Hydrothermal synthesis of NaYF4:Yb3+,Tm3+ upconversion microparticles and their effects on polymerization for stereolithography

Abstract

Using near-infrared (NIR) laser to induce polymerization of photosensitive resin containing upconversion microparticles can effectively solve the problem of limited curing depth in traditional stereolithography (SLA). But for an accurate printing structure, in addition to the curing depth, the cross-section diameter is also an important factor. In this study, NaYF 4 :Yb 3+ ,Tm 3+ upconversion microparticles with different Tm 3+ concentrations (0.2 mol%, 1.2 mol% and 1.7 mol%) were prepared at different hydrothermal temperatures (150 °C and 200 °C), respectively. The synthesized microparticles were added to the photosensitive resin with different concentrations (0.0625 wt%, 0.125 wt%, 0.25 wt%, 0.5 wt% and 1.0 wt%) and irradiated with a 975 nm semiconductor laser to observe the curing phenomenon. The effects of the fluorescence properties and concentration of upconversion microparticles on the curing depth and cross-section diameter were investigated. Results showed that the curing depth could reach 41 mm and the curing cross-section diameter could be as small as 0.22 mm. And it was easy to control the curing depth and cross-section diameter by changing the Tm 3+ concentration, hydrothermal temperature and upconversion microparticles' concentration. Therefore, upconversion microparticles and their concentration can be reasonably selected according to the different requirements of the printed structure. Finally, 3D objects with different heights and finenesses were printed. • Compared with the traditional ultraviolet light source, the near-infrared laser has a deeper penetration depth in the resin. • Use upconversion material as internal light source. • Nvestigated the effect of upconversion materials on the cross-section diameter of the cured sample.