Increase In Luminescence Intensity Research Articles

Spray pyrolysis synthesis of Sr2Si5N8:Eu2+ nanoparticles for light conversion film enhancing photosynthesis in greenhouses

This study presents a comparative analysis of Sr2Si5N8:Eu2+ nanoparticles synthesized using Spray Pyrolysis (SP) and Solid-State Synthesis (SSS). Through meticulous characterization, we found that the SP method significantly enhanced the morphological and optical properties of the nanoparticles. SP-produced nanoparticles demonstrated a 30% higher crystallinity and a 25% increase in luminescence intensity compared to their SSS counterparts. Additionally, the mesoporous structure characteristic of SP-synthesized particles exhibited a 15% greater surface area, measured at 124.7 m2 g−1, which contributed to improved light absorption capabilities. These attributes are crucial for the intended application of enhancing photosynthesis in greenhouse environments. The UV–Visible spectra confirmed that SP nanoparticles possess superior light conversion capabilities, with notable implications for optimizing light distribution to facilitate plant growth. This research highlighted the advantages of SP, including ease of scalability and enhanced optical performance, which are pivotal for agricultural applications. The study emphasized that the choice of synthesis method played a critical role in tailoring the properties of Sr2Si5N8:Eu2+ nanoparticles for specific functional requirements in optical and agricultural technologies.

Tandem Four-Component Reaction to Access Fused Polycycles Exhibiting Aggregation-Enhanced Through-Space Charge Transfer Emission.

Rapid construction of new fluorescence emitters is essential in advancing synthetic luminescent materials. This study illustrated a piperidine-promoted reaction of chiral dialdehyde with benzoylacetonitrile and malonitrile, leading to the formation of the 6/6/7 fused cyclic product in good yield. The proposed reaction mechanism involves a dual condensation/cyclization process, achieving the formation of up to six bonds for fused polycycles. The single crystal structure analysis revealed that the fused cyclic skeleton contains face-to-face naphthyl and cyanoalkenyl motifs, which act as the electronic donor and acceptor, respectively, potentially resulting in through-space charge transfer (TSCT) emission. While the TSCT emissions were weak in solution, a notable increase in luminescence intensity was observed upon aggregation, indicating bright fluorescent light. A series of theoretical analyses further supported the possibility of spatial electronic communication based on frontier molecular orbitals, the distance of charge transfer, and reduced density gradient analysis. This work not only provides guidance for the one-step synthesis of complex polycycles, but also offers valuable insights into the design of aggregation-enhanced TSCT emission materials.

Effect of Post-Implantation Heat Treatment Conditions on Photoluminescent Properties of Ion-Synthesized Gallium Oxide Nanocrystals.

A novel and promising way for creating nanomaterials based on gallium oxide is the ion synthesis of Ga2O3 nanocrystals in a SiO2/Si dielectric matrix. The properties of nanocrystals are determined by the conditions of ion synthesis-the parameters of ion irradiation and post-implantation heat treatment. In this work, the light-emitting properties of Ga2O3 nanocrystals were studied depending on the temperature and annealing atmosphere. It was found that annealing at a temperature of 900 °C leads to the appearance of intense luminescence with a maximum at ~480 nm caused by the recombination of donor-acceptor pairs. An increase in luminescence intensity upon annealing in an oxidizing atmosphere is shown. Based on data from photoluminescence excitation spectroscopy and high-resolution transmission electron microscopy, a hypothesis about the possibility of the participation of a quantum-size effect during radiative recombination is proposed. A mechanism for the formation of Ga2O3 nanocrystals during ion synthesis is suggested, which makes it possible to describe the change in the luminescent properties of the synthesized samples with varying conditions of post-implantation heat treatment.

Colour tuning in Sm3+ activated and Sm3+/Eu3+ co-activated SrBi4Ti4O15 phosphors for w-LED applications

SrBi4Ti4O15 (SBT) phosphors activated by Sm3+ and co-activated by Eu3+ have been synthesized in the current research using a straightforward solid-state reaction technique. X-ray Diffraction (XRD) confirms the sample's crystallinity. Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and elemental mapping have been used to analyse the morphology and elemental composition of the synthesized phosphor. Fourier-transform infrared spectroscopy (FT-IR) analysis has confirmed the vibrational characteristics of the as prepared phosphor. Photoluminescence studies show increase in luminescence intensity in case of Sm3+/Eu3+ co-activated phosphors as compared with singly doped Eu3+ and Sm3+ activated SBTO phosphors. Colour tunability was also observed from reddish-orange to pure red region when Sm3+ activated phosphors were co-activated with Eu3+ ions. These outcomes demonstrate that SrBi4Ti4O15 phosphors activated or co-activated with Sm3+ and Eu3+ can be deployed in w-LEDs and other display devices applications.

