The realization of high‐contrast modulation in optically transparent media is of great significance for emerging mechano‐responsive smart windows. However, no study has provided fundamental strategies for maximizing light scattering during mechanical deformations. Here, a new type of 3D nanocomposite film consisting of an ultrathin (≈60 nm) Al2O3 nanoshell inserted between the elastomers in a periodic 3D nanonetwork is proposed. Regardless of the stretching direction, numerous light‐scattering nanogaps (corresponding to the porosity of up to ≈37.4 vol%) form at the interfaces of Al2O3 and the elastomers under stretching. This results in the gradual modulation of transmission from ≈90% to 16% at visible wavelengths and does not degrade with repeated stretching/releasing over more than 10 000 cycles. The underlying physics is precisely predicted by finite element analysis of the unit cells. As a proof of concept, a mobile‐app‐enabled smart window device for Internet of Things applications is realized using the proposed 3D nanocomposite with successful expansion to the 3 × 3 in. scale.

Graphene quantum dots (GQDs) have attracted great attention as next-generation luminescent nanomaterials due to the advantages of a low-cost process, low toxicity, and unique photoluminescence (PL). However, in the solid-state, the strong π−π stacking interactions between the basal planes of GQDs lead to aggregation-caused PL quenching (ACQ), which impedes practical application to light-emitting devices. Here, surface functionalized GQDs (F-GQDs) by polyhedral oligomeric silsesquioxane (POSS), poly(ethylene glycol) (PEG), and hexadecylamine (HDA) to reduce π−π stacking-induced ACQ is presented. The POSS-, PEG-, and HDA-functionalized GQDs show a significant enhancement in PL intensity compared to bare GQDs by 9.5-, 9.0-, and 5.6-fold in spin-coated film form and by 8.3-, 7.2-, and 3.4-fold in drop-casted film form, respectively. Experimental results and molecular dynamics simulations indicate that steric hindrance of the functionalization agent contributes to reducing the π−π stacking between adjacent GQDs and thereby enabling quenching-resistant PL in the solid-state. Moreover, the GQD-based white light-emitting diodes fabricated by mounting HDA-GQDs on a UV-LED chip exhibits efficient downconversion for white light emission with a high color rendering index of 86.2 and a correlated-color temperature of 5612 K at Commission Internationale de l'Éclairage coordinates of (0.333, 0.359).

Three-dimensional (3D) nanoarchitectures have offered unprecedented material performances in diverse applications like energy storages, catalysts, electronic, mechanical, and photonic devices. These outstanding performances are attributed to unusual material properties at the nanoscale, enormous surface areas, a geometrical uniqueness, and comparable feature sizes with optical wavelengths. For the practical use of the unusual nanoscale properties, there have been developments for macroscale fabrications of the 3D nanoarchitectures with process areas over centimeter scales. Among the many fabrication methods for 3D structures at the nanoscale, proximity-field nanopatterning (PnP) is one of the promising techniques that generates 3D optical holographic images and transforms them into material structures through a lithographic process. Using conformal and transparent phase masks as a key factor, the PnP process has advantages in terms of stability, uniformity, and reproducibility for 3D nanostructures with periods from 300 nm to several micrometers. Other merits of realizing precise 3D features with sub-100 nm and rapid processes are attributed to the interference of coherent light diffracted by phase masks. In this review, to report the overall progress of PnP from 2003, we present a comprehensive understanding of PnP, including its brief history, the fundamental principles, symmetry control of 3D nanoarchitectures, material issues for the phase masks, and the process area expansion to the wafer-scale for the target applications. Finally, technical challenges and prospects are discussed for further development and practical applications of the PnP technique.

One of the well‐known strategies for achieving high‐performance light‐activated gas sensors is to design a nanostructure for effective surface responses with its geometric advances. However, no study has gone beyond the benefits of the large surface area and provided fundamental strategies to offer a rational structure for increasing their optical and chemical performances. Here, a new class of UV‐activated sensing nanoarchitecture made of highly periodic 3D TiO2, which facilitates 55 times enhanced light absorption by confining the incident light in the nanostructure, is prepared as an active gas channel. The key parameters, such as the total 3D TiO2 film and thin‐shell thicknesses, are precisely optimized by finite element analysis. Collectively, this fundamental design leads to ultrahigh chemoresistive response to NO2 with a theoretical detection limit of ≈200 ppt. The demonstration of high responses with visible light illumination proposes a future perspective for light‐activated gas sensors based on semiconducting oxides.

The practical use of photonic crystals with structural colors requires technology capable of rapidly producing large‐area, three‐dimensional (3D) periodic nanostructures. Until now, the fabrication of 3D photonic crystals has relied mainly on additive manufacturing and colloidal self‐assembly. These technologies have provided a useful academic platform based on precisely controlled 3D periodicity but have not evolved into mass production technology. Here, optical lithography for the rapid fabrication of large‐area 3D photonic crystals with structural colors is introduced. The key strategy is to incorporate two orthogonal line gratings (periodicity: 300 nm) made of an elastomer to create a conformal multilevel phase mask. When the mask is irradiated with a 355 nm laser, the five beam interference is established in the proximity region. The interlayer thickness between the two orthogonal line gratings controls the phase difference, which is closely related to the symmetry of the resulting 3D interference pattern. The interlayer thickness is designed to produce a woodpile structure with a planar periodicity of 300 nm and a vertical periodicity of 716 nm. The pattern area of the woodpile photonic crystal is expanded to 1 in2. Red, green, and blue colors are experimentally realized by controlling the vertical shrinkage of the photoresist.