The Study of Tunable Excitation Independent and Dependent Photoluminescence Behaviour of P-Functionalized Carbon Dots

In this article, excitation independent and dependent fluorescence properties of surface functionalized carbon dots were studied. The samples were synthesized using a biomass derived Indian gooseberry as carbon precursor via microwave irradiation technique. Concentrated phosphonic acid is utilized as a surface passivator for carbon dots. The formation of spherical carbon dots in the size range of 6 to 12 nm was shown by transmission electron microscopy images. Raman and Fourier transform IR spectroscopies suggest the creation of highly disordered sp 3 carbon atoms including presence of surface functional groups and interaction of phosphorus with surface of carbon core. From the UV-visible absorption study, absorbance bands at 231 nm and 283 nm attributed to π-π* molecular transitions from carbon core are found. From the photoluminescence measurements, both excitation independent and excitation dependent tunable fluorescence is obtained from ultraviolet to visible (yellow) region of light respectively. The involvement of carbon core electronic states and surface modifier states are responsible for the origin of luminescence and their distinguished nature. The mechanism is discussed and emitted colour are confirmed by CIE plot. The relative quantum yield of the P-functionalized carbon dots is found to be 18.9% with reference to quinine sulfate. The fluorescence in ultra-violet and visible regions is applicable for bioimaging and potential antimicrobial activities.