Advanced Optical Materials最新文献

Persistent Luminescent Materials

Frequency-domain analysis is used to study afterglow, enabling the direct measurement of charge trapping rates in persistent luminescent materials. This method offers new insights into trapping efficiency and performance, surpassing traditional time-domain techniques and promoting rational material optimization. More details can be found in the Research Article by Manuel Romero, Gabriel Lozano, and co-workers (DOI: 10.1002/adom.202501847).

Circularly Polarized Light

Based on the chiral structure of hydroxypropyl cellulose, chiral photonic films and multi-wavelength circularly polarized fluorescence films are prepared, resulting in functional multi-color arrays for advanced photonic applications. This study promoting the application of cellulose materials in structural color coatings, chiroptical devices, and advanced displays. More details can be found in the Research Article by Mingcong Xu, Shouxin Liu, Wei Li and co-workers (DOI: 10.1002/adom.202501959).

Infrared (IR) up-conversion from the 3 to 0.8 µm wavelength range is demonstrated using resonantly enhanced second-order sum-frequency generation (SFG) in hybrid metasurfaces comprising of thick gallium selenide (GaSe) integrated amorphous silicon metasurfaces. Silicon-on-quartz metasurface comprising asymmetric meta-atoms is designed to support collective electric-dipole (ED)-like and quasi-bound-state-in-the-continuum (quasi-BIC) resonances at 3.06 and 3.34 µm wavelength, respectively. The optimal thickness of multilayer GaSe is determined to be ≈70 nm in order to maximize the far-field radiated SFG. The choice of a thick optimized GaSe layer in this work is motivated by its lower refractive index when compared to the silicon structures, resulting in minimal change to the optical resonances and electric field profiles while increasing the nonlinear interaction volume and far-field radiated SFG. Resonant SFG up-conversion from the hybrid structures is demonstrated with resonant enhancement of 59- and 35-times from the ED-like and quasi-BIC resonances. To the best of the knowledge, this is the first report of such resonant infrared up-conversion from the mid-IR to shorter near-IR using hybrid metasurfaces. This work paves the path for realizing compact frequency conversion devices operating across widely separated wavelengths using emerging resonant photonic platforms for potential applications in infrared sensing and imaging.

Terahertz (THz) radiation is a powerful probe of low-energy excitations in all phases of matter. However, it remains a challenge to find materials that efficiently generate THz radiation in a broad range of frequencies following optical excitation. Here, we investigate a pyroelectric material, ZnSnN₂, and find that its above-band-gap excitation results in the efficient formation of an ultrafast photocurrent generating THz radiation. The resulting THz electric field spans a frequency range from below 1 THz to above 30 THz. The results suggest that the photocurrent is primarily driven by an ultrafast pyroelectric effect where the photo-excited carriers screen the spontaneous electric polarization of ZnSnN₂. Strong structural disorder reduces the photocarrier lifetime significantly and, thus, enables broadband operation. ZnSnN₂ shows a similar THz-emitter performance as the best spintronic THz emitters regarding bandwidth and amplitude. The study unveils the large potential of pyroelectric materials as efficient and broadband THz emitters with built-in bias fields.

Flexible near-infrared photodetectors are particularly promising for applications in wearable technology, non-invasive biosensing and bioimaging, and environmental monitoring. Germanium (Ge) is widely used as an active material for high-performance near-infrared photodetectors, since its energy bandgap (0.67 eV) excellently matches the near-infrared band. However, the fabrication of Ge-based flexible near-infrared photodetectors is strongly challenged by the difficulties in preparing flexible Ge membranes. Although various attempts have been developed, they suffer from one or more disadvantages, such as high cost, inconvenient transfer printing, and/or difficulty in processing. Herein, photoresist-mediated transfer printing is proposed for preparation of Ge membranes, which are obtained by the wet thinning of a bulk wafer with vertical PN junction structures. The introduced photoresist medium layer could protect the doped surface of Ge against corrosion during the thinning process, and facilitate the complete transfer of the thinned Ge membranes onto flexible substrates. With the prepared Ge membranes, flexible near-infrared photodiodes with good and robust optoelectronic performances against mechanical bending, including various bending radii and bending cycles, are successfully demonstrated. The proposed technique can be adapted for fabricating a broad range of flexible Ge-based electronics.

The rapid advancement of near-infrared (NIR) laser applications has created an urgent demand for optical filters that simultaneously achieve decorative coloration, mechanical robustness, and high transmission at laser wavelengths. In this work, a 7-layer Si₃N₄/Si alternating multilayer structure is fabricated on colored glass using magnetron sputtering technology. The optimized photonic structure exhibits specular RGB colors while maintaining exceptional transmittance (>90%) at the NIR laser wavelengths of 930–940 nm, with the total thickness in the order of 500 nm. This unique optical performance originates from precisely engineered admittance matching within the Si₃N₄/Si multilayer architecture. Moreover, the Si₃N₄-dominated framework demonstrates outstanding mechanical durability and scratch resistance owing to its inherent high hardness. By integrating color performance, NIR transmission, and mechanical protection into a single device, the proposed design not only addresses key functional requirements but also provides an advanced solution for applications in laser display, NIR sensing/monitoring, and optical anti-counterfeiting.

