Changes In Photoluminescence Research Articles

Lead‐Free Perovskites with Photochromism and Reversed Thermochromism for Repeatable Information Writing and Erasing

AbstractRecently, novel optical information writing strategies have been developed based on fluorescent change of halide perovskites generated by light induced structural transformation. However, to date, the repeatable writing and erasing of fluorescent patterns are still a major challenge. Herein, lead‐free Cs3InCl6:Sb3+ perovskite with photochromism and reversed thermochromism is developed for repeatable information writing and erasing. The original Cs3InCl6:Sb3+ perovskite synthesized by a modified hot‐injection method exhibits green photoluminescence (PL), which is caused by recombination of self‐trapped excitons. After treating with ultrasonication and heating, the green PL gradually turns to blue emission, which is related to surficial Cl vacancies that are generated or exposed due to the desorption of surfactants. Under continuous UV light irradiation, due to the photo repairing effect, the blue emission gradually vanishes, the fluorescent color recovers to green. Based on this photochromic effect, fluorescent patterns are drawn by UV exposure with mask. Moreover, the green PL color can again return to blue by heating at 100 °C. Thus, the photochromism‐induced fluorescent patterns can be simply erased based on the reversed thermochromism effect. Therefore, repeatable optical information writing and thermal erasure are demonstrated based on reversible PL change of Cs3InCl6:Sb3+.

Variable Photoluminescence Intensity Ratio with the Excitation Wavelength in Eu3+-Doped Perovskite-Type Alkaline Earth Zirconates─Possibility of a Unique Visualization of Ultraviolet Light.

Photoluminescence (PL) spectra arising from 4f-4f dipole transitions of Eu3+ doped at both the A and B sites of perovskite-type alkaline earth zirconates obtained at various excitation wavelengths were evaluated. Changes in the excitation wavelength caused obvious differences in the PL intensity ratio of the induced electric dipole (ED) 5D0 → 7F2 transition to the magnetic dipole (MD) 5D0 → 7F1 transition for Eu3+-doped SrZrO3 and CaZrO3, in which only the B site had a center of symmetry. Two charge transfer (CT) bands associated with the excitation of Eu3+ were observed in the spectra of these oxide samples, which arose from the difference in the electronic structure of the Eu-O coordination at the A and B sites. We conclude that simultaneous Eu3+ substitution at sites with and without a center of symmetry, which have different charge transfer energies, induced the observed novel PL changes with a changing excitation wavelength. Our results may enable the development of a new type of ultraviolet light detector.

Compositional Transformation and Impurity‐Mediated Optical Transitions in Co‐Evaporated Cu2AgBiI6 Thin Films for Photovoltaic Applications

AbstractQuaternary copper‐silver‐bismuth‐iodide compounds represent a promising new class of wide‐bandgap (2 eV) semiconductors for photovoltaic and photodetector applications. In this study, vapor phase co‐evaporation is utilized to fabricate Cu2AgBiI6 thin films and photovoltaic devices. The findings show that the properties of vapor‐deposited films are highly dependent upon processing temperature, exhibiting increased pinhole density and transforming into a mixture of quaternary, binary, and metallic phases depending on the post‐deposition annealing temperature. This change in phase is accompanied by an enhancement in photoluminescence (PL) intensity and charge‐carrier lifetime, along with the emergence of an additional absorption peak at high energy (≈3 eV). Generally, increased PL is a desirable property for a solar absorber material, but this change in PL is ascribed to the formation of CuI impurity domains, whose defect‐mediated optical transition dominates the emission properties of the thin film. Via optical pump terahertz probe spectroscopy, it is revealed that CuI impurities hinder charge‐carrier transport in Cu2AgBiI6 thin films. It is also revealed that the predominant performance limitation in Cu2AgBiI6 materials is the short electron‐diffusion length. Overall, the findings pave the way for potential solutions to critical issues in copper‐silver‐bismuth‐iodide materials and indicate strategies to develop environmentally compatible wide‐bandgap semiconductors.

Tailoring Oxidation Responsiveness of Gold Nanoclusters via Ligand Engineering for Imaging Acute Kidney Injury.

