Doped Carbon Dots Enable Highly Efficient Multiple‐Color Room Temperature Phosphorescence

Colloidal carbon dots (C‐dots) are considered as promising heavy‐metal‐free materials to achieve room‐temperature phosphorescence (RTP) properties for promising applications, such as photoelectronic devices, information encryption, and bio‐imaging. However, most of the current obtained RTP C‐dots have a short lifetime with a relatively low quantum yield (QY). In this work, the C‐dots large‐scale synthesized via a vacuum heating approach have multiple RTP emissions (blue, green, and yellow), a long RTP lifetime of as high as 1.92 s, and a high QY of 34.4% by selecting different types of precursors, which is superior to most of reported RTP C‐dots. The multiple atoms doping and strong bonding between neighbored C‐dots promoted by vacuum heating contributes to the excellent RTP properties. As a proof‐of‐concept, the as‐obtained RTP C‐dots are used as optical ink for flexible security codes, exhibiting a bright shape with a lifetime of 1.37 s. This work offers an efficient approach for producing large‐scale high‐quality RTP C‐dots, which can be applied to anti‐counterfeiting and information encryption systems. A vacuum‐heating approach is demonstrated for large‐scale production of over ten grams per batch. The as‐prepared carbon dots (C‐dots) exhibit multiple room‐temperature phosphorescence (RTP) emissions (blue, green, and yellow) and a long RTP lifetime of 1.92 s with a maximum quantum yield of 34.4%. As a proof‐of‐concept, the as‐synthesized RTP C‐dots are used as ink for flexible security codes, exhibiting a bright shape with a lifetime of 1.37 s.