Upconversion nanoparticles (UCNPs) exhibit exceptional nonlinear optical properties that offer powerful capabilities for super-resolution imaging. In this study, we exploit the dynamic nonlinear characteristics of lanthanide-doped UCNPs to propose a multi-order dynamic nonlinear stepwise optical saturation (DN-SOS) image scanning microscopy (ISM), effectively overcoming the diffraction limit inherent in conventional ISM techniques. To elucidate the nonlinear fluorescence behavior of UCNPs under varying excitation conditions, a complete rate-equation model is established, and Taylor expansion of the fluorescence signal reveals that higher-order terms encode high spatial frequency information for resolution enhancement. By dynamically modulating excitation power during image acquisition, nonlinear fluorescence response images are captured, and a multi-image weighted finite difference method is applied to suppress lower-order components in the Taylor expansion, thereby extracting high spatial frequency details. Although unlimited resolution enhancement is theoretically attainable, practical performance is constrained by the signal-to-noise ratio (SNR). Utilizing a custom-built confocal setup with 980 nm excitation laser and 800 nm detection, we demonstrate fourth-order DN-SOS imaging with a lateral resolution of ≈130 nm, around an eighth of the excitation wavelength. This corresponds to a threefold improvement beyond the diffraction limit. The method offers a simple solution for super-resolution imaging in point-scanning systems without complex synchronization schemes.

Electron-hole (e-h) pairs are key intermediates in the recombination processes of organic electroluminescence (OEL) devices, and understanding their behavior during operation is critical for optimizing their performance. Here, electroluminescence (EL)-detected magnetic resonance (ELDMR) techniques are utilized to probe e-h pairs in light-emitting electrochemical cells (LECs) under operando conditions, aiming to elucidate their characteristic device operation behaviors. The results reveal that the ELDMR signal originates from electron spin resonance at e-h pairs, and that the ELDMR technique effectively probes the influence of internal electric fields in LECs via the field-sensitive spin properties of these pairs. The ELDMR response of LECs shows hysteresis during voltage sweeps. The analysis reveals that the internal electric field decreases during the reverse sweep. Importantly, this reduction results in a significant enhancement of external EL efficiency and a stronger magneto-EL effect, highlighting the influence of the internal electric field on recombination processes. These findings demonstrate the value of ELDMR approaches and suggest that controlling the electric field environment via e-h pairs is essential for improving the performance of OEL devices.

In this work, tunable vanadium dioxide (VO₂) metafilms on different substrate materials fabricated via low-oxygen furnace oxidation are demonstrated for self-adaptive daytime solar heating and nighttime radiative cooling. Because of its thermally-driven insulator-to-metal phase transition behavior, the VO₂ metafilms work as a spectrally-selective solar absorber with a high solar absorptance of 0.86 and a low infrared emissivity of ≈0.2 at daytime, while they behave as a selective cooler at nighttime to dissipate heat effectively through the atmospheric transparency window with a high emissivity of ≈0.76 to cold outer space. From the outdoor vacuum tests, a significant temperature rise up to 169 K upon solar heating and a temperature drop of 17 K at night are experimentally observed from these tunable VO₂ metafilms. With effective atmospheric temperature fitted in situ, the accurate heat transfer model shows excellent agreement with the stagnation temperature measurement, indicating a high heating power of ≈400 W m⁻² at 80 °C sample temperature in the middle of the day, and a cooling power of ≈60 W m⁻² at 30 °C in equilibrium with the ambient at night. This work would facilitate the development of self-adaptive coatings with cost-effective and scalable fabrication approaches for all-day energy harvesting.

Broadband near-infrared (NIR) luminescent materials are crucial in near-infrared smart devices and optical communications, but conventional cadmium-based NIR materials have toxic risks. Biocompatible silicon nanomaterials with tunable emission wavelengths offer a promising alternative. Here, silicon nanocrystal composites (Si NCs/SiO₂) with broadband NIR emission spanning from 600 to 1000 nm are synthesized through precise control of the microstructure of silicon polymer precursors. Si NCs/SiO₂ exhibit a unique nano-embedded microstructure, and their NIR photoluminescence quantum yield reaches up to 28.1%. Moderately reducing the precursor water content effectively enhances Si NCs growth quality, photoluminescence, and stability. Comprehensive characterization elucidates the critical role of the synergistic effect between quantum confinement and radiative recombination at the suboxide interface in the NIR emission. Furthermore, Si NCs/SiO₂ retains over 90% of its luminescent intensity at an elevated temperature of 328 K, demonstrating excellent thermal stability and resistance to thermal quenching. Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) fabricated using Si NCs/SiO₂ exhibit stable emission under high driving currents and demonstrate superior performance in nondestructive evaluation, biological imaging, information encryption, and night vision imaging. This work establishes a design framework for environmentally friendly near-infrared luminescent materials and underscores the potential of silicon-based nanomaterials for practical applications.