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

Abstract

Phosphorescent inks based on carbon nanodots (CNDs) offer an environmentally friendly and low-cost alternative for persistent visibility and time-delayed information retrieval. However, current matrix-dependent phosphorescent CNDs suffer from poor processability and limited substrate compatibility, hindering their application in scalable, high-resolution invisible printing. Here, we report water-soluble phosphorescent CND inks that enable high-resolution, environmentally stable, and invisible printing. The triplet excitons in CNDs are stabilized by spatial confinement during printing, resulting in bright and long-lived phosphorescence. The phosphorescent CND inks enable invisible yet high-fidelity printing of complex textual patterns with micrometer resolution (2480 × 3508 dpi, ∼100 μm feature size), supporting font sizes down to 5 pt and line widths as thin as 0.05 pt across five types of paper substrates. The printed patterns exhibit over 98.7 % accuracy across approximately 8.7 million pixels, demonstrating excellent fidelity. Based on these excellent invisible printing properties, a 200-page wordless book using phosphorescent CND inks was demonstrated. This work presents a scalable, low-cost, and high-resolution platform for phosphorescent ink printing, marking a significant advance in invisible printing technology.