Solid‐State, Hectogram‐Scale Preparation of Red Carbon Dots as Phosphor for Energy‐Transfer‐Induced High‐Quality White LEDs with CRI of 97

In this study, pre‐crystallization‐controlled, solid‐state preparation of red carbon dots (C‐dots) from o‐phenylenediamine on a hectogram scale with a 94% yield is reported. Highly efficient red phosphor (C‐dots@MCC) is obtained by dispersing the C‐dots in microcrystalline cellulose, which matched extremely well with the commercial Y3Al5O12:Ce3+ (YAG) phosphor. White light‐emitting diodes (WLEDs) fabricated from the two phosphors emitted warm white light with a correlated color temperature of 3845 K, CIE color coordinates of (0.38, 0.37), and an extremely high color rendering index (CRI) of 95, outperforming all the reported YAG‐derived WLEDs. Furthermore, the CRI value of the WLED can be further increased to 97 after fine‐tuning, which is the highest CRI for WLEDs of any C‐dots derived devices reported so far. The superior performance of the WLED is attributed to a delicate energy transfer between YAG and C‐dots@MCC. Most importantly, the WLED maintained excellent stabilities under varied currents, working durations, moistures, and temperatures. This article presents a pre‐crystallization‐tuned direct calcination method to prepare hundred‐gram scale red‐emissive carbon dots (C‐dots). The C‐dots are dispersed in microcrystalline cellulose as red phosphor. Efficient energy transfer between the red phosphor and commercial yellow Y3Al5O12:Ce3+ (YAG) fluorescent powder renders the fabrication of warm white light‐emitting diodes (WLEDs) with an extremely high color‐rendering index of 97.