Advanced Optical Materials最新文献

Near-infrared (NIR) photodetection and imaging have sparked significant interests across a wide range of applications. While silicon photodiodes are commonly employed, the small light absorption coefficients of Si in NIR severely limit the performance, especially in the case of thin active Si layers. Although various light harvesting techniques are proposed to increase light absorption of Si, pixel-level strategy for enhanced NIR imaging is still challenging in CMOS image sensors (CISs) with a pixel size in only a micron scale. In this paper, plasmonic metasurfaces are intimately integrated on top of 2.3 µm thick Si active regions of the pixels of a backside illumination (BI)-CIS for NIR imaging for the first time. 200% improved photoresponsivity is obtained in experiments in such a planar Si layer rather than patterning the Si layer with potential damage to the active region. Numerical simulation results reveal highly enhanced light intensity in the thin active Si layer due to the presence of plasmonic metasurfaces. Significantly improved imaging brightness and signal-to-noise ratio of NIR imaging are demonstrated under both laser and LED illumination. This CMOS-compatible technique is expected to hold promising potentials in applications including machine vision, iris certification, light detection and ranging (LiDAR), and optical communication in data centers.

High-performance 0D–2D hybrid photodetectors integrated with a crosslinker for direct pattering of quantum dots on the large-scale synthesized MoS₂ layer are reported. In the patterned hybrid structure, QD layers are patterned with a resolution of up to 2 µm, ensuring high precision. Enhanced charge transfer from QDs to 2D materials is confirmed using PL quenching, TR-PL, and UPS analysis. As a result, the QD/2D hybrid photodetectors with crosslinker-assisted direct patterning demonstrated a remarkable photoresponsivity of ≈10⁵ A W⁻¹ and a specific detectivity of over 10¹¹ Jones, attributed to the difference in built-in potential. The crosslinker patterning of QDs opens up potential applications for the photodetectors in highly integrated image sensors and can be further extended to high-resolution display industries, eliminating unnecessary fabrication processes.

Nonlayered palladium sulfide (PdS) is of interest due to its rich physical properties and promising applications in optoelectronic devices. However, the growth of thin nonlayered PdS remains challenging because of its intrinsic 3D lattice structure. Here, the first demonstration of the direct synthesis of thin rectangular PdS ribbons/flakes on SiO₂/Si substrates by a facile chemical vapor deposition (CVD) approach is presented. The atomic structure and high crystalline quality of CVD-derived PdS crystals are shown by scanning transmission electron microscopy. The nonlinear saturable absorption and absorption enhancement are revealed by using ultrafast optical pump-probe spectroscopy, and the photocarrier dynamics present the hot phonon bottleneck and Auger recombination effects. Additionally, the Raman vibration modes display the polarization-dependent properties verified by angle-resolved polarized Raman spectroscopy. Importantly, the photodetector based on PdS ribbon demonstrates a decent photoresponsivity of ≈7.7 × 10³ A W⁻¹. These results provide an effective way to form thin nonlayered PdS with potential applications in the field of photodetection.

Achieving a wide-range color-tunable and dynamically long-afterglow emission in a single-doped system remains a challenge. In this study, a unique host-guest doped material, TPA-PTPQ/TPA, exhibits dual-delay emission at 516 and 605 nm, both with long lifetimes of up to 108 and 145 ms, which derives from thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) mechanisms, respectively. Notably, this host-guest material demonstrates a temperature-dependent dynamically reversible afterglow characteristic, transitioning green, orange, and red with a substantial spectra shift of ≈90 nm under different temperature conditions. This phenomenon is due to the diverse temperature effect on TADF and RTP emissions. These remarkable luminescence properties are successfully applied in security checks and anti-counterfeiting encryption. This study provides valuable insights into the design of dynamically reversible dual-delay-emissive long-afterglow luminescent materials based on a host-guest doping system.

Recently, it is shown (Popov et al, Sci. Rep, 2017, 7, 1603) that chiral nematic liquid crystal films adopt biconvex lens shapes underwater, which may explain the formation of insect eyes, but restrict their practical application. Here it is demonstrated that chiral ferroelectric nematic liquid crystals, where the ferroelectric polarization aligns parallel to the air interface, can spontaneously form biconvex lens arrays in air when suspended in submillimeter-size grids. Using Digital Holographic Microscopy, it is shown that the lens has a paraboloid shape and the curvature radius at the center decreases with increasing chiral dopant concentration, i.e., with decreasing helical pitch. Simultaneous measurements of the imaging properties of the lenses show the focal length depends on the pitch, thus offering tunability. The physical mechanism of formation of the self-assembled ferroelectric nematic microlenses is also discussed.

