Photoluminescence Response Research Articles

Thermally activated delayed fluorescence and high-contrast mechanochromism of anthrone-based donor-acceptor systems.

The development of materials that emit in the deep-red to near-infrared region of the spectrum has attracted significant attention due to their potential as optical sensing and imaging reagents in biology. Herein, we report the synthesis and optoelectronic characterization of four anthraquinone-based emitters, T-tBuCz-AQ, T-MeOCz-AQ, C-tBuCz-AQ, and C-MeOCz-AQ, and two pyrazoloanthrone-based emitters, tBuCz-PA and DMAC-PA. Depending on the donor, these compounds emit in the spectral range between 640 and 750nm in the neat film, while the emission of the 10 wt% doped films in poly(methyl methacrylate) (PMMA) is blue-shifted between 600 and 700nm and has low photoluminescence quantum yields between 2.6% and 6.6%. Of these compounds, T-tBuCz-AQ, T-MeOCz-AQ, and C-tBuCz-AQ exhibited thermally activated delayed fluorescence (TADF) in 10 wt% doped films in PMMA, while the crystals of T-tBuCz-AQ also showed TADF. Compound tBuCz-PA showed a high-contrast and reversible photoluminescence (PL) response upon mechanical grinding and hexane fuming.

Inkjet‐Printed and Nanopatterned Photonic Phosphor Motifs with Strongly Polarized and Directional Light‐Emission

AbstractHerein a versatile and scalable method to prepare periodically corrugated nanophosphor surface patterns displaying strongly polarized and directional visible light emission is demonstrated. A combination of inkjet printing and soft lithography techniques is employed to obtain arbitrarily shaped light emitting motifs. Such predesigned luminescent drawings, in which the polarization and angular properties of the emitted light are determined and finely tuned through the surface relief, can be used as anti‐counterfeiting labels, as these two specific optical features provide additional means to identify any unauthorized or forged copy of the protected item. The potential of this approach is exemplified by processing a self‐standing photoluminescent quick response code whose emission is both polarized and directionally beamed. Physical insight of the mechanism behind the directional out‐coupled photoluminescence observed is provided by finite‐difference time‐domain calculations.

Understanding Oligonucleotide Hybridization and the Role of Anchoring on the Single-Walled Carbon Nanotube Corona Phase for Viral Sensing Applications

Semiconducting single-walled carbon nanotubes (SWCNTs) with tailored corona phases (CPs), or surface adsorbed molecules, have emerged as a promising interface for sensing applications. The adsorption of an analyte can be specifically transduced as a modulation of their band gap near-infrared (nIR) photoluminescence (PL). One such CP ideal for this purpose is single-stranded DNA (ssDNA), where subsequent sequence dependent hybridization can result in PL emission wavelength shifts. Due to ssDNA adsorption to the SWCNT surface, the resultant non-canonical hybridization and its effect on SWCNT photophysical properties are not well understood. In this work, we study 20- and 21-mer DNA and RNA hybridization on the complementary ssDNA-SWCNT CP in the context of nucleic acid sensing for SARS-CoV-2 sequences as model analytes. We found that the van’t Hoff transition enthalpy of hybridization on SWCNT CP was -11.9 kJ mol-1, much lower than that of hybridization in solution (-707 kJ mol-1). We used SWCNT solvatochromism to calculate the solvent exposed surface area to indicate successful hybridization. We found that having a 30-mer anchor region in addition to the complementary region significantly improved PL response sensitivity and selectivity, with (GT)15 anchor preferred for RNA targets. Coincubation of ssDNA-SWCNT with analyte at 37°C resulted in faster hybridization kinetics without sacrificing specificity. Other methods aimed to improve CP rearrangement kinetics such as bath sonication and surfactant additions were ineffective. We also determined that target sequence choice is important as secondary structure formation in target is negatively correlated with hybridization. Best performing CPs showed detection limits of 11 nM and 13 nM for DNA and RNA targets respectively. Finally, we simulated sensing conditions using saliva environment, showing sensor compatibility in biofluids. In total, this work elucidates key design features and processing to enable sequence specific hybridization on ssDNA-SWCNT CP.