Gold nanoclusters (AuNCs) have shown great promise for in vivo imaging because of their definable structure, tunable photoluminescence (PL), and desired renal clearance. However, current understanding of the responsiveness of AuNCs to biological substances is still limited, which may hamper their biomedical applications. Herein, we explore the oxidation responsiveness of near-infrared II (NIR-II) luminescent AuNCs capped with two different ligands, which can be optimized for high-efficiency NIR-II PL imaging of mice acute kidney injury (AKI) featuring high-level peroxynitrite anions (ONOO-). We found that in the presence of ONOO-, N-acetylcysteine-capped AuNCs (NAC-AuNCs) tended to be oxidized more easily than that capped with the macromolecular mercapto-β-cyclodextrin (CDS-AuNCs), resulting in the aggregation of NAC-AuNCs into large-sized assemblies, which was not observed in CDS-AuNCs. The oxidation-triggered morphology, composition, and NIR-II PL changes in NAC-AuNCs were then systematically studied. We finally demonstrated that NAC-AuNCs can be implemented for sensitive NIR-II PL imaging of mice AKI, facilitated by the synergetic in situ AuNC aggregation and decreased glomerular filtration rate (GFR) in the injured kidney, which outperforms the methods solely based on the decreased GFR effect. Therefore, this work highlights the critical significance of ligand engineering in AuNCs and may motivate future design of AuNCs for diverse bioimaging applications.

Changes in the photoluminescence of ultra-weak interlayer coupled MoSe2/PbI2 van der Waals heterostructures

Photo-generated dynamics have been extensively studied in two-dimensional (2D) heterostructures, such as MoSe2/WSe2 and MoSe2/MoS2. Here, we fabricate few-layer PbI2 and monolayer MoSe2 van der Waals (vdW) heterostructures. The excited-wavelength dependent measurements of photoluminescence (PL) and transient dynamic absorption spectra show that there is almost no photo-generated charge transfer between PbI2 and MoSe2. PL changes of MoSe2 are rather dominated by the Fermi level (EF) modulation through the interlayer charge transfer. Density functional theory calculation shows that binding energies in the heterostructures of MoSe2/WSe2 or MoSe2/MoS2 are 2–3 times higher than that of the MoSe2/PbI2 heterostructure, suggesting the weaker interlayer coupling between MoSe2 and PbI2. We propose that the weak interlayer vdW coupling cannot drive the photo-generated interlayer charge transfer while the EF modulation can be achieved through the interlayer charge transfer. The findings will be helpful to fundamental research and applications for novel optoelectronic devices based on 2D material vdW heterostructures.

Effects of Na2O on the optical properties of CdSe QDs embedded in glasses

In this work, effects of Na2O concentration on the precipitation of CdSe QDs in glasses is investigated. It is found that increase in concentration of Na2O reduces the connectivity of the network of glass and decreases the solubility of Se in the glass, leading to the formation of Se-related clusters and lower temperature for the precipitation of CdSe QDs. For glasses containing lower concentration of Na2O, defect-related photoluminescence (PL) is suppressed and the overall PL changes from dual band to narrow band with tunable wavelength in the visible range. For glasses containing higher concentration of Na2O, only dual band PL is observed due to the phase separation upon high temperature heat-treatment. Results reported in this work demonstrate that modulation of the PL properties of QDs in glasses can be accessed by adjusting the composition and structure of glasses.

Machine Learning Enables Prediction of Halide Perovskites' Optical Behavior with >90% Accuracy.

The composition-dependent degradation of hybrid organic-inorganic perovskites (HOIPs) due to environmental stressors still precludes their commercialization. It is very difficult to quantify their behavior upon exposure to each stressor by exclusively using trial-and-error methods due to the high-dimensional parameter space involved. We implement machine learning (ML) models using high-throughput, in situ photoluminescence (PL) to predict the response of Cs y FA1-y Pb(Br x I1-x )3 while exposed to relative humidity cycles. We quantitatively compare three ML models while generating forecasts of environment-dependent PL responses: linear regression, echo state network, and seasonal autoregressive integrated moving average with exogenous regressor algorithms. We achieve accuracy of >90% for the latter, while tracking PL changes over a 50 h window. Samples with 17% of Cs content consistently showed a PL increase as a function of cycle. Our precise time-series forecasts can be extended to other HOIP families, illustrating the potential of data-centric approaches to accelerate material development for clean-energy devices.

