of MB under the presence sunlight. The vast potential of sunlight explored was compared with an artificial tungsten bulb by the use of r-Mg-N-CD, which showed many folds of increase in the rate of photodegradation under the influence of sunlight. Higher in value of quantum yield, solubility in aqueous media, and emission in the red wavelength region along with the ability to photodegrade the pollutant dyes within the ∼120 min of sunlight irradiation, makes r-Mg-N-CD a potential nanomaterial for its applications in the field of aqueous-phase photodegradation. As well, the embedded Mg can also been replaced from some other metal for enhancing its optical properties.