One-Pot Synthesis of CdTe/ZnS Quantum Dots and their Physico-Chemical Characterization.

A known property of quantum dots (QDs) is their characteristic luminescence, which would make it possible to detect different types of cancers after being functionalized with some type of biological molecule. For this reason, in the present investigation a methodological analysis of the physicochemical characteristics of the CdTe/ZnS core/shell QDs was carried out, using techniques such as Optical Absorbance Spectroscopy (UV-Vis), Molecular Fluorescence, Fourier Transform Infrared Spectroscopy (FT-IR), Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Zeta Potential that allowed to verify the photoluminescent effectiveness of these semiconductor nanocrystals as an alternative to conventional techniques currently used for the detection of specific cancers smaller than 1cm. The study consisted of theoretically determining the bandgap energy, the size of the nanocrystals and the molar absorptivity from the wavelength value for the maximum intensity of the excitonic peak. It was also possible to verify the maximum intensity for each sample and thus evaluate its photoluminescent response, as well as it was possible to determine the charge distribution, the hydrodynamic size and the surface composition of each quantum dot. The results obtained correspond to what has been reported in the literature, which makes them good candidates for the detection of cancer in precancerous stages.

Machine learning-assisted photoluminescent sensor array based on gold nanoclusters for the discrimination of antibiotics with test paper

Antibiotic residues accumulation in the environment endangers ecosystems and human health. There is an urgent need for a facile and efficient strategy to detect antibiotics. Here, we report a photoluminescent sensor array based on protein-stabilized gold nanoclusters (AuNCs) for the detection of two families of antibiotics, tetracyclines and quinolones. The nanoclusters were synthesized with bovine serum albumin (BSA) and ovalbumin (OVA), respectively. They had different interactions with seven kinds of antibiotics and exhibited diverse photoluminescence (PL) responses, which were analyzed by linear discriminant analysis and ExtraTrees algorithms. The sensor array performed well in both classification and quantification of seven antibiotics. And the quantitative results of all antibiotics obtained R2 of no less than 0.99 at 0–100 μM when using suitable regression models. Additionally, the sensor array was able to distinguish antibiotic mixtures and multiple interfering substances, and it also kept 100% classification accuracy in river water samples. Moreover, test paper assisted by a smartphone was applied for quick detection of antibiotics, with good performance in both HEPES buffer and river water. These studies reveal great potential for the point-of-use analysis of antibiotics in environmental monitoring.

Machine Learning-Mediated Ultrasensitive Detection of Citrinin and Associated Mycotoxins in Real Food Samples Discerned from a Photoluminescent Carbon Dot Barcode Array.

Economically viable remote sensing of foodborne contaminants using minimalistic chemical reagents and simultaneous automation calls for a concrete integration of a chemical detection strategy with artificial intelligence. In a first of its kind, we report the ultrasensitive detection of citrinin and associated mycotoxins like aflatoxin B1 and ochratoxin A using an Alizarin Red S (ARS) and cystamine-derived carbon dot (CD) that aptly amalgamate with machine learning algorithms for automation. The photoluminescence response of the CD as a function of various solvents and pH is used to generate array channels that are further modulated in the presence of the mycotoxins whose digital images were acquired to determine pixelation, essentially creating a barcode. The barcode was fed to machine learning algorithms that actualize and intertwine convoluted databases, demonstrating Extreme Gradient Boosting (XGBoost) as the optimized model out of eight algorithms tested. Spiked samples of wheat, rice, gram, maize, coffee, and milk were used to evaluate the testing model where an exemplary accuracy of 100% even at 10 pmol of mycotoxin concentration was achieved. Most importantly, the coexistence of mycotoxins could also be detected through the CD array and XGBoost synergy hinting toward a broader scope of the developed methodology for smart detection of foodborne contaminants.

Multifunctional Roles of Dihydrotetrazine-Decorated Zr-MOFs in Photoluminescence and Colorimetrism for Discrimination of Arsenate and Phosphate Ions in Water.

