The use of upconversion microparticles as a novel internal radiation source for fabrication of composite materials

Abstract

Upconversion (UC) microparticles were used as novel internal radiation sources for composite preparation. These particles emit Ultraviolet-Visible radiation when exposed to Near-infrared waves. This radiation causes uniform and deep polymerization. Two types of UC particles were prepared via a facile hydrothermal method, including NaLuF 4 : Yb 20%, Tm 0.5% and NaLuF 4 : Yb 40%, Tm 0.5%. The effect of three different photoinitiator systems, including titanocene, bisacylphosphine oxide, and camphorquinone, on the cure depth and the degree of conversion (DC) was investigated. Polymerization reaction rate was also studied. Moreover, the effect of weight percentage of UC particles and laser intensity on the cure depth and the DC were evaluated. Rheological behavior of the composites with different percentage of the particles (1, 3, and 5%) and the effect of temperature were studied. The results showed that the overlap of the UC particles emission spectrum with the photoinitiator absorption spectrum and the intensity of the photoinitiator absorption in the emission range of the particles are of the most important factors affecting cure depth, rate and DC. The cure depth with DC up to approximately 80% was 41 mm. Moreover, the DC was almost constant along the sample. POLYM. COMPOS., 00:000-000,

Lanthanide‐Doped Nanoparticles for Near‐Infrared Light Activation of Photopolymerization: Fundamentals, Optimization and Applications

“…also reported that the curing depth could be increased from 0.5 cm to 3 cm (Figure 5c). In addition, the monomer conversion was improved from 25 % to around 75 % (Figure 5d) when the laser power was increased from 1.5 W to 4.5 W [52] . However, it should be notable that the excited levels of activator ions would be saturated and the emission intensity reaches maximum when the laser power exceeds a certain threshold.…”

“…As anticipated, the UC‐40 exhibited stronger upconversion luminescence than UC‐20 due to more absorption of incident NIR photons with higher concentration of sensitizer ions. As a result, the curing depth for UC‐40 is increased by a couple of times than that for UC‐20 (Figure 6a) [52] . Currently, the upconversion quantum yield of nano‐sized UCNPs is generally below 1 %, which is significantly lower than the micro‐sized counterparts.…”

“…(c, d) Effect of laser intensity on cure depth and conversion. Reproduced with permission [52] . Copyright 2018, John Wiley &Sons, Inc. (e) The curing depth varies with the output power.…”

“… (a) Upconversion emission spectra of UC‐20 and UC‐40, and influence of internal light source on cure depth in the presence of different photoinitiators. Reproduced with permission [52] . Copyright 2018, John Wiley &Sons, Inc. (b) Cartoon schematic of the intensity enhancement in the dye‐sensitized UCNP system, conveying the much larger absorption cross‐section of IR806 relative to the UCNP, as well as S 1 →T 1 ISC enhancement by Ln 3+ .…”

“…In addition, photoinitiators should also have high extinction coefficient in the emission wavelength region of UCNPs to ensure adequate absorption of these UCNP emissions. Irgacure 784 (bis(2,6‐difluoro‐3‐(1‐hydropyrrol‐1‐yl)phenyl) titan‐ ocene), which is currently the most widely used commercial photoinitiator in UCNP‐assisted photopolymerization, has the high overlap with the emission spectra of UCNPs, the high molar absorption coefficient (884 L/(mol cm)) and strong initiating ability (Figure 9a) [52–54] . Liu et al.…”