Signal Intensity Enhancement Research Articles

Examination of Radiation Belt Dynamics During Substorm Clusters: Activity Drivers and Dependencies of Trapped Flux Enhancements

AbstractDynamical variations of radiation belt trapped electron fluxes are examined to better understand the variability of enhancements linked to substorm clusters. Analysis is undertaken using the Substorm Onsets and Phases from Indices of the Electrojet substorm cluster algorithm for event detection. Observations from low earth orbit are complemented by additional measurements from medium earth orbit to allow a major expansion in the energy range considered, from medium energy energetic electrons up to ultra‐relativistic electrons. The number of substorms identified inside a cluster does not depend strongly on solar wind drivers or geomagnetic indices either before, during, or after the cluster start time. Clusters of substorms linked to moderate (100 nT < AE ≤ 300 nT) or strong AE (AE ≥ 300 nT) disturbances are associated with radiation belt flux enhancements, including up to ultra‐relativistic energies by the strongest substorms (as measured by strong southward Bz and high AE). These clusters reliably occur during times of high speed solar winds streams with associated increased magnetospheric convection. However, substorm clusters associated with quiet AE disturbances (AE ≤ 100 nT) lead to no significant chorus whistler mode intensity enhancements, or increases in energetic, relativistic, or ultra‐relativistic electron flux in the outer radiation belts. In these cases the solar wind speed is low, and the geomagnetic Kp index indicates a lack of magnetospheric convection. Our study clearly indicates that clusters of substorms occurring outside of high speed wind streams are not by themselves sufficient to drive acceleration, which may be due to the lack of pre‐cluster convection.

Finite-difference time-domain to screen Au NPs as SERS active substrate for the sensitive determination of prohibited drugs in fish via solvent cleaning.

Surface enhanced Raman spectroscopy (SERS), as a molecule-specific method using plasmonic nanostructures to significantly enhance signal intensity, has been employed in various fields. In our study, we investigated the size effect of gold nanoparticles (Au NPs) on surface plasmon response by finite-difference time-domain (FDTD) simulation. In addition, SERS experiments, using the same concentrations of crystal violet (CV), were also carried out to confirm the simulation results. On this basis, the size of citrate-stabilized Au NPs (∼100 nm) was controlled by a seed-mediated growth, thus providing great electromagnetic field enhancement for SERS detection of CV in fish. Methanol solvent cleaning along with high speed centrifugal separation was developed, which could not only remove lipids in fish, but also produce hot spots via induced aggregation of Au NPs. The SERS detection limit of CV in fish could be less than 1 ppb. Such cost-effective and facile routes will be attractive for the trace detection of various analytes in complex matrices.

Tracking Stress Granule Dynamics in Live Cells and In Vivo with a Small Molecule.

Because of the lack of facile and accurate methods to track stress granule (SG) dynamics in live cells and in vivo, in-depth studies of the biological roles of this attractive membraneless organelle have been limited. Herein, we report the first small-molecule probe, TASG, for the selective, convenient and real-time monitoring of SGs. This novel molecule can simultaneously bind to SG RNAs, the core SG protein G3BP1, and their complexes, triggering a significant enhancement in fluorescence intensity, making TASG broadly applicable to SG imaging under various stress conditions in fixed and live cells, ex vivo and in vivo. Using TASG, the complicated endogenous SG dynamics were revealed in both live cells and C. elegans. Collectively, our work provides an ideal probe that has thus far been absent in the field of SG investigations. We anticipate that this powerful tool may create exciting opportunities to investigate the underlying roles of SGs in different organisms.

Investigation of Adsorption Behavior of Anticancer Drug on Zinc Oxide Nanoparticles: A Solid State NMR and Cyclic Voltammetry (CV) Analysis.