The high chemical and structural stabilities of zirconium (Zr)-based metal-organic frameworks (MOFs) in aquatic media make them ideal candidates for wastewater treatment. Rational decoration or Zr-MOFs with functional groups can significantly extend their application in this area. In this work, two well-known Zr-MOFs, UiO-66 and MIL-140-A, were functionalized with dihydrotetrazine function to increase their capability in water treatment. Investigations reveal that these two dihydrotetrazine (DHTZ)-functionalized MOFs, namely UiO-66(Zr)-DHTZ and MIL-140(Zr)-DHTZ, can be applied as a two-component array for highly selective and sensitive discrimination of arsenate (AsO43-) and phosphate (PO43-) ions in water in the presence of other anions. Photoluminescence (PL) tests using UiO-66(Zr)-DHTZ show that this MOF can detect these two anions via a ratiometric response, 1.74 for arsenate and 1.84 for phosphate at 2 μM, with superior detection limits (7.2 × 10-8 M for AsO43- and 4.3 × 10-8 M for PO43-). The ratiometric PL response of UiO-66(Zr)-DHTZ toward arsenate and phosphate anions arises possibly from the arsenate-dihydrotetrazine hydrogen bonding. In the next step, colorimetric tests using MIL-140(Zr)-DHTZ were conducted to discriminate the arsenate from phosphate with a very low detection limit at nanomolar level. This MOF undergoes a yellow-to-pink color change in the presence of arsenate ions, while no color change is observed in the presence of phosphate. This color change is observed through conversion of dihydrotetrazine sites inside the pores of MIL-140(Zr)-DHTZ into tetrazine. Altogether, the PL response of UiO-66(Zr)-DHTZ is originated from the hydrogen bond-donating/accepting character of DHTZ function, while the colorimetric response of MIL-140(Zr)-DHTZ is based on the chemical conversion of DHTZ function. This work clearly shows that the decoration of Zr-based MOFs with multicharacter functional groups can develop their application in wastewater treatment as multipurpose platforms.

Stability of the Photoluminescent Response on Hydroxyapatite/Multi-Walled Carbon Nanotube Composites

The application of hydroxyapatite (HAp)/multi-walled carbon nanotube composites in the medical area as coatings in prosthetics has been widely used because the carbon nanotubes reinforce the mechanical properties of hydroxyapatite. Despite that, their photoluminescent properties have not been studied, nor has the effect of different amounts of multi-walled carbon nanotubes on this property or what happened with their response with time. This work demonstrated that the photoluminescent response of HAp and HAp/multi-walled carbon nanotubes functionalized with oxygen groups (OMWCNT) composites was stabilized over time. The evaluated parameters were: three different amounts of OMWCNT (15, 25, and 35 mg) and two different thermal treatment temperatures (250 and 400 °C); all the samples were measured twice, after preparation and over a year after. The results indicated that over time the photoluminescent response is stabilized due to the passivation of surface defects, independently of the amount of OMWCNT used and the thermal treatment. In the end, the photoluminescent properties of these composites will extend their utilization in the medical area or open the door to new applications.

Manipulation of luminescence activity by interfacial engineering via surface treatment of TiO2 nanorods in the core/shell/mixed halide CH3NH3PbI3-xClx perovskite heterostructures

Efficient charge transfer between the various layers in a solar cell requires proper modification of interfaces. Multi-step hydrothermal processing have been adopted for the fabrication of Core/shell TiO2/SrTiO3 nanorod array on the Fluorine-doped Tin Oxide and TiO2 surfaces. Nanorods were treated with strontium for surface passivation via hydrothermal technique which is found to be critical in tuning the optoelectronic properties. For individual layers in thin films, various experimental techniques were used to study structural, morphological, optical and spectroscopic properties. Raman spectroscopy, reveal presence of rutile and anatase phase for TiO2 nanorods which corelates with the crystal structure of compact layer and nanorods. Afterwards a perovskite layer was deposited on top of nanorods to study photo-luminescence response which successfully revealed that strontium treatment of nanorods suppresses the recombination of charge carriers. The observations and results discussed in this article will be helpful in improving the optoelectronic properties of the material and could lead to improved efficiency of perovskite solar cells.