Dual‐Modal Iridium‐Based Self‐Immolative Chemosensors for Differential Responses against Reactive Oxygen Species and their Applications to Detect Diabetes

AbstractIn diabetes, platelets are activated by several stimuli, and the activated platelets generate reactive oxygen species (ROS) to induce the aggregation of platelets followed by thrombus formation resulting in various cardiovascular diseases. Therefore, detecting ROS perturbations in platelets can provide a clue to diagnosing diabetes. In this paper, iridium‐based self‐immolative probes (1a‐1c) are reported to monitor perturbations of ROS in the blood through photoluminescence (PL) and electrochemiluminescence (ECL). The probes are designed based on an iridium complex conjugated with phenylboronic acid pinacol ester through carbamate moiety. Three probes contain distinct electron‐withdrawing groups at the ortho‐position in the benzyl linker; thus, subtle reactivity differences are expected against ROS. As expected, all three probes exhibit the most apparent PL changes against hydrogen peroxide (H2O2), but their response patterns against ROS are interestingly distinctive. Utilizing such differential ROS responsive pattern, a discrimination strategy is established using a combination of PL and ECL responses, and discrimination of platelets from diabetic and control rats is successfully demonstrated.

Laser-Patterned Submicrometer Bi2Se3-WS2 Pixels with Tunable Circular Polarization at Room Temperature.

Characterizing and manipulating the circular polarization of light is central to numerous emerging technologies, including spintronics and quantum computing. Separately, monolayer tungsten disulfide (WS2) is a versatile material that has demonstrated promise in a variety of applications, including single photon emitters and valleytronics. Here, we demonstrate a method to tune the photoluminescence (PL) intensity (factor of ×161), peak position (38.4 meV range), circular polarization (39.4% range), and valley polarization of a Bi2Se3-WS2 2D heterostructure using a low-power laser (0.762 μW) in ambient conditions. Changes are spatially confined to the laser spot, enabling submicrometer (814 nm) features, and are long-term stable (>334 days). PL and valley polarization changes can be controllably reversed through laser exposure in a vacuum, allowing the material to be erased and reused. Atmospheric experiments and first-principles calculations indicate oxygen diffusion modulates the exciton radiative vs nonradiative recombination pathways, where oxygen absorption leads to brightening and desorption to darkening.

Photoluminescent carbon nanomaterials for sensing of illicit drugs: focus.

The growth of illicit drugs is a serious social problem, putting great pressure on law enforcement officers to screen numerous suspicious samples at crime scenes. Although commercial colorimetric kits are available, they are limited to common illicit drugs. With increasing numbers of new psychoactive substances in the market, accurate and rapid screening assays are highly demanded. Carbon dots (C-dots) are photoluminescent (PL) carbon nanomaterials with unique properties of excellent stability against salt and photo-irradiation, low blinking, and biocompatibility. They can be prepared easily through various routes from numerous precursors. This Focus provides examples of C-dots based PL assays for screening illicit drugs. The drugs induce PL changes of C-dots mostly through electron transfer and energy transfer. Liquid- and solid-phase PL assays of C-dots can be applied for in-field screening, with advantages of rapidity, low cost, selectivity, and minimum color interference, showing their great commercial potential.

(Invited) Impact of Boron Doping and H2 Annealing on Light Emission from Ge/Si Core-Shell Quantum Dots

We have fabricated Si-QDs with boron-doped Ge core with an areal density as high as ~1011 cm-2 on ultrathin SiO2 and characterized their room temperature photoluminescence (PL) properties. With B doping to the Ge core, stable PL observed in the energy range of 0.62 - 0.85 eV was increased by a factor of ~1.5. Note that a new relatively-narrow component peaked at ~0.64 eV emerges in addition to four components derived from the spectral deconvolution of the PL spectrum of undoped QDs and is attributable to radiative recombination between the first quantized state in the conduction band of the Si clad and the B-acceptor level in the Ge core. With H2 post-anneal at 100°C, the integrated PL intensity of the B-doped QDs was reduced by ~35% and the 0.64 eV component disappeared. With increasing H2 post-anneal temperature up to 350°C, the PL intensity was increased to ~1.4 times the initial intensity before post-annealing, and the 0.64 eV component was recovered. The observed PL changes with post-anneal are attributable to hydrogen-induced passivation of B acceptors at 100°C and thermal dissociation of B-H complex at higher temperatures up to 350°C accompanied with hydrogen passivation of residual dangling bond defects as seen in the undoped case.