Structural, Optical, and Electronic Properties of Epitaxial β‐(AlxGa1‐x)2O3 Films for Optoelectronic Devices

AbstractBandgap engineering in monoclinic gallium oxide (β‐Ga2O3) is a powerful strategy for designing semiconductor optoelectronic devices with specific functionalities. In this work, aluminum doping is utilized to modulate the bandgap of Ga2O3. By growing epitaxial β‐(AlxGa1‐x)2O3 (0≤ x≤ 0.84) films on c‐plane sapphire substrates using RF magnetron sputtering, it allowed to tune the energy bandgap, achieving values as high as 6.10 eV. The increased luminescence intensity is attributed to the recombination between donor and acceptor transitions induced by Al doping, resulting in more defects. Additionally, the luminescent band experienced blueshifts due to the enhanced bandgaps. Moreover, density of functional theory (DFT) simulations confirmed the sensitivity of the bandgap to Al content, distinguishing between Ga‐dominated (x < 0.5) and Al‐dominated (x > 0.5) β‐(AlxGa1‐x)2O3. Notably, the bandgap increased more rapidly in Ga‐dominated structures compared to Al‐dominated ones. The electronic structure analysis revealed a redistribution of Ga d states from valence to conduction bands, attributed to the introduction of numerous Al p states. These combined experimental and detailed electronic structure investigations proved crucial insights for designing the structure and exploring potential applications of β‐(AlxGa1‐x)2O3 in photonic devices.

Laser-induced changes on the upconversion luminescence properties of BiF3:Yb,Er nanoparticles

BiF3 nanoparticles doped with Yb3+ and Er3+ ions in varying ratios were prepared by co-precipitation method and its upconversion luminescence (UCL) properties were investigated in detail before and after high-intensity laser treatment. Green-to-red ratio (GRR) of luminescence from cubic-BiF3:Yb,Er nanoparticles is found to increase with an increase in laser power for as prepared sample. Unlike this, for conventional Yb,Er doped upconversion nanoparticles (UCNPs) such as cubic NaYF4:Yb,Er and hexagonal-NaYF4:Yb,Er, a decrease in GRR values is observed with an increase in laser power. This has been explained based on the reduced extent of Er3+-Er3+ interaction in BiF3:Yb,Er nanoparticles compared to that existing in cubic and hexagonal forms of NaYF4:Yb,Er, nanoparticles. Reduced interaction is brought about by higher lattice parameter of BiF3 host compared to the NaYF4 host which leads to a lesser extent of cross-relaxation in the former host thereby favoring the population of 4S3/2 and 2H11/2 levels of Er3+. Effect of high-intensity laser (180W/cm2) irradiation on BiF3:Yb,Er nanoparticles resulted in an irreversible five-fold increase in upconversion luminescence intensity and this is attributed to combined effect of partial conversion of BiF3 to cubic Bi2O3 and removal of adsorbed water molecules. These inferences are confirmed by XRD and TEM measurements carried out on laser-treated sample. Improved luminescence intensity from the laser-treated sample is also confirmed by the high-contrast clear images obtained from impressions made using high-intensity laser irradiation on BiF3:Yb,Er nanoparticles. BiF3:Yb,Er nanoparticles showed an excellent thermal sensitivity of 0.3% K−1 at room temperature and the value is comparable with that of conventional β-NaYF4:Yb,Er nanoparticles.

