Triplet Fusion Upconversion Nanocapsules for Volumetric 3D Printing

TL;DR

This paper introduces a novel volumetric 3D printing method using triplet fusion upconversion nanocapsules, enabling low-power, fast, and scalable printing without expensive ultrafast lasers, expanding the accessibility of volumetric manufacturing.

Contribution

The authors develop a scalable nanocapsule-based upconversion system that supports low-power, high-speed volumetric 3D printing, overcoming limitations of traditional two-photon methods.

Findings

Supports volumetric printing at <4 mW power

Enables scatter-free nanocapsule dispersal in organic media

Achieves printing speeds significantly faster than two-photon methods

Abstract

Two-photon photopolymerization delivers prints without support structures and minimizes layering artifacts in a broad range of materials. This volumetric printing approach scans a focused light source throughout the entire volume of a resin vat and takes advantage of the quadratic power dependence of two photon absorption to produce photopolymerization exclusively at the focal point. While this approach has advantages, the widespread adoption of two photon photopolymerization is hindered by the need for expensive ultrafast lasers and extremely slow print speeds. Here we present an analogous quadratic process, triplet-triplet-annihilation-driven 3D printing, that enables volumetric printing at a focal point driven by <4 milliwatt-power continuous wave excitation. To induce photopolymerization deep within a vat, the key advance is the nanoencapsulation of photon upconversion solution within a silica shell decorated with solubilizing polymer ligands. This scalable self-assembly approach allows for scatter-free nanocapsule dispersal in a variety of organic media without leaking the capsule contents. We further introduce an excitonic strategy to systematically control the upconversion threshold to support either monovoxel or parallelized printing schemes, printing at power densities multiple orders of magnitude lower than power densities required for two-photon-based 3D printing. The application of upconversion nanocapsules to volumetric 3D printing provides access to the benefits of volumetric printing without the current cost, power, and speed drawbacks. The materials demonstrated here open opportunities for other triplet fusion upconversion-controlled applications.