Ultralong room‐temperature phosphorescence (RTP) is highly useful for information encryption, organic electronics, bioelectronics, etc. However, the preparation of related metal‐free materials with multiple colors across the full spectrum remains a major challenge. Herein, a facile method is developed to fabricate boron‐doped carbon dot (B‐CD) composites with full‐color long lifetime RTP continuously tailorable in the range of 466–638 nm simply by pyrolysis of the citric acid and boric acid precursors with various mass ratios at different temperatures. This leads to the formation of luminescent B‐CD centers in a rigid polycrystalline B2O3 matrix, which effectively stabilizes the triplet excited states of B‐CDs. Thus, the composites become phosphorescent over a relatively long period (5–12 s) after the removal of the irradiation source. Meanwhile, the increased particle size and oxidation degree of B‐CDs obtained at larger citric acid feeding or higher pyrolysis temperature continuously shift the phosphorescence from blue to red. Due to the formation of multiple luminescence centers, the RTP can also be finely modulated by the excitation wavelength. The resulting B‐CD composites with highly tunable long lifetime RTP further allow a variety of distinctive applications in multidimensional encryption handily utilizing space, time, and color variations.

S-CQDs were chosen as a light emitting layer by virtue of their structure characteristics, optical properties and film-forming ability to obtain CQD-LEDs.

The synthesis and luminescence origin of multicolour long wavelength CQDs and solid state luminous red-green-blue CQD films for CQD phosphor-based WLEDs with a high CRI and an adjustable CCT.