Development of pH‐Sensitive Film for Detection of Implant Infection via Ultrasound Luminescent Chemical Imaging

AbstractA new hybrid ultrasound luminescent chemical imaging technique is described along with a pH sensor to image chemical concentrations at the surface of implanted medical devices. The purpose is to detect and study local biochemistry during infection. The sensor comprises a mechanoluminescent film (SrAl2O4:Eu, Dy microphosphors embedded in a biocompatible polymer film) and a pH indicator dye. A focused ultrasound beam generates green luminescence at the ultrasound focal point. By pulsing the ultrasound ON and OFF, the modulated luminescence can be distinguished from persistent luminescence, for high spatial resolution imaging. A red fluorescent dye and the pH indicator dye bromothymol blue are added to the coating to modulate the red‐light transmittance via pH dependent absorbance. Acidosis is observed as an increase in red luminescence intensity in spectroscopy and imaging. The films are sensitive to biologically relevant changes in pH (6.0–8.0) and can be imaged through optically scattering media to mimic tissue. The images have a knife edge spatial resolution of ≈3 mm through optically scattering phantoms, limited by the focused ultrasound spot size. This novel technique may permit the elucidation of implant infection at the implant surface and can be further developed for the measurement of other relevant chemical species in the future.

Study on the pathway of performance improvement and mechanism of Gd2O2S:Tb3+ green phosphor

To improve the luminescence performance of Gd2O2S:Tb3+, Gd2O2S:Tb3+, Tm3+, Gd2O2S:Tb3+, Dy3+, Tm3+ and Gd2O2S:Tb3+, Dy3+, Tm3+@SiO2 phosphors have been prepared by molten salt method. The samples are characterized using XRD, SEM, TEM, FT-IR, UV-Vis absorption spectroscopy, photoluminescence, cathodoluminescence and thermal stabilization tests. XRD tests and refinement results show that the crystal structure of the phosphor is still the hexagonal Gd2O2S crystalline phase and the lattice parameter decrease due to Dy3+/Tm3+ occupying the Gd3+ sites. SEM images and mapping of each element show that the particle grain and all expected elements distribute uniformly. TEM results illustrate that SiO2 coating is in an amorphous form on the surface of the powder grains. FT-IR tests indicate that SiO2 is present on the powder surface through Si-O-Gd bonding. The results of photoluminescence and cathodoluminescence show that the luminescence intensity increase 50% while adding Tm3+ into Gd2O2S:Tb3+, Gd2O2S:Tb3+, Dy3+ phosphors caused mainly by the energy transfer from Dy3+/Tm3+ to Tb3+. The core-shell structure of Gd2O2S:Tb3+, Dy3+, Tm3+@SiO2 has better photoluminescence and cathodoluminescence and the fluorescence lifetime remains unchanged while SiO2 coats phosphor. And it has good thermal stability. Its luminescence intensity at 425 K reaches 71.4% of that at room temperature, which is better than the corresponding value (46.4%) for the uncoated sample.

Metal Organic Vapor‐Phase Epitaxy Growth of Multilayer Stacked InAsSb/InAsP Superlattices on GaAs and InAs Substrate

Midinfrared photonic devices are used as lasers and photodetectors in optical gas sensors and fiber‐optic communications. Herein, the pair number dependence and strain compensation dependence of the InAsSb/InAsP superlattice structure to increase luminescence intensity and reduce crystal defects is investigated. InAs substrates are used to demonstrate various effects of strain compensation, including its role in increasing luminescence intensity and improving the surface flatness. Furthermore, the photoluminescence spectra of a grown superlattice between the InAs substrate and GaAs substrate with two‐temperature‐step growth are shown.

Effect of Sintering Time and Cl Doping Concentrations on Structural, Optical, and Luminescence Properties of ZnO Nanoparticles

Zinc oxide (ZnO) nanoparticles were synthesized hydrothermally using zinc acetate dihydrate and sodium thiosulfate pentahydrate precursors. The synthesized powders were sintered in air at 600 °C for different durations with a Cl-doping concentration of 25 mg/g. The optimal sintering time was found to be 5 h, resulting in the successful formation of the ZnO phase with small particle sizes of around 90 nm, nominal atomic fractions of Zn and O (~50%, ~50%), and increased luminescence intensity. The ideal concentration of Cl was discovered to be 25 mg/g of ZnO, which resulted in the highest luminescence intensity. The ZnO luminescence characteristics were observed in emission bands peaking at approximately 503 nm attributed to the transition from oxygen vacancies. A considerable improvement in the emission intensity was observed with increased Cl doping concentration, up to eight orders of magnitude, compared to pristine ZnO nanoparticles. However, the luminescence intensity decreased in samples with higher concentrations of Cl doping due to concentration quenching. These preliminary outcomes suggest that Cl-doped ZnO nanoparticles could be used for radiation detector development for radon monitoring and other related applications.

Spectral Tunability, Luminescence Enhancement, and Temperature Sensitivity of Sb3+-Doped Bismuth-Based Halide Emission Crystals for Anti-Counterfeiting Applications.

