Phosphorescent carbon nanodot inks for scalable and high-resolution invisible printing

Luminescent inks are becoming key materials in various technologies and practical applications, with a wide range of application scenarios. However, the emission process of fluorescence essentially relies on short-lived singlet excitons, and this transient characteristic limits its functionality in scenarios requiring persistent visibility and delayed information retrieval. In contrast, phosphorescent inks utilize long-lived triplet excitons to maintain emission even after excitation ceases, offering unique advantages in multi-level security and high-contrast sensing. Carbon nanodots (CNDs), as a new class of zero-dimensional luminescent materials, have attracted extensive attention in fields such as biosensing.

This work reports a water-soluble phosphorescent carbon nanodots (CNDs) ink that can be used for high-resolution invisible printing. Through the spatial confinement effect during printing, the triplet excitons of CNDs can be stabilized, resulting in bright and long-lived phosphorescence. This ink can achieve high-fidelity invisible printing of complex text patterns with a resolution of micrometer level (2480×3508 dpi, approximately 100 μm feature size), and can accurately reproduce text with a minimum font size of 5 pt and a fine line width of 0.05 pt on five types of paper substrates, with an accuracy of over 98.7% in an image of 870,000 pixels. The research team also used its properties to create a 200-page phosphorescent CNDs blank book, providing a new way for the scalable, low-cost, and high-resolution platform of new phosphorescent ink printing. The work entitled “Phosphorescent carbon nanodot inks for scalable and high-resolution invisible printing” was published on Acta Physico-Chimica Sinica (published on September 29, 2025).