Abstract
Utilizing lanthanide upconversion nanoparticles to convert near-infrared to visible light presents a potential way for fabricating the next generation of low-cost near-infrared imaging sensors. Integrating microlens arrays with upconversion nanoparticles has been shown to be a promising approach for improving the efficiency of upconversion nanoparticles. However, approaches suitable for prototyping and producing microlens arrays to explore optimal device designs are lacking. In this work, we report an approach to fabricating flexible near-infrared-to-visible upconversion devices incorporating upconversion nanoparticles and microlens arrays, which enables easy adjustment of device structures and lens geometry. This is achieved by fabricating flexible films containing upconversion nanoparticles using molding in combination with femtosecond laser 3D printing of lenses, facilitating rapid prototyping for different application scenarios. By adding the microlens array, the intensities of the green (525 and 540 nm) and red (654 nm) upconversion emission bands were enhanced by a factor of 3 and 10, respectively, potentially leading to much reduced detectable near-infrared light intensity.