Carbon dots (CDs) were synthesized from phloroglucinol (PG) by simple heat treatment at 220–230 °C in the atmosphere without catalysts and solvents. PG-CDs heated at 220–230 °C could be completely dissolved in environmentally friendly water and exhibited a photoluminescence (PL) peak at 485 nm with 85 nm of the full width at half maximum (FWHM). The water-soluble polymer-dot-like PG-CDs were estimated to be 1.6–3.2 nm in size, and exhibited a wide range of PL wavelength at 370–630 nm. Since the PG-CDs are water-soluble materials, PG-CDs could be homogeneously mixed with a polymer such as polyvinylpyrrolidone (PVP) in water as a solvent, and PG-CDs/PVP films were prepared. The films exhibited PL characteristics that convert ultraviolet light at 350 nm to visible light above 400 nm. Thus, using PG as the raw material which has widely been produced industrially, the water-soluble fluorescent PG-CDs/PVP films could be prepared at a low cost by environmentally friendly methods.

Nitrogen-doped carbon dots (CDts) with tunable fluorescence properties in aqueous media were synthesized hydrothermally. The excitation wavelength variation to obtain the maximum emission produced a blue shift in the emission peaks upon dilution in an aqueous solution. The shift can be explained by a re-absorption phenomenon in a concentrated solution. The interparticle interaction within was responsible to show dilution-dependent optical behavior. The as-synthesized solution of CDts did not show any prominent absorption peak over a wide range. However, upon dilution, two peaks became predominant. The concentration-dependent behavior was observed during the interaction with metal cations. Cationic salts of Co(II) and Hg(II) caused quenching at different dilutions of CDts. This might be explained by the exposure of different surface functional groups during dilution and metal-ion–CDts charge transfer. The quenched fluorescence of CDts was rescued using ascorbic acid. Therefore, the one-pot detection of Co(II)/Hg(II) and ascorbic acid was designed through a ‘Turn Off/On’ phenomenon.

The thermoelectric Seebeck and Peltier effects of a single walled carbon nanotube (SWCNT) quantum dot nanodevice are investigated, taking into consideration a certain value of applied tensile strain and induced ac-field with frequency in the terahertz (THz) range. This device is modeled as a SWCNT quantum dot connected to metallic leads. These two metallic leads operate as a source and a drain. In this three-terminal device, the conducting substance is the gate electrode. Another metallic gate is used to govern the electrostatics and the switching of the carbon nanotube channel. The substances at the carbon nanotube quantum dot/ metal contact are controlled by the back gate. Results show that both the Seebeck and Peltier coefficients have random oscillation as a function of gate voltage in the Coulomb blockade regime for all types of SWCNT quantum dots. Also, the values of both the Seebeck and Peltier coefficients are enhanced, mainly due to the induced tensile strain. Results show that the three types of SWCNT quantum dot are good thermoelectric nanodevices for energy harvesting (Seebeck effect) and good coolers for nanoelectronic devices (Peltier effect).