Red C-dots and C-dot films: solvothermal synthesis, excitation-independent emission and solid-state-lighting

Currently, fluorescent carbon dots (CDs) have attracted great attention for their unique optical performance. However, the shortage of red emissive CDs and the corresponding CD solid samples with intense luminescence significantly limit their applications in optoelectronic fields. In the present work, red fluorescence CDs were successfully synthesized via a facile solvothermal reaction using p-phenylenediamine as the carbon source and isopropanol as the solvent. Excitation-independent luminescence and emission-independent decay indicated that one dominant type of emissive state was responsible for red luminescence, which was evidenced to be a N-related surface defect state with the help of structural and spectroscopic characterizations. Furthermore, CD-embedded PVA solid films, exhibiting bright red emission with intense absorption in the blue-light region, were prepared to explore their possible application as a color converter in solid-state lighting. As a proof-of-concept experiment, white light-emitting diode devices were constructed by combining a red CD solid film and yellow Ce:YAG phosphor-in-glass with a commercial InGaN blue chip, showing tunable color coordinates, color rendering index and correlated color temperature via modifying the thickness of the CD film.