The present study aims to comprehend the adsorption behavior of a set of anticancer drugs namely 5-fluorouracil (5-FU), doxorubicin and daunorubicin on ZnO nanoparticles (ZnO NPs) proposed as drug delivery systems employing solid state (ss) NMR, FTIR and Cyclic Voltammetry (CV) analysis. FTIR and 1H MAS ssNMR data recorded for bare ZnO nanoparticle confirmed the presence of adsorbed -OH groups on the surface. 13C CP-MAS NMR spectra recorded for free and ZnO surface adsorbed drug samples exhibited considerable line broadening and chemical shift changes that complemented our earlier report on UV-DRS and XRD data of surface adsorption in case of 5-FU. Moreover, a remarkable enhancement of 13C signal intensity in case of loaded 5-FU was observed. This clearly indicated rigid nature of the drug on the surface allowing efficient transfer of 1H polarization from the hetero nitrogen of 5-FU to ZnO to form surface hydroxyl (-OH) groups and the same has been observed in the quantum chemical calculations. To further analyze the motional dynamics of the surface adsorbed 5-FU, longitudinal relaxation times (T1) were quantified employing Torchia method that revealed significant enhancement of 13C relaxation rate of adsorbed 5-FU. The enhanced rate suggested an effective role of quadrupolar contribution from 67Zn to the 13C relaxation mechanism of ZnO_5-FU. The heterogeneous rate constant (khet), average free energy of activation (∆G≠) and point of zero charge (PZC) measured for free and drug loaded ZnO NPs samples using CV further support the SS-NMR results.

Heat-induced antigen retrieval in fluorescence in situ hybridization: An effective approach enhancing signal intensity in poor-quality FFPE sections.

Fluorescence in situ hybridization (FISH) serves as an ancillary tool for assessing chromosomal abnormalities and is important in differential diagnoses and treatment decisions. In clinical practice, pathologists encounter unsatisfactory formalin-fixed paraffin-embedded (FFPE) sections exhibiting weak fluorescence signals, mostly due to inappropriate tissue processing or preservation, leading to interpretation difficulties. For the present study, FFPE samples for which conventional FISH failed were collected. Instead of a pretreatment step using a commercial kit, heat-induced antigen retrieval (HIAR) was introduced using either citrate buffer or Tris-EDTA buffer, while the subsequent experimental workflow remained unchanged. After HIAR-assisted FISH, the hybridization efficiency and signal intensity were markedly enhanced and no difference in signal adequacy was observed when comparing the effect of the two AR solutions. The present study demonstrated that HIAR is a reliable tool for FISH, particularly for poor-quality FFPE sections yielding weak or no fluorescence signals in the conventional analysis.

Seeing more with less: virtual gadolinium-enhanced glioma imaging

MRI is the main modality to diagnose and monitor the evolution and treatment of brain tumours. Radiological tumour grading relies on evidence of abnormal blood–brain barrier permeability, achieved by intravenous injection of gadolinium-based contrast agents (GBCA), leading to enhanced signal intensity on T1-weighted images. The current goal in glioma surgery is resection of the enhancing tumour parts and the response assessment in neuro-oncology (RANO) criteria for monitoring glioma treatment response heavily rely on the demonstration of recurring or enlarging enhancing tumour.

Electric Field Tunability of Photoluminescence from a Hybrid Peptide-Plasmonic Metal Microfabricated Chip.

Enhancement of fluorescence through the application of plasmonic metal nanostructures has gained substantial research attention due to the widespread use of fluorescence-based measurements and devices. Using a microfabricated plasmonic silver nanoparticle–organic semiconductor platform, we show experimentally the enhancement of fluorescence intensity achieved through electro-optical synergy. Fluorophores located sufficiently near silver nanoparticles are combined with diphenylalanine nanotubes (FFNTs) and subjected to a DC electric field. It is proposed that the enhancement of the fluorescence signal arises from the application of the electric field along the length of the FFNTs, which stimulates the pairing of low-energy electrons in the FFNTs with the silver nanoparticles, enabling charge transport across the metal–semiconductor template that enhances the electromagnetic field of the plasmonic nanoparticles. Many-body perturbation theory calculations indicate that, furthermore, the charging of silver may enhance its plasmonic performance intrinsically at particular wavelengths, through band-structure effects. These studies demonstrate for the first time that field-activated plasmonic hybrid platforms can improve fluorescence-based detection beyond using plasmonic nanoparticles alone. In order to widen the use of this hybrid platform, we have applied it to enhance fluorescence from bovine serum albumin and Pseudomonas fluorescens. Significant enhancement in fluorescence intensity was observed from both. The results obtained can provide a reference to be used in the development of biochemical sensors based on surface-enhanced fluorescence.