The synthesis of sustainable luminescent materials with simplicity, low energy consumption, and nontoxicity is of great importance in the field of chemistry and materials science. In this study, a room temperature evaporation method was employed to synthesize Sb3+-doped bismuth-based halide emission crystals, allowing for investigation of spectral tuning, luminescence enhancement, and temperature sensitivity. By substitution of Rb+ with varying concentrations of Cs+ in Rb3BiCl6 (RBC), the luminescent color of the crystals can be tuned from orange to yellow. The resulting alloyed yellow-emitting crystals were identified as Rb2CsBiCl6 (RCBC). Remarkably, when one-third of the Rb+ ions were replaced by Cs+ in the RBC, the crystals exhibited improved thermal stability and a 20-fold increase in luminescence intensity. The temperature-sensitive behavior was observed for RBC:Sb, with emission shifting from 590 to 574 nm upon heating while the yellow emission of RCBC:Sb exhibited no significant peak shift with temperature. Notably, the yellow emission of RBC:Sb could be reversibly converted back to orange light upon cooling to room temperature. In contrast, RCBC:Sb exhibited no significant peak shift with temperature. The differential temperature sensitivity between RBC:Sb and RCBC:Sb offers potential applications in anti-counterfeiting measures.

X-ray structure, chelation enhanced fluorescence effect, thermal and redox properties of a new europium(III) complex based on bioactive naphthoquinone

The synthesis of metal complexes containing natural naphthoquinones has been highlighted due to their interesting electrochemical and spectroscopic properties, which may have a primordial influence on their pharmacological bioactivities. Simultaneously, processes of interaction of lanthanoid ions with organic ligands indicate the formation of coordination compounds that have marked luminescent properties of technological and medical diagnostic interest. Thus, this work describes the synthesis, characterization, and study of the properties of a new lawsone-EuIII metal complex, including the structural determination by XRD and the thermal, redox, and luminescent properties. The nine-coordinated complex exhibits a tri-hooded trigonal prismatic geometry, in which the metal ion is bound to nine oxygen atoms from three lawsone molecules and three water molecules, and the molecular structure still has approximately four water molecules as solvates, thus constituting [EuIII(C10H5O3)3(H2O)3].4H2O (FW = 797.49 g mol−1). The average CO and CC bond lengths indicate that naphthoquinone is coordinated in its anionic form, while the structural conformation shows intermolecular hydrogen interactions, which form interesting water channels. Thermal analyzes provided information regarding the decomposition behavior of the compound and its thermodynamic stability involving endothermic and exothermic processes. Electrochemical studies of the complex show that the processes associated with the ligand are shifted, with concomitant reduction of the Eu3+ ion. This new rearrangement is also responsible for differences in electronic transitions, such as the effect of increasing luminescence intensity (CHEF effect), and the phenomenon occurs through the antenna-like intramolecular interaction of the lawsonate anion with the europium(III) ion.

Synthesis of a lanthanide-based bimetallic-metal-organic framework for luminescence sensing anthrax biomarker

Lanthanide luminescence sensors have attracted extensive attention in the detection of 2, 6-pyridinedicarboxylic acid (DPA), the main biomarker of anthrax. In previous reports detecting DPA, luminescence probes may not have high selectivity and high specificity for identification. In the present study, a highly specific and sensitive luminescence probe was synthesized. In this paper, [TbxGd1-x (PBA)2NO3·2H2O]n is synthesized by solvothermal method using HPBA = 3.5-bis(triazol-1-yl)benzoic acid and Ln (NO3)3·6H2O (Ln = Tb, Gd). Through modulating the molar ratio of Tb3+ ions and Gd3+ ions, the distance between Ln3+ ions is changed, leading to a change in the energy transfer from the ligand to Tb3+, which in turn leads to an increase in luminescence intensity. Meanwhile the luminous colour is regulated by the ratio of Tb/Gd, which changes from green to white as the Gd ion gradually increases. The bimetallic ratiometric luminescence sensor realized accurate, high sensitivity (LOD is 1.03 × 10−6 M) and high selectivity detection of DPA. Due to the simple synthesis method and low technical requirements, this work provides a good strategy for the development of simple and effective bimetallic ratiometric luminescence sensors.

Quantum-Chemical Study of Aggregation of 5-(4'-Dimethylaminobenzylidene)