High bandwidth semipolar (20-21) micro-LED-based white light-emitting diodes utilizing perovskite quantum dots and organic emitters in color-conversion layers for visible light communication and solid-state lighting applications.

We demonstrate semipolar (20-21) micro-LED-based high-bandwidth WLEDs utilizing perovskite QDs and organic emitters in color-conversion films. The WLEDs exhibit a bandwidth in excess of 1 GHz and a CCT of 6141 K, making these devices suitable for visible light communication and lighting applications.

Strongly Improving the Sensitivity of Phosphorescence-Based Optical Oxygen Sensors by Exploiting Nano-Porous Substrates.

Sensitivity is one of the crucial factors in determining the quality of a fluorescence/phosphorescence-based gas sensor, and is estimated from the measurement of responses (I0/I, where I0 and I refer to the measured optical intensity of a sensor in absence and presence of analyte molecules) at various concentrations of analytes. In this work, we demonstrate phosphorescence-based optical oxygen sensors fabricated on highly porous anodic aluminum oxide (AAO) membranes showing dramatically high response. These sensors exploit the enormous surface area of the AAO to facilitate the effective interaction between the sensing molecules and the analytes. We spin-coat an AAO membrane (200 nm pore diameter) with a platinum-based oxygen sensing porphyrin dye, platinum(II) meso-tetrakis (pentafluorophenyl) porphyrin (PtTFPP), to fabricate a sensor exhibiting I0/I ~400 at 100% oxygen atmosphere. To address the generality of the AAO membrane, we fabricate a separate sensor with another porphyrin dye, platinum octaethylporphyrin (PtOEP), which exhibits an even higher I0/I of ~500. Both of these sensors offer the highest responses as an optical oxygen sensor hitherto reported. SEM and EDS analysis are performed to realize the effect of the increased surface area of the AAO membrane on the enhanced sensitivity.

Ingenious Fabrication of Ag-Filled Porous Anodic Alumina Films as Powerful SERS Substrates for Efficient Detection of Biological and Organic Molecules.

Surface-enhanced Raman scattering (SERS) has been widely used to effectively detect various biological and organic molecules. This detection method needs analytes adsorbed onto a specific metal nanostructure, e.g., Ag-nanoparticles. A substrate containing such a structure (called SERS substrate) is user-friendly for people implementing the adsorption and subsequent SERS detection. Here, we report on powerful SERS substrates based on efficient fabrication of Ag-filled anodic aluminum oxide (AAO) films. The films contain many nanopores with small as-grown inter-pore gap of 15 nm. The substrates are created by electrochemically depositing silver into nanopores without an additional pore widening process, which is usually needed for conventional two-step AAO fabrication. The created substrates contain well-separated Ag-nanoparticles with quite a small inter-particle gap and a high number density (2.5 × 1010 cm-2). We use one-step anodization together with omitting additional pore widening to improve the throughput of substrate fabrication. Such substrates provide a low concentration detection limit of 10-11 M and high SERS enhancement factor of 1 × 106 for rhodamine 6G (R6G). The effective detection of biological and organic molecules by the substrate is demonstrated with analytes of adenine, glucose, R6G, eosin Y, and methylene blue. These results allow us to take one step further toward the successful commercialization of AAO-based SERS substrates.

Recent Advances in Colloidal Quantum Dots or Perovskite Quantum Dots as a Luminescent Downshifting Layer Embedded on Solar Cells.

The solar cell has a poor spectral response in the UV region, which affects its power conversion efficiency (PCE). The utilization of a luminescent downshifting (LDS) layer has been suggested to improve the spectral response of the photovoltaics in the short wavelength region through photoluminescence (PL) conversion and antireflection effects, which then enhance the PCE of the solar cell. Recently, colloidal quantum dots (CQDs) or perovskite quantum dots (PQDs) have been gaining prime importance as an LDS material due to their eminent optical characteristics, such as their wide absorption band, adjustable visible emission, short PL lifetime, and near-unity quantum yields. However, the instability of QDs that occurs under certain air, heat, and moisture conditions limits its commercialization. Thus, in this review, we will focus on the physical and optical characteristics of QDs. Further, we will discuss different synthesis approaches and the stability issues of QDs. Different approaches to improve the stability of QDs will be discussed in detail alongside the recent breakthroughs in QD-based solar cells for various applications and their current challenges. We expect that this review will provide an effective gateway for researchers to fabricate LDS-layer-based solar cells.

Resolving Cross-Sensitivity Effect in Fluorescence Quenching for Simultaneously Sensing Oxygen and Ammonia Concentrations by an Optical Dual Gas Sensor.

Simultaneous sensing of multiple gases by a single fluorescent-based gas sensor is of utmost importance for practical applications. Such sensing is strongly hindered by cross-sensitivity effects. In this study, we propose a novel analysis method to ameliorate such hindrance. The trial sensor used here was fabricated by coating platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and eosin-Y dye molecules on both sides of a filter paper for sensing O2 and NH3 gases simultaneously. The fluorescent peak intensities of the dyes can be quenched by the analytes and this phenomenon is used to identify the gas concentrations. Ideally, each dye is only sensitive to one gas species. However, the fluorescent peak related to O2 sensing is also quenched by NH3 and vice versa. Such cross-sensitivity strongly hinders gas concentration detection. Therefore, we have studied this cross-sensitivity effect systematically and thus proposed a new analysis method for accurate estimation of gas concentration. Comparing with a traditional method (neglecting cross-sensitivity), this analysis improves O2-detection error from -11.4% ± 34.3% to 2.0% ± 10.2% in a mixed background of NH3 and N2.

Recent Advances in Two-Dimensional Quantum Dots and Their Applications.

Two-dimensional quantum dots have received a lot of attention in recent years due to their fascinating properties and widespread applications in sensors, batteries, white light-emitting diodes, photodetectors, phototransistors, etc. Atomically thin two-dimensional quantum dots derived from graphene, layered transition metal dichalcogenide, and phosphorene have sparked researchers' interest with their unique optical and electronic properties, such as a tunable energy bandgap, efficient electronic transport, and semiconducting characteristics. In this review, we provide in-depth analysis of the characteristics of two-dimensional quantum dots materials, their synthesis methods, and opportunities and challenges for novel device applications. This analysis will serve as a tipping point for learning about the recent breakthroughs in two-dimensional quantum dots and motivate more scientists and engineers to grasp two-dimensional quantum dots materials by incorporating them into a variety of electrical and optical fields.

An Effective Optical Dual Gas Sensor for Simultaneous Detection of Oxygen and Ammonia.

The development of a simple, low-cost sensor for the effective sensing of multiple gases in industrial or residential zones has been in high demand in recent days. In this article, we have proposed an optical sensor for the dual sensing of oxygen (O2) and ammonia (NH3) gases, which consists of oxygen and ammonia-sensitive fluorescent dyes coated individually on both sides of a glass substrate. An ethyl cellulose (EC) matrix doped with platinum (II) meso-tetrakis (pentafluorophenyl) porphyrin (PtTFPP) serves as the oxygen-sensing material, whereas the NH3-sensing material includes an eosin Y fluorescent indicator immobilized within a cellulose acetate (CA) matrix. Both the oxygen and ammonia-sensitive materials were excited by the same LED light source with a 405 nm peak wavelength, while the corresponding emissions were detected separately for the selective sensing of the gases under study. The dual gas sensor exhibits maximum sensitivities of around 60 and 20 for oxygen and ammonia gases, respectively. The high sensitivity and selectivity of the proposed optical dual sensor suggests the feasibility of the simultaneous sensing of oxygen and ammonia for practical applications.