Changes in macroscopic and microscopic properties of borosilicate glass irradiated with ions

Borosilicate glass has potential application in the vitrification of high-level waste; therefore, its radiation durability attracts extensive attention. Borosilicate glass samples were irradiated with Xe and Au ions. The samples after irradiation were analyzed by nanoindenter, the Raman, photoluminescence (PL) and infrared spectroscopy. With increase of irradiation dose, the hardness of NBS2 glass samples dropped and then saturated. The changes in PL and infrared spectra of NBS2 glasses samples were deduced. The relation between changes in Raman spectra and those in PL spectra was discussed. The results from PL and infrared spectra revealed the formation of a non-bridging oxygen hole center and transformation of BO4 to BO3 in the NBS2 glass after the irradiation of ions. Relations between the changes in hardness and microstructures of borosilicate glass were discussed.

Optical Imaging of Chemically and Geometrically Controlled Interfacial Diffusion and Redox in 2D van der Waals Space

Molecular motions and chemical reactions occurring in constrained space play key roles in many catalysis and energy storage applications. However, its understanding has been impeded by difficulty in detection and lack of reliable model systems. In this work, we report geometric and chemical manipulation of O2 diffusion and ensuing O2-mediated charge transfer (CT) that occur in the 2D space between single-layer transition metal dichalcogenides (TMDs) and dielectric substrates. As a sensitive real-time wide-field imaging signal, charge-density-dependent photoluminescence (PL) from TMDs was used. The two sequential processes inducing spatiotemporal PL change could be drastically accelerated by increasing the interfacial gap size or introducing artificial defects serving as CT reaction centers. We also show that widely varying CT kinetics of four TMDs are rate-determined by the degree of hydration required for the reactions. The reported findings will be instrumental in designing novel functional nanostructures and devices.

Expanding benzothiadiazole-tetrazole photo-triggered click reaction with chloride ion into reaction-based chloride ion receptor

There is a great increasing need for effective chloride ion receptors due to the widespread distribution and vital role of chloride ion in nature or industrial production. Up to now, most reported molecule receptors (such as chemosensor) reversibly bind chloride ions via specific intermolecular interactions. Although irreversible binding are achieved by a specifically designed reaction that has advantages in terms of high selectivity and sensitivity, the study of reaction-based molecular receptor for chloride ion is currently unexplored. In this work, we designed and synthesized new BTD-tetrazole compounds to study their photo-triggered click reactions with chloride ions. Interestingly, compounds BT1 and BT2 facilely react with chloride ions under UV light irradiation. In the further exploration for the potential application of reaction-based chloride ion molecular receptor, BT1 or BT2 showed obvious absorption and photoluminescence (PL) responses with good selectivity and sensitivity. Moreover, in the response of BT1 or BT2 to chloride ions, the surprising PL changes induced by the hydrogen bonded aggregate of photochemical product (BHc1 or BHc2) provide a new platform to design reaction-based chloride ion receptor.

Chirality luminescent properties of single-walled carbon nanotubes during redox reactions

The optical measurement of single-walled carbon nanotubes (SWNTs) is a useful approach for understanding chirality characteristics because the excitation and emission wavelengths that produce the maximum emission intensity are unique to the chirality of SWNTs. The emission properties of SWNT chirality are useful in various biological applications and are envisaged to be applicable in nanobiosensors. Therefore, it is necessary to detect even small environmental changes, such as redox reactions, and it is important to identify optimal chirality according to the applications. In this study, we focused on the presence of SWNTs with different chiralities within the same SWNT powder, and we investigated the correlation between the rate of change of the emission intensity due to redox reactions and SWNT chirality. We measured the redox change rate of chirality, which was difficult to detect because of the low emission intensity, by increasing the exposure time during photoluminescence (PL) measurement. 0.5 mg of SWNT powder and 1 mL of double-stranded DNA (dsDNA) stock solution were mixed and sonicated using a probe-type sonicator on ice. The supernatant of the prepared dsDNA-SWNT dispersion was stored after centrifugation. Hydrogen peroxide (H 2 O 2 ; final concentration: 0.03%) was added to this dispersion for oxidation, and then, a catechin aqueous solution (final concentration 1.5 μg/mL) was added to the solution to measure PL. The exposure time was 90 s to obtain sufficient emission intensity. The measurement results showed that the magnitude of the rate of change of the PL intensity due to redox reaction was different for each chirality. Focusing on the (8,6) and (9,4) chiralities, which showed a large rate of change, the PL intensity decreased by 57.4% and 54.6% from the initial state, respectively, when H 2 O 2 was added. Subsequently, these values increased by 1024% and 558% with the addition of a catechin aqueous solution, respectively. Furthermore, from the comparison of the PL detection results and optical response characteristics of each chirality, it was observed that the rate of change of the PL intensity of SWNTs during redox reactions using H 2 O 2 and catechin had the strongest correlation with the SWNT diameter. • The exposure time was increased to 90 s to facilitate comparison of PL intensities between chiralities. • The responsiveness of chirality with small emission intensity was detected, which was difficult to detect in previous studies. • The PL change rate during redox using H 2 O 2 and catechin showed the strongest correlation with the SWNTs diameter. • The larger the diameter of SWNTs, the higher will be the PL change rate during redox reactions.

