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.

    Abstract
    1 Introduction
    2 Experimental
        2.1 Preparation
        2.2 Characterization
    3 Results and discussion
        3.1 Appearance of PG-CDs as powders and aqueous solutions, and the photoluminescence performance
        3.2 TG-DSC
        3.3 Elemental analysis and XPS
        3.4 PL properties
        3.5 Molecular weights and sizes of PG-CDs
        3.6 XRD
        3.7 NMR
        3.8 pH stability test and zeta potential
        3.9 Estimated structures
    4 Conclusions
    References

• Syun Gohda(Nippon Shokubai Co., Ltd.)
• Hironobu Ono(Nippon Shokubai Co., Ltd.)
• Yasuhiro Yamada(Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University)