Oxygen sensing behavior modulation of tetranuclear copper iodide hybrid materials using ligand engineering

Copper iodide hybrid materials (CIHMs) are receiving great attention as promising luminescent materials. Their structural diversity can be enriched by design and selection of organic ligands, associated with corresponding photophysical properties. However, the role of ligands in modulating sensing performance of CIHMs stays rarely revealed. Here, we demonstrate the O2 sensing capability of four tetranuclear CIHMs and reveal the impact of ligands on their different triplet quenching process. Oxygen sensing films were prepared using the selected CIHMs. The study results reveal their oxygen sensing behaviors with wide linear photoluminescence (PL) responses in the range from 0% to 100% for gaseous oxygen, and the corresponding PL quenching ratios of 12.14, 11.30, 2.90 and 2.26 (0–100% O2), respectively. In addition, all the CIHMs showed rapid and reversible response to oxygen within 10 s. Through investigating the time-resolved luminescence spectra, 1H NMR and corresponding crystal structures of the CIHMs in N2 and O2 environments, we highlight that specific crystal stacking patterns caused by different ligands play a major role in their distinct oxygen sensing behaviors. It indicates that the sensing performance of the CIHMs can be regulated through functionalization of the ligands which inspires new insights into their more extensive application.

Steady-State Characterization for Capture and Escape Lifetimes of 2-D Electron Gas in Light-Emitting Transistors

Quantum-well-based heterojunction bipolar light-emitting transistors (HBLETs or LETs) could work as candidate devices in optical communication and optoelectronic integrated circuits (OEICs) due to their multiport operation properties. The recombination process and capture-escape dynamics of carriers limit the device modulation bandwidth. The knowledge of capture and escape lifetimes is necessary to improve bandwidths. Here, we present a steady-state procedure rather than dynamic ones such as time-resolved photoluminescence (TRPL) or small-signal response to characterize the two lifetimes of LETs. On the experimental side, we perform dc measurements to investigate the electrical characteristics of the base–emitter (BE) junction of LETs. Theoretically, we formulate the charge-controlled model with continuity equations for electron concentrations in unbound and bound subbands of the quantum well (QW). The related capture and escape lifetimes are extracted with analytical expressions and the current gains of LETs. In the end, we verify our model by comparing the measured bandwidths to the unity gain bandwidths of this study.

Folic acid-derived luminescent carbon dots: Effect of Ag inclusion and switch ON sensing of sulfide ions

One of the aesthetic concerns of the scientific community is to ensure all people have access to safe drinking water. Sulfide ion is considered as a public health risk-worthy constituent in water. The present work investigates the effect of localized surface plasmon resonance (LSPR) of silver nanoparticles (AgNP) on the photoluminescence response of folic acid-derived carbon nanodots (CD) and their application towards sulfide ion detection. Herein, CD are grown on the surface of AgNP, causing an absorption band centered at ∼ 400 nm due to LSPR. AgNP effectively quench the luminescence of CD through the static quenching mechanism. The Ag-CD system is designed as a simple and selective sensor for sulfide ions in water in a linear range of 0.8–1.5 µM with a Limit of Detection (LOD) of 50 nM and a Limit of Quantification (LOQ) of 170 nM. The ion selectivity for sensing was carried out in accordance with the Hard and Soft – Acids and Bases theory and its predictions. The practical applicability of the sensor was tested by determining the spiked sulfide ion concentrations in pond water and tap water, which produced an adequate outcome.

Tuning the Luminescence Response of an Air-Hole Photonic Crystal Slab Using Etching Depth Variation.