Facilitating Hotspot Alignment in Tip-Enhanced Raman Spectroscopy via the Silver Photoluminescence of the Probe.

A tip-enhanced Raman spectroscopy (TERS) system based on an atomic force microscope (AFM) and radially polarized laser beam was developed. A TERS probe with plasmon resonance wavelength matching the excitation wavelength was prepared with the help of dark-field micrographs. The intrinsic photoluminescence (PL) from the silver (Ag)-coated TERS probe induced by localized surface plasmon resonance contains information about the near-field enhanced electromagnetic field intensity of the probe. Therefore, we used the intensity change of Ag PL to evaluate the stability of the Ag-coated probe during TERS experiments. Tracking the Ag PL of the TERS probe was helpful to detect probe damage and hotspot alignment. Our setup was successfully used for the TERS imaging of single-walled carbon nanotubes, which demonstrated that the Ag PL of the TERS probe is a good criterion to assist in the hotspot alignment procedure required for TERS experiments. This method lowers the risk of contamination and damage of the precious TERS probe, making it worthwhile for wide adoption in TERS experiments.

A QDs Nanocomposites-Based Photoluminescence Ratiometric Method for Selective and Visual Cadmium Detection Combining with Smartphone-Based PL E-Eye

Photoluminescence (PL) sensors based on quantum dots (QDs) are difficult to achieve exact detection in sample waters. In this paper, polyvinyl alcohol (PVA) based CdTe/ZnS/CdS QDs and fluorescein isothiocyanate (FITC) fluorophores were used to build a ratiometric PL sensor. Combining with the homemade smartphone-based PL E-eye, the Cd2+ exact detection can be achieved. PVA was used to connect QDs and FITC fluorophores without unnecessary ligand exchange and purification. For QDs fluorophore, ethylenediaminetetraaceticacid (EDTA) was used on the surface to induce the specifically Cd2+ recognition site. For FITC fluorophore, the PL remains unchanged in this experiment. Thus, the ratio of two fluorophores can be used to provide a built-in correction. The PL changes with the increase of Cd2+ concentrations could be displayed as a visual color change on the smartphone. Further quantitative analysis could be carried out by the RGB value of the picture through the App in less than 1 min The ratio of R/G is linear to Cd2+ concentration in the range of 1–2000 μg l−1 with a low LOD of 0.057 μg l−1 (S/N). Compared with traditional analysis methods, the PL ratiometric method with PL E-eye is portable, rapid, visible and highly selective especially in discriminate Cd2+ from Zn2+.

Photoluminescence Imaging of Whole Zircon Grains on a Petrographic Microscope—An Underused Aide for Geochronologic Studies

