High-resolution 3D photopolymerization assisted by upconversion nanoparticles for rapid prototyping applications

Vasilina V. Rocheva,Evgeny V. Khaydukov,Vladimir A. Semchishen,Alla N. Generalova,Anna E. Guller,Anastasia V. Koroleva,Kirill V. Khaydukov,Andrey V. Nechaev,Boris N. Chichkov,Alexander G. Savelyev

doi:10.1038/s41598-018-21793-0

Abstract

Three-dimensional (3D) rapid prototyping technology based on near-infrared light-induced polymerization of photocurable compositions containing upconversion nanomaterials has been explored. For this aim, the rationally-designed core/shell upconversion nanoparticles NaYF4:Yb3+,Tm3+/NaYF4, with the distinct ultraviolet-emitting lines and unprecedentedly high near-infrared to ultraviolet conversion efficiency of {eta }_{{bf{UC}}}^{({bf{UV}})}=2{boldsymbol{ % }} have been used. The upconverted ultraviolet photons were capable to efficiently activate photoinitiators contained in light-sensitive resins under moderate intensities of NIR excitation below 10 W cm−2 and induce generation of radicals and photopolymerization in situ. Near infrared-activated polymerization process, both at the millimeter and sub-micron scales, was investigated. Polymeric macro- and microstructures were fabricated by means of near infrared laser scanning photolithography in the volume of liquid photocurable compositions with focused laser light at 975 nm wavelength. Examination of the polymerization process in the vicinity of the nanoparticles shows strong differences in the rate of polymer shell growth on flat and edge nanoparticle sides. This phenomenon mainly defines the resolution of the demonstrated near infrared - ultraviolet 3D printing technology at the micrometer scale level.

Highlights

Photopolymerization processes such as direct laser writing, three-dimensional (3D) micromachining, holography, micro- and optoelectronics, optical element formations, data recording and storage, etc. are widely used in various fields of science, industry and technology[1]
We investigate the feasibility of NIR-induced polymerization of photocurable composition (PCC) containing UV-emitting upconversion nanomaterials under conditions of direct writing by semiconductor laser for the 3D rapid prototyping applications
The core/shell β-NaYF4:Yb3+,Tm3+/NaYF4 upconversion nanoparticles (UCNPs) were synthesized in order to serve as an internal NIR-triggered UV source for photopolymerization at a considerable depth

Summary

Introduction

Photopolymerization processes such as direct laser writing, three-dimensional (3D) micromachining, holography, micro- and optoelectronics, optical element formations, data recording and storage, etc. are widely used in various fields of science, industry and technology[1]. The single-photon polymerization is usually activated by irradiation with ultraviolet (UV) or short-wavelength visible light, but without the repetition steps of adding of the subsequent polymer layers, it is mainly limited to the fabrication of two-dimensional (2D) structures. This shortage stems from the following time and spatial restrictions. The upconversion nanoparticles (UCNPs) composed by NaYF4 ceramic host co-doped with Yb3+ as a sensitizer, and Er3+ or Tm3+ as activator, are considered as one of the most efficient anti-Stokes photoluminescent materials[17] These nanoparticles demonstrate upconversion emission with narrow lines in UV and visible spectral ranges under continuous-wave (CW) excitation at 970–980 nm. These nanoparticles combine a large anti-Stokes shift of several hundred nanometers, non-photoblinking nature, and superior photostability

Methods

Results

Conclusion