Detailed studies of the luminescent properties of the Si-based 2D photonic crystal (PhC) slabs with air holes of various depths are reported. Ge self-assembled quantum dots served as an internal light source. It was obtained that changing the air hole depth is a powerful tool which allows tuning of the optical properties of the PhC. It was shown that increasing the depth of the holes in the PhC has complex influences on its overall photoluminescence (PL) response due to the simultaneous influences of counteracting factors. As a result, the maximal increase in the PL signal of more than two orders of magnitude was obtained for some intermediate, but not full, depth of the PhC's air holes. It was demonstrated that it is possible to engineer the PhC band structure in such a way as to construct specific states, namely bound states in continuum (BIC), with specially designed dispersion curves being relatively flat. In this case, such states manifest themselves as sharp peaks in the PL spectra, and have high Q-factors which are larger than those of radiative modes and other BIC modes without such a flat dispersion characteristic.

α-Fe2O3/CeO2 S-scheme heterojunction photocatalyst for enhanced photocatalytic H2 evolution

High photo-stability and effective charge separation are pivotal for hydrogen production over the photocatalysts through solar energy. Here mesoporous CeO2 nanorods were hydrothermally synthesized using cetyltrimethyl ammonium bromide and tetrapropylammonium hydroxide as the template to construct the novel S-scheme heterojunction α-Fe2O3/CeO2 photocatalyst. The obtained heterojunction Fe2O3/CeO2 photocatalyst exhibited outstanding enhanced H2 evolution under visible illumination. The XRD results indicated that the Fe2O3/CeO2 nanocomposites revealed rhombohedral α-Fe2O3 and cubic CeO2 structures without impurities. TEM images revealed the formation of CeO2 nanorods with 400 nm length and 20 nm width decorated with Fe2O3 NPs (10 nm). The optimized S-scheme Fe2O3/CeO2 nanocomposites displayed a superior photocatalytic H2 evolution rate of 2973.2 µmolg−1h−1, which was promoted 5.43 folds greater than that of CeO2 nanorods (547.05 µmolg−1h−1). The electron transport channels in S-scheme Fe2O3/CeO2 nanocomposites interfacial junctions facilitated the directional migration spatial and separation of photocarriers. The H2 evolution rate over the obtained Fe2O3/CeO2 photocatalyst was significantly promoted due to its synergistic effect, porous architecture, oxygen vacancies, small particle size and high visible light absorption ability. There was no decrease in the H2 evolution rate after five cycles of photocatalytic H2 evolution, which could verify the durability and stability of the Fe2O3/CeO2 nanocomposite. The photoluminescence (PL) and electrophotochemical responses were conducted to determine the charge carriers separation rate and understand the photocatalytic mechanism.

Novel approach to increase chemosensing ability of fluorophore via cross-linked hydrogel film formation

2,5-Bis(4-hydroxy-3-methoxyphenyl)thiazolo[5,4-d]thiazole (MPhTT) fluorophore as a donor–acceptor-donor (D-A-D) type sensor molecule is synthesized for further investigation of sensing ability of the molecule towards various anions and cations. The MPhTT molecule with strong photoluminescence (PL) has been determined to be sensitive against anions with an effective deprotonation mechanism. MPhTT molecule has been demonstrated to have a limited ability to recognize anions by PL response in the solution while selectively sensitive against CN− anion after being embedded into filter paper. Moreover, metal cations detection in the solution is impossible with the MPhTT fluorophore. The use of MPhTT dye as a cross-linker to prepare highly emissive PVA hydrogel films resulted in a reusable chemosensor for acid, base, CN− anion, and metal cations. The mechanical properties of the films and their swelling behavior have also been investigated to show their water-responsive mechanical properties and water intake ability for possible biomedical applications.These findings indicate that increasing the chemosensing ability of the dye by cross-linking of polymers can be used for many fluorophores as an innovative approach. The films with extended mechanical properties can be used for wound dressing, biosensors, moisture sensors, and many other applications.

