Photoluminescence Quenching in Metal Doped Graphitic Carbon Nitride: Possibilities Toward Metal Sensors

The present work describes the synthesis of graphitic carbon nitride (GCN) via simple two-step thermal decomposition of urea at a moderate temperature of 550 °C. The as-synthesized GCN is further doped with transition metals like nickel, and both the pure and doped GCN are characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), and Fourier transformed infrared (FTIR) spectroscopy. XRD shows the perfect phase formation in the pure GCN, which also remains in the doped sample but with much lesser crystallinity. FESEM shows that after doping, the small chips-like structure of GCN gets transformed to an elongated one. XPS confirms the successful doping by keeping the signature of both nickel 2P_1/2 and 2P_3/2 oxidation states in the spectra, whereas FTIR gave an idea about different bonding present in the sample. The pure sample, when irradiated with an excitation wavelength of 350 nm, gives an intense peak at 457 nm, which gets considerably quenched in the case of the doped sample. However, a new peak appears in the photoluminescence (PL) spectra of the doped sample at 624 nm. The quenching of PL intensity in the doped sample is assumed to be due to the fact that the dopant-induced state traps the electron, hindering them from immediate recombination. This quenching of PL intensity generates the possibilities of sensing the presence of different metals and thus taking measurable steps for removing them. The CIE chromaticity diagrams for the doped and undoped samples confirm that the emission color changes from blue to cyan region after the doping.