Down-Conversion Fluorescence Study of Non-metal Co-doped Carbon Dots

In this work, a down-conversion fluorescence study of carbon dots is presented. A facile microwave irradiation route is used to prepare the carbon dots by carbonization of citrus limetta juice in an aqueous medium. Phosphonic acid and ethylenediamine are taken as initial phosphorus (P) and nitrogen (N) sources, respectively. The optical and photoluminescence properties are investigated with different ratios of P to N. UV–Visible absorption spectroscopy and Raman spectroscopy are employed for the optical study. Fluorescence spectra are noted by spectrofluorometer in various excitation wavelengths. The observed absorbance peaks in the ultraviolet region represent n and π molecular transitions. The molar ratio of P to N modifies the electronic transitions. From PL spectra, the excitation-dependent emission spectra are observed. The enhanced down-conversion fluorescence in the green to the red region is blue-shifted with changing initial P/N ratio in carbon dots. The change in emission color with P/N is observed due to changes in emitting states and electronic transitions.