The refractory nature of zircon to temperature and pressure allows even a single zircon grain to preserve a rich history of magmatic, metamorphic, and hydrothermal processes. Isotopic dating of micro-domains exposed in cross-sections of zircon grains allows us to interrogate this history. Unfortunately, our ability to select the zircon grains in a heavy mineral concentrate that records the most geochronologic information is limited by our inability to predict internal zonation from observations of whole grains. Here we document the use of a petrographic microscope to observe and image the photoluminescence (PL) response of whole zircon grains excited under ultraviolet (UV) light, and the utility of this PL response in selecting grains for geochronology. While zircon fluorescence has long been known, there is limited documentation of its utility for and application to geochronologic studies. Our observations of zircon from an un-metamorphosed igneous rock, two meta-igneous rocks, and a placer deposit show that variations in the PL color are readily observable in real-time, both among grains in a population of zircons and within single grains. Analyses of cross-sections of the same grains demonstrate that the changes in PL correlate with zoning in backscattered electron (BSE) and cathodoluminescence (CL) images as well as with changes in U + Th concentration and spectroscopic proxies for radiation damage. In other words, the whole grain PL provides a low-resolution preview of the U + Th zoning expected in a cross-sectioned grain. We demonstrate the usefulness of this “preview” in identifying and selecting the subset of zircon grains in a heavy mineral separate that has metamorphic rims of sufficient width to date by secondary ionization mass spectrometry (SIMS). The data are also used to place preliminary constraints on the age and U + Th concentrations at which a yellow PL response is observed in natural samples. The PL response of zircon is well-known among spectroscopists, and these simple applications demonstrate several ways in which the response might be more effectively used by geochronologists.

Photoluminescence label-free immunosensor for the detection of Aflatoxin B1 using polyacrylonitrile/zinc oxide nanofibers.

The precise and rapid detection of hazardous molecules, microorganisms, pollutants, and toxins currently remains a global challenge. Aflatoxin B1 (AFB1) is a toxic and dangerous product of fungi that considered as cancerogenic, mutagenic, and immunosuppressive for humans and animals. Therefore, the screening of AFB1 in food and beverages plays an important role in preventing foodborne illnesses. In this study, AFB1 molecules were detected in a microfluidic device with integrated polyacrylonitrile/zinc oxide (PAN/ZnO) nanofibers fabricated via a combination of the electrospinning, and atomic layer deposition (ALD) techniques. The structural and optical analyses of PAN/ZnO nanofibers were performed and samples with the most suitable properties were utilized for AFB1 detection. In order to obtain the biorecognition layer towards AFB1, PAN/ZnO samples were modified by (3-Aminopropyl) triethoxysilane (APTES), and glutaraldehyde (GA), bovine serum albumin (BSA) and monoclonal antibodies (Anti-AFB1). Subsequently, photoluminescence (PL)-based immunosensor was integrated into a microfluidic cell and tested for AFB1 detection. The mechanism of PL changes caused by AFB1 & Anti-AFB1 complex formation was analyzed and developed. The proposed approach enables the detection of AFB1 with the lowest concentration (LOD) of about 39pg/ml, while the sensitivity range was evaluated as 0.1-20ng/ml. The obtained values of LOD and sensitivity, as well as the simplicity of the detection method, make this approach a prospect for further application.

Stability and band gap engineering of silica-confined lead halide perovskite nanocrystals under high pressure

SiO2 is the major mineral substance in the upper mantle of the earth. Therefore, studies of the silica-coated materials under high-pressure are essential to explore the physical and chemical properties of the upper mantle. The silica-confined CsPbBr3 nanocrystals (NCs) have recently attracted much attention because of the improved photoluminescence (PL) quantum yield, owing to the protection of silica shell. However, it remains considerable interest to further explore the relationship between optical properties and the structure of CsPbBr3@SiO2 NCs. We systemically studied the structural and optical properties of the CsPbBr3@SiO2NCs under high pressure by using diamond anvil cell (DAC). The discontinuous changes of PL and absorption spectra occurred at ∼1.40 GPa. Synchrotron X-ray diffraction (XRD) studies of CsPbBr3@SiO2 NCs under high pressure indicated an isostructural phase transformation at about 1.36 GPa, owing to the pressure-induced tilting of the Pb-Br octahedra. The isothermal bulk moduli for two phases are estimated about 60.0 ​GPa and 19.2 GPa by fitting the equation of state. Besides, the transition pressure point of CsPbBr3@SiO2 NCs is slightly higher than that of pristine CsPbBr3 NCs, which attributed to the buffer effect of coating silica shell. The results indicate that silica shell is able to enhance the stabilization without changing the relationship between optical properties and structure of CsPbBr3 NCs. Our results were fascinated to model the rock metasomatism in the upper mantle and provided a new ‘lithoprobe’ for detecting the upper mantle.