  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.