The development of optoelectronic devices based on III–V semiconductor colloidal quantum dots (CQDs) is highly sought after due to their reduced toxicity. While devices based on conventional CQDs (II–VI semiconductors, halide perovskites) have achieved impressive technological leaps since their discovery, the most mature of these compounds contain toxic heavy metal elements (Cd, Hg, or Pb), which are highly undesirable for safe industrial scale applications. The strong covalent bonds of III–V compounds like InP, InAs, or InSb prevent the release of their toxic atoms, making them safer. However, these same bonds create severe material constraints. Namely, their harsher reaction conditions and increased sensitivity to oxidation have kept most of the research focused on material development. Meanwhile, their integration into devices and their coupling to photonic structures lag behind. Here, the integration of InAs/ZnSe core-shell CQDs is advanced. First, the material parameters necessary to design plasmonic gratings coupled to the CQDs are elucidated and those gratings are fabricated. Angle-resolved spectroscopy shows that the plasmon modes successfully couple to the CQD layer's emission leading to a tunable directivity with a 15° linewidth. A 3-fold increase of the PL signal is achieved at normal incidence, thus advancing toward the goal of efficient outcoupling in LEDs.

Intraband carrier relaxation in quantum dots (QDs) has been a subject of extensive spectroscopic investigation for several decades, and have been used to optimize the efficiency of opto-electronic processes. In the past few years, metal halide perovskites-based QDs have been shown to exhibit slow hot-carrier cooling characteristics that are desirable for photo-energy harvesting technologies. While several mechanisms are proposed to rationalize the retardation of the cooling dynamics, including hot-phonon bottleneck and polaronic effects, the role of inter-particle connectivity in these dynamics is largely ignored. Here, an in-depth study of photo-excitation dynamics and carrier cooling on perovskite QD solids with varying degrees of inter-dot coupling is presented. It is observed that inter-particle connectivity has deterministic effects on the many-body interactions that are relevant for carrier cooling. These include carrier–carrier interactions that result in Auger-reheating of the carriers, and lattice characteristics that subsequently affect the phonon-assisted cooling dynamics. This spectroscopic study of ultrafast carrier dynamics in perovskite QD solids establishes inter-dot separation as a critical material design parameter for the optimization of photo-generated carrier temperature, which fundamentally determines the luminescence characteristics and thus the opto-electronic quality of the material.

Multifunctional molecular switches have attracted much attention because of their unique stimulus response behavior and advanced applications. However, precise regulation of the structure for property enrichment is still a great challenge. Herein, the first case of a single-molecule switch BN-S with multiple structurally tunable and full-color fluorescent properties is reported. Interestingly, BN-S exhibits a butterfly-like “metamorphosis” crystal growth process accompanied by full-color fluorescence emission (including white light, CIE = 0.33, 0.33; 456 nm → 610 nm). It is shown that this is related to the reversible B←N bonding and the tunability of the spatial structure of the BN-S. Thus, BN-S exhibits superior multicolor tunability in different states (solid, liquid, and film), and its applications in white-light optical light emitting diodes (OLEDs) and multicolor fluorescent inks also show great promise. This will provide a new strategy for designing and synthesizing the development of multifunctional molecular switching materials and enriching the variety of organoboron luminescent materials.

Recently, giant quantum dots (g-QDs) with a core/interface graded alloy shell/shell structure have shown promise in reducing photoluminescence (PL) intermittency and improving photostability. However, this approach has been mainly demonstrated with red and green emitting g-QDs but the blue-emitting graded alloy QDs has remained less explored. To tackle this challenge, a composition gradient method is employed to create three blue-emitting CdZnS/Cd_xZn_1–xS/ZnS core/interface graded alloy shell/shell (C/A/S) quantum dots (QDs) with different diameters. The sample with the largest diameter (gQD-3) exhibits superior optical characteristics, with a photoluminescence quantum yield (PLQY) of approximately 62% and around 80% ON/radiative events at the single-particle level. Conversely, the smallest diameter (gQD-1) sample shows lower PLQY and only 30% radiative events with longer OFF/nonradiative events. Probability distribution analysis of PL trajectories, fitted with a truncated power law, reveals a significantly higher carrier de-trapping rate in gQD-3 compared to gQD-1, attributed to its proximity to band edge trap states. Additionally, the largest diameter sample retains remarkable optical performance during 48 h of continuous UV irradiation in colloidal suspension and single-particle levels. These findings show optimized core/shell structures, gradual alloy interfaces, and outer shell coatings can stabilize blue-emitting quantum dots, advancing next-gen optoelectronics.

Halide anion migration in organic–inorganic metal halide perovskites significantly influences the power conversion efficiency (PCE) and hysteresis of perovskite solar cells (PSCs). These materials are sensitive to various external stimuli such as light, heat, and electrical bias, highlighting the need for novel post-manufacturing treatment methods alongside a deeper understanding of their mechanisms. Here, a dark electro (DE) treatment is introduced that applies a negative-positive-negative bias to PSC under dark conditions, which is particularly effective for formamidinium (FA) lead iodide (FAPbI₃) PSCs processed with a methylammonium chloride (MACl) additive. The DE treatment, followed by light soaking, results in an average PCE increase of 2.9 ± 1.8% (from an initial 18.2 ± 2.0% to 21.1 ± 0.8% after treatment) with a notable decrease in deviation. It is discovered that residual chloride anions from MACl play a critical role in the DE treatment. The migration of halide anions under a shaking electric bias is investigated using energy-dispersive X-ray spectroscopy (EDX) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). This study elucidates the distribution and impact of residual chloride anions, providing insights into the mechanisms underlying the DE treatment.