Multi-spiked silver stars for ultrasensitive and multiplexed SERS detection of analytes

We report a facile synthesis procedure of multi-spiked star-shaped silver structures with sharp morphological features and broad plasmonic absorption for the fabrication of surface-enhanced Raman scattering (SERS) substrates. The multi-branched morphology of silver stars (AgSs) provides copious hot spots on SERS-active substrates to detect ultra-low concentrations of probe molecules. Significant Raman intensity enhancement factors of the order of ∼109 were obtained for the different analytes. The AgSs-based SERS-substrates show ultra-sensitive SERS performance for the detection of probe molecules rhodamine B, methylene blue, thiram, and phosmet with detectabilities 2.6 × 10−16, 1.97 × 10−17, 1.78 × 10−18, and 4.08 × 10−14 M concentration, respectively. The improved SERS sensitivity originated from the additional contribution of chemical enhancement, corroborated by the appearance of new Raman bands in the SERS spectrum. For practical applications, SERS based molecule detection requires high sensitivity, specificity, uniformity, and reproducibility of the SERS signal. We demonstrate the simultaneous detection of multiple analytes, with high specificity, from the complex mixture of molecules with different compositions. The fabricated SERS substrates provide excellent signal uniformity and reproducibility with ∼10% relative standard deviation for the multiple substrates. The real-life application of AgSs-based SERS substrates with the spiked apple juice and ITO-coated PET films without pre-processing is also demonstrated.

Strain mediated light emission using heterojunctions of all-inorganic mixed-halide perovskite nanocrystals via piezo-phototronic effect

Utilizing the superior luminescence properties and high color purity of inorganic perovskite nanocrystals (NCs), we report the fabrication of color-saturated CsPbBr 3−x I x (x = 0–3)/ZnO heterojunctions based white light emitting diodes (LEDs) on a flexible platform. Here, bandgap engineered mixed halide perovskite NCs have been prepared by solution phase synthesis technique that was spin coated on sputtered ZnO film, acting as an electron injector layer as well as an efficient luminescent material. Broad (~ 350–700 nm) electroluminescence (EL) emission features covering the near UV and entire visible region of the electromagnetic spectrum have been successfully achieved at an ambient (humidity ~ 50–55%) condition with comparatively lower forward bias (V th ~ 2 V). Finally, we demonstrate the significant enhancement (up to ~ 75%) of EL intensity by applying an external stress owing to the piezoelectric properties of ZnO films. The modulation of energy band alignment in CsPbBr 3 /ZnO heterojunction due to the local strain induced positive piezo-potential in ZnO leads to an enhanced radiative recombination efficiency in CsPbBr 3 domain, resulting in superior EL emission characteristics. The combinatorial fascinating optical properties of inorganic perovskites and piezo-phototronic effect of ZnO provide a promising platform to fabricate highly luminescent LEDs that may find perspective applications in high-resolution flexible display devices and wearable electronics. • Band gap engineered mixed halide inorganic perovskite NCs (CsPbBr 3−x I x (x = 0–3)) by solution phase synthesis technique. • Perovskite/ZnO p-n junction based moisture resistant broad white LEDs under fairly lower forward bias of ~ 2V. • Successful tuning of EL emission by increasing the I - /Br - ratio of mixed halide perovskites through anion exchange reaction. • Enhancement of EL intensity up to ~ 75% by applying an external stress owing to the piezoelectric properties of ZnO films.