Aerial Photoluminescence Imaging of Photovoltaic Modules

On‐site imaging of modules in photovoltaic (PV) systems requires contact‐free techniques with high throughput and low cost for commercial relevance. Photoluminescence imaging satisfies these requirements, but it has so far not been used for aerial imaging. Such a system faces unique engineering and operating challenges, including the need to mount a light source on the drone and identifying module defects from images taken under low‐ and nonuniform irradiance. Herein, in‐house developed photoluminescence aerial imaging (PLAI) setup is presented and it is demonstrated that it can be used to identify defects even with a difference of excitation intensity of up to 50%. The setup consists of a hexacopter aerial drone equipped with an illumination unit and a near‐infrared camera. The unit is capable of partially illuminating full‐sized modules at night and capturing the photoluminescence response. In the maiden flight, a throughput of 13.6 PV modules per minute is achieved, and a throughput of 300 PV modules per minute is feasible. It is shown that the setup can be used to detect and identify cracks and potential induced degradation with high levels of confidence. These findings are verified by cross correlation and comparing captured photoluminescence images to electroluminescence images taken indoors.

Optical and photoluminescence response driven by sintering temperature in LaFeO3 nano-perovskites

Optical and photoluminescence response driven by sintering temperature in LaFeO3 nano-perovskites

Chirality-specific Near-infrared Photoluminescent Responses of Single-walled Carbon Nanotubes to Detect Papain Adsorption Assisted by the Use of DNA and Frustules

Chirality-specific Near-infrared Photoluminescent Responses of Single-walled Carbon Nanotubes to Detect Papain Adsorption Assisted by the Use of DNA and Frustules

Graphene Oxide: Key to Efficient Charge Extraction and Suppression of Polaronic Transport in Hybrids with Poly (3-hexylthiophene) Nanoparticles.

Nanoparticles (NPs) of conjugated polymers in intimate contact with sheets of graphene oxide (GO) constitute a promising class of water-dispersible nanohybrid materials of increased interest for the design of sustainable and improved optoelectronic thin-film devices, revealing properties exclusively pre-established upon their liquid-phase synthesis. In this context, we report for the first time the preparation of a P3HTNPs-GO nanohybrid employing a miniemulsion synthesis approach, whereby GO sheets dispersed in the aqueous phase serve as a surfactant. We show that this process uniquely favors a quinoid-like conformation of the P3HT chains of the resulting NPs well located onto individual GO sheets. The accompanied change in the electronic behavior of these P3HTNPs, consistently confirmed by the photoluminescence and Raman response of the hybrid in the liquid and solid states, respectively, as well as by the properties of the surface potential of isolated individual P3HTNPs-GO nano-objects, facilitates unprecedented charge transfer interactions between the two constituents. While the electrochemical performance of nanohybrid films is featured by fast charge transfer processes, compared to those taking place in pure P3HTNPs films, the loss of electrochromic effects in P3HTNPs-GO films additionally indicates the unusual suppression of polaronic charge transport processes typically encountered in P3HT. Thus, the established interface interactions in the P3HTNPs-GO hybrid enable a direct and highly efficient charge extraction channel via GO sheets. These findings are of relevance for the sustainable design of novel high-performance optoelectronic device structures based on water-dispersible conjugated polymer nanoparticles.

Analysis of compositional differences between commercial rice grains by the study of the photoluminescence response

This paper presents the optical characterization of five commercial classes of rice: two classes of white rice, one fortified, one integral, and one parboiled. The differences between the line shapes of the photoluminescence spectra of rice grains and the contribution of its components, starch, fat, and ash, to the rice spectrum were discussed. The fat contributes to rice emission at wavelengths 676 nm and 715 nm, while the starch components contribute at low wavelengths with maxima at 552 and 591 nm. As for the ash, the photoluminescence spectra are of low intensity for all samples, with no significant incidence in the rice photoluminescence spectrum. However, the ashes of the fortified rice and parboiled rice show structures in the line shape at 744, 774, 842, and 881 nm, attributed to minerals not present in the other classes of rice. Additionally, we present these comparisons on absorption spectra in the infrared region; it was observed that there are differences between the white classes of rice and the classes of rice with husk; a high similarity between the absorption spectrum of rice and its starch was also observed, masking the contribution of fat and ash, thus validating the sensitivity of the photoluminescence technique.