1550 nm Three-Photon Direct Laser Writing Based on a Quantum Photoinitiator

Direct laser writing (DLW) technology based on long wavelengths has the advantages of deep penetration, a wide range of processing materials, small scattering, and high resolution. However, owing to the small absorption cross-section of conventional organic photoinitiators, the realization of 1550 nm DLW is difficult. Nano quantum dot (QD) (QD)-based photoinitiators have many outstanding advantages, making the 1550 nm DLW possible. However, the reported 780 or 840 nm two-photon DLW polymerization effect using QDs photoinitiators with relatively low doping concentrations is not ideal. To address these issues, in this study, surface-modified CdSe QDs with a high doping concentration of 200 mg/mL are employed as a photoinitiator and a functional luminescent nanomaterial, which could generate COO* free radicals and initiate the polymerization of the resin monomer, thereby realizing the 1550 nm three-photon DLW. Based on this mechanism, various luminescent QD–polymer micro-/nanostructures are successfully fabricated. Moreover, multicolor and white QD–polymer dot arrays, flexible displays, and 220 nm dot arrays with a high resolution of up to 56,444 ppi have been realized. We also achieved a superfine feature size of 95 nm. We further demonstrate the feasibility of the 1550 nm three-photon DLW for fabricating QD–polymer color conversion layers for full-color microlight-emitting diode (micro-LED) displays and metasurfaces for optical holography. Therefore, this study provides a method to implement DLW technology based on a longer laser wavelength of 1350–2000 nm, which facilitates the high feasibility of QD–polymer micro-/nanostructures for diverse applications, including micro-LED displays, augmented reality/virtual reality displays, three-dimensional displays, and lighting and optical holography.