Long-wavelength orange-red emissions of carbon dots have recently attracted great attention due to their wide applications. Although it is possible to achieve long-wavelength luminescence by varying the incident excitation wavelength, excitation-independency is highly desired in terms of both practical applications and understanding emission mechanisms. In the present work, carbon dots with excitation wavelength independent orange and blue dual-color emissions were synthesized by a facile solvothermal route using p-phenylenediamine as carbon source and formamide as solvent. Structural and spectroscopic characterizations indicated that N-and O-related surfacestate controlling via modifying reacting temperature/time was responsible for the dual-color emissions of carbon dots. Moreover, carbon solid film, retaining original orange emissions, was fabricated to explore its possible application as color converter in solidstate lighting. Impressively, by combining orange carbon film and yellow phosphor-in-glass with an InGaN blue chip, lightemitting diode devices with improved color-rendering index and correlated color temperature were successfully constructed.

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a 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 pphenylenediamine 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.

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