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It still remains a challenge to synthesize solid‐state carbon dots (CDs) with high emission efficiency; a hurdle that has hindered the application of CDs in many fields. In this work, efficient fluorescent CDs have been prepared through a one‐step microwave‐assisted heating method. Experimental data show strong green emissions produced from the CD powders (CDPs), carrying an unprecedented 75.9% quantum yield due to both spatial confinement and defect reduction with the introduction of NaOH. Likewise, CDPs prepared in tens of grams at 3 min time intervals also achieve high production yields at ≈69.8%. Specifically, for white light‐emitting devices (WLEDs) with color coordinates of 0.366 and 0.366, when fabricated by coating CDPs with commercial red‐emitting phosphors on blue‐emitting LED chips, it is found that the luminous efficiency reached 52.3 lm W−1. Besides, the WLEDs exhibit a high color rendering index of 93.5 and show great color chromatic stability even at a driving current of 200 mA. [ABSTRACT FROM AUTHOR]

It is still a challenging issue to achieve efficient and tunable fluorescent carbon dot (CD) powders. Herein, we report a novel and general solvothermal strategy to in-situ embedding CDs in trisodium citrate crystal matrix, and these CDs exhibit tunable emission from green to yellow and a high quantum yield up to 21.6% in solid state, comparable to that in solution. This intriguing fluorescence phenomenon may be caused by the space confinement from trisodium citrate crystal matrix, thus enabling CDs to effectively suppress the aggregation-induced luminescence quenching. The CD powders have been employed for fabricating white light-emitting devices on blue chips with adjustable color temperature. Moreover, solid-state lighting systems like flexible fluorescent films and plates have been demonstrated by using the CD powders as the luminescent medium. This work provides a facile way to achieve tunable solid-state fluorescence CD powders, which have promising applications in CDs-based luminescence devices. [ABSTRACT FROM AUTHOR]