Comparative Analysis of Machine Learning Algorithms on Surface Enhanced Raman Spectra of Clinical Staphylococcus Species.

Raman spectroscopy (RS) is a widely used analytical technique based on the detection of molecular vibrations in a defined system, which generates Raman spectra that contain unique and highly resolved fingerprints of the system. However, the low intensity of normal Raman scattering effect greatly hinders its application. Recently, the newly emerged surface enhanced Raman spectroscopy (SERS) technique overcomes the problem by mixing metal nanoparticles such as gold and silver with samples, which greatly enhances signal intensity of Raman effects by orders of magnitudes when compared with regular RS. In clinical and research laboratories, SERS provides a great potential for fast, sensitive, label-free, and non-destructive microbial detection and identification with the assistance of appropriate machine learning (ML) algorithms. However, choosing an appropriate algorithm for a specific group of bacterial species remains challenging, because with the large volumes of data generated during SERS analysis not all algorithms could achieve a relatively high accuracy. In this study, we compared three unsupervised machine learning methods and 10 supervised machine learning methods, respectively, on 2,752 SERS spectra from 117 Staphylococcus strains belonging to nine clinically important Staphylococcus species in order to test the capacity of different machine learning methods for bacterial rapid differentiation and accurate prediction. According to the results, density-based spatial clustering of applications with noise (DBSCAN) showed the best clustering capacity (Rand index 0.9733) while convolutional neural network (CNN) topped all other supervised machine learning methods as the best model for predicting Staphylococcus species via SERS spectra (ACC 98.21%, AUC 99.93%). Taken together, this study shows that machine learning methods are capable of distinguishing closely related Staphylococcus species and therefore have great application potentials for bacterial pathogen diagnosis in clinical settings.

High sensitivity enhancement of multi-shaped silver-nanoparticle-decorated hydrophilic PVDF-based SERS substrates using solvating pretreatment

We report an extremely sensitive and ultra-low-cost PVDF-based SERS substrate using an easy fabrication process that can be conducted in a laboratory and scaled up for industrial applications. Hydrophilic PVDF membranes were sequentially dipped in ethanol and aqueous sodium chloride solution, following which multi-shaped Ag nanoparticles were deposited on the surface of the membranes by suction filtration. The simple solvating pretreatment led to an approximately 188-fold enhancement in the SERS signal intensity of R6G. Using the hydrophilic PVDF-based SERS substrate, subnanomolar sensitivity for R6G was achieved using 3 μL of sample volume on a 3×3 mm2 SERS substrate within 1 min detection time and without the need for concentration or drying processes. To demonstrate the feasibility of the developed SERS substrate as a sensor for bacterial spore detection, it was applied for the detection of the representative biomarker dipicolinic acid (DPA). The limits of detection of DPA and Bacillus spores were measured as 1 ppm and 5×103 spores/mL, respectively. The optimized configuration of low substrate area and wet micro-analyte volume makes the PVDF-based SERS substrate a simple and low-cost tool for the trace-level detection of small molecules in a rapid, sensitive, and high-throughput manner.

Cyclic Amplification of the Afterglow Luminescent Nanoreporter Enables the Prediction of Anti‐cancer Efficiency

AbstractWe developed a cyclic amplification method for an organic afterglow nanoreporter for the real‐time visualization of self‐generated reactive oxygen species (ROS). We promoted semiconducting polymer nanoparticles (PFODBT) as a candidate for emitting near‐infrared afterglow luminescence. Introduction of a chemiluminescent substrate (CPPO) into PFODBT (PFODBT@CPPO) resulted in a significant enhancement of afterglow intensity through the dual cyclic amplification pathway involving singlet oxygen (1O2). 1O2 produced by PFODBT@CPPO induced cancer cell necrosis and promoted the release of damage‐related molecular patterns, thereby evoking immunogenic cell death (ICD)‐associated immune responses through ROS‐based oxidative stress. The afterglow luminescent signals of the nanoreporter were well correlated with light‐driven 1O2 generation and anti‐cancer efficiency. This imaging strategy provides a non‐invasive tool for predicting the therapeutic outcome that occurs during ROS‐mediated cancer therapy.

Cyclic Amplification of the Afterglow Luminescent Nanoreporter Enables the Prediction of Anti-cancer Efficiency.

We developed a cyclic amplification method for an organic afterglow nanoreporter for the real-time visualization of self-generated reactive oxygen species (ROS). We promoted semiconducting polymer nanoparticles (PFODBT) as a candidate for emitting near-infrared afterglow luminescence. Introduction of a chemiluminescent substrate (CPPO) into PFODBT (PFODBT@CPPO) resulted in a significant enhancement of afterglow intensity through the dual cyclic amplification pathway involving singlet oxygen (1 O2 ). 1 O2 produced by PFODBT@CPPO induced cancer cell necrosis and promoted the release of damage-related molecular patterns, thereby evoking immunogenic cell death (ICD)-associated immune responses through ROS-based oxidative stress. The afterglow luminescent signals of the nanoreporter were well correlated with light-driven 1 O2 generation and anti-cancer efficiency. This imaging strategy provides a non-invasive tool for predicting the therapeutic outcome that occurs during ROS-mediated cancer therapy.

Girl with left-sided hip pain and fever.

A previously healthy 13-year-old girl presented to the pediatric emergency department (PED) with 5 days of progressively worsening left-sided hip pain and 4 days of fever. Although she was able to bear weight on the left leg, she walked with a limp. There was no preceding trauma or illness. In the PED, she was febrile to 39.5°C and tachycardic with other vital signs appropriate for her age. On examination, she had full range of motion of the left hip with significant tenderness only to palpation over the left iliac crest and left gluteal region. Examination was otherwise unremarkable with no overlying skin changes, warmth, edema, or breaks in the skin. Initial laboratory studies revealed abnormalities, including pancytopenia (WBC 2.5 k/uL, hemoglobin 11.5 g/dL, and platelets 32 k/uL), elevated inflammatory markers (C-reactive protein 12.6 mg/dL and erythrocyte sedimentation rate 31 mm/hour), and elevated liver enzymes (alanine aminotransferase 153 U/L and aspartate aminotransferase 221 U/L). The working diagnosis at this point was acute osteomyelitis of the iliac bone. Magnetic resonance imaging (MRI) of the pelvis was performed with and without contrast and revealed abnormal signal intensity and contrast enhancement of the left iliacus and gluteal musculature surrounding the left iliac wing without evidence of abscess (Figure 1). In addition, diffusely increased T2 signal and slightly decreased T1 signal intensity was noted throughout all visible osseous structures (Figure 2). Hours after initial presentation, blood culture resulted positive for methicillin-sensitive staph aureus (MSSA). This patient's MRI findings were consistent with myositis. Given her MSSA bacteremia and imaging finding consistent with soft-tissue infection, the most likely diagnosis is pyomyositis without abscess formation. Acute bacterial myositis can be caused by contiguous spread from a soft-tissue infection, penetrating trauma, or hematogenous spread. When the source is hematogenous, it is referred to as pyomyositis and is often associated with abscess formation. MSSA is the most common pathogen in these cases.1 Although primary pyomyositis is rare in temperate climates, its incidence outside of tropical climates has been increasing in recent years. Risk factors include immunodeficiency (eg, HIV), diabetes mellitus, malignancy, and local muscle trauma. MRI is the imaging modality of choice, and treatment includes drainage of the abscess with pathogen identification when possible, followed by targeted antibiotic therapy.2 This patient's abnormal bone marrow enhancement on MRI and significant cytopenia initially raised suspicion for a malignant process such as leukemic infiltration of the bone marrow. However, given that the patient's cytopenia resolved with antibiotic treatment, bone marrow abnormalities were likely secondary to infection. The patient completed a 3-week course of cephalexin and made a full recovery.

Pulsed high magnetic field-induced reversible blood-brain barrier permeability to enhance brain-targeted drug delivery

ABSTRACT The present study aimed to select an effective Pulsed High Magnetic Field (PHMF) stimulation protocol that would induce the Blood-Brain Barrier’s (BBB) reversible permeability to enhance brain-targeted drug delivery. PHMF was applied to the skull over the right hemisphere of 60 Wistar rats. The sham group contained other 10 rats that did not receive PHMF stimulation. The investigated parameters were repetition frequencies (0.25, 1, and 4 Hz as well as the effective low frequency combined with 10 Hz) and numbers of pulses in each train. Evans Blue Dye (EBD) uptake within the brain parenchyma was measured to select an effective PHMF stimulation protocol. BBB reversibility was evaluated by measuring EBD uptake and Gadobutrol retention, through MRI signal intensity enhancement, within brain parenchyma after exposure to the effective PHMF stimulation protocol at different time points including 0.5, 1, and 24 hours. The obtained results showed that the PHMF stimulation increased the BBB’s reversible permeability; this increase was more significant for 28 pulses with 1 Hz frequency (P < .0001). Changes in EBD uptake and MRI signal intensity in the exposed side (right hemisphere) peaked within 0.5–1 hour and returned to normal levels 24 hours after exposure to the effective protocol of PHMF stimulation (28 pulses with 1 Hz frequency). The Contrast-Enhanced MRI (CE-MRI) signal intensity confirmed the changes in EBD concentration. PHMF stimulation can be used as an effective protocol for enhancing the permeability reversibly of BBB, hence considered a potential clinical approach to brain-targeted drug delivery.

Quenching‐Resistant Solid‐State Photoluminescence of Graphene Quantum Dots: Reduction of π−π Stacking by Surface Functionalization with POSS, PEG, and HDA

AbstractGraphene quantum dots (GQDs) have attracted great attention as next‐generation luminescent nanomaterials due to the advantages of a low‐cost process, low toxicity, and unique photoluminescence (PL). However, in the solid‐state, the strong π−π stacking interactions between the basal planes of GQDs lead to aggregation‐caused PL quenching (ACQ), which impedes practical application to light‐emitting devices. Here, surface functionalized GQDs (F‐GQDs) by polyhedral oligomeric silsesquioxane (POSS), poly(ethylene glycol) (PEG), and hexadecylamine (HDA) to reduce π−π stacking‐induced ACQ is presented. The POSS‐, PEG‐, and HDA‐functionalized GQDs show a significant enhancement in PL intensity compared to bare GQDs by 9.5‐, 9.0‐, and 5.6‐fold in spin‐coated film form and by 8.3‐, 7.2‐, and 3.4‐fold in drop‐casted film form, respectively. Experimental results and molecular dynamics simulations indicate that steric hindrance of the functionalization agent contributes to reducing the π−π stacking between adjacent GQDs and thereby enabling quenching‐resistant PL in the solid‐state. Moreover, the GQD‐based white light‐emitting diodes fabricated by mounting HDA‐GQDs on a UV‐LED chip exhibits efficient down‐conversion for white light emission with a high color rendering index of 86.2 and a correlated‐color temperature of 5612 K at Commission Internationale de l'Éclairage coordinates of (0.333, 0.359).

Monitoring of the decreased mitochondrial viscosity during heat stroke with a mitochondrial AIE probe.

Heat stroke is a fatal condition which usually results in central nervous system dysfunction, organism damage and even death. The relationship between heat stroke and mitochondria is still relatively unknown due to a lack of suitable tools. Herein, an aggregation-induced emission (AIE) probe CSP, by introducing a pyridinium cation as the mitochondria-targeted group to an AIE active core cyanostilbene skeleton, is highly sensitive to viscosity changes due to the restriction of intramolecular motion (RIM) and inhibition of twisted intramolecular charge transfer (TICT) in high-viscosity systems. As expected, with the viscosity increasing from 0.903cP (0% glycerol) to 965cP (99% glycerol), CSP exhibited a significant enhancement (more than 117-fold) in fluorescence intensity at 625nm, with an excellent linear relationship between log I 625 nm and log η (R2 = 0.9869, slope as high as 0.6727). More importantly, using CSP we have successfully monitored the decreased mitochondrial viscosity during heat stroke for the first time. All these features render the probe a promising candidate for further understanding the mechanism underlying mitochondria-associated heat stroke.

Exploitation of the Second Coordination Sphere to Promote Significant Increase of Room-Temperature Luminescence Lifetime and Anion Sensing in Ruthenium–Terpyridine Complexes

This paper deals with the synthesis, characterization, and photophysical behaviors of three Ru(II)-terpyridine complexes derived from a terpyridyl-imidazole ligand (tpy-HImzPh3Me2), wherein a terpyridine moiety has been coupled with a dimethylbenzil unit through a phenylimidazole spacer. The three complexes display strong emission at RT having excited-state lifetimes in the range of 2.3-43.7 ns, depending upon the co-ligand present and the solvents used. Temperature-dependent emission spectral measurements have demonstrated that the energy separation between emitting metal-to-ligand charge transfer state and non-emitting metal-centered state is increased relative to that of [Ru(tpy)2]2+. In contrast to our previously studied Ru(II) complexes containing similar terpyridyl-imidazole motif but differing by peripheral methyl groups, significant enhancement of RT emission intensity and quantum yield and remarkable increase of emission lifetime occur for the present complexes upon protonation of the imidazole nitrogen(s) with perchloric acid. Additionally, by exploiting imidazole NH motif(s), we have examined their anion recognition behaviors in organic and aqueous media. Interestingly, the complexes are capable of visually recognizing cyanide ions in aqueous medium up to the concentration limit of 10-8 M. Computational studies involving density functional theory (DFT) and time-dependent DFT methods have been carried out to obtain insights into their electronic structures and to help with the assignment of absorption and emission bands.

Electric-field induced fluctuations in laser generated plasma plume

The effect of an external electric field on laser-generated plasma has been studied. It is observed that the laser-generated plasma can be used for the ignition of a spark in the presence of a low voltage external electric field. An eight-fold emission intensity enhancement in Cu I spectral lines are measured as compared to the signal intensity in the absence of an external electric field. The plasma parameters remain the same initially, up to a few microseconds after the generation of plasma, and this feature makes it more interesting for the quantitative analysis of any sample using laser induced breakdown spectroscopy (LIBS). In the presence of an external electric field, fluctuations (contraction and expansion) in the laser-generated plasma are observed which increase the plasma decay time and consequently result in enhanced signal intensity.

Enhanced red photoluminescence in chain-like SrAl2O4:Eu3+ nanophosphors: utilizing charge compensation by modulating Na+ co-doping concentration

In the recent days, rare-earth doped phosphors have attracted an immense attraction in luminescence field for various solid-state lighting and electronic display device applications. However, need of efficient red phosphor is a prevalent challenge in this field. Herein, we report a bright red light emitting Na+ co-doped SrAl2O4:Eu3+ phosphor which is synthesized by modified sol–gel technique. These nanophosphors show excellent red emission due to characteristic 5D0 → 7Fj (j = 1, 2, 3, 4) transitions of the doped Eu3+ ions excited by 394 nm. Photoluminescence studies of both Eu3+ doped SrAl2O4 and Na+ co-doped SrAl2O4:Eu3+ has shown more than fourfold increase in the intensity for optimum Na+ addition. The improved decay time obtained from decay measurement has revealed that the co-doped Na+ has successfully reduced the nonradiative transitions. Thus, addition of monovalent Na+ to Eu3+ doped SrAl2O4 was found to be effective to address the charge imbalance problem along with significant enhancement in luminescence intensity and decay time. The results suggest that this nanophosphor could be a major candidate in the rapidly increasing field of solid-state lighting applications.