Preparation of Quantum Dot-Embedded Photonic Crystal Hydrogel and Its Application as Fluorescence Sensor for the Detection of Nitrite

The development of fluorescence sensing platforms with excellent photoluminescence capabilities is of great importance for their further application. In this work, a photonic crystal structure was successfully applied to enhance the luminescence performance of fluorescent hydrogel, and the application of the obtained hydrogel as a fluorescence sensor was explored. A polystyrene photonic crystal template was constructed via vertical deposition self-assembly; then, the precursor solution containing polyethylenimine-capped CdS quantum dots (PEI-CdS QDs) and monomers filled in the gap of the template. After the polymerization process, the desired hydrogel was obtained. PEI-CdS QDs endowed the hydrogel with its fluorescence property, while interestingly, the photonic crystal structure showed a significant enhancement effect on the fluorescence-emission capability. The mechanism of this phenomenon was revealed. Moreover, this hydrogel could be used as a reusable fluorescence sensor for the detection of nitrite in water with good selectivity. The limit of detection was determined to be 0.25 μmol/L, which is much lower than the maximum limit for nitrite in drinking water.

Rational Design and Simulation of Two-Dimensional Perovskite Photonic Crystal Absorption Layers Enabling Improved Light Absorption Efficiency for Solar Cells

A two-dimensional perovskite photonic crystal structure of Methylamine lead iodide (CH3NH3PbI3, MAPbI3) is rationally designed as the absorption layer for solar cells. The photonic crystal (PC) structure possesses the distinct “slow light” and band gap effect, leading to the increased absorption efficiency of the absorption layer, and thus the increased photoelectric conversion efficiency of the battery. Simulation results indicate that the best absorption efficiency can be achieved when the scattering element of indium arsenide (InAs) cylinder is arranged in the absorption layer in the form of tetragonal lattice with the height of 0.6 μm, the diameter of 0.24 μm, and the lattice constant of 0.4 μm. In the wide wavelength range of 400–1200 nm, the absorption efficiency can be reached up to 82.5%, which is 70.1% higher than that of the absorption layer without the photonic crystal structure. In addition, the absorption layer with photonic crystal structure has good adaptability to the incident light angle, presenting the stable absorption efficiency of 80% in the wide incident range of 0–80°. The results demonstrate that the absorption layer with photonic crystal structure can realize the wide spectrum, wide angle, and high absorption of incident light, resulting in the increased utilization efficiency of solar energy.

Flexible Structural Color Films Based on Electro-Hydrodynamic Inkjet Printing

Structural coloration based on nanostructures is one of the alternatives that can prevent environmental pollution compared to the use of chemically synthesized materials. This technique has attracted considerable attention for various applications, including displays and sensors. In this study, a photonic crystal structure based on spherical silica was formed to provide structural color using an electro-hydrodynamic (EHD) equipment, a printed electronic system attracting considerable interest. The EHD inkjet printing equipment could print micro- and nanostructures using the voltage applied between the nozzle and substrate. Silica-based ink samples were prepared for use in the EHD equipment. Appropriate printing parameters for the EHD inkjet printing were set using the prepared sample. Spherical silica was printed on a polyimide (PI) film layer. The spherical silica nanoparticles discharged during the EHD inkjet printing were not deformed by the EHD process. A photonic crystal structure was formed on a polydimethylsiloxane (PDMS) layer by EHD printing by covering the PDMS layer on the PI film. The spherical-silica-based photonic crystal structure formed on the PDMS layer with elasticity and flexibility exhibited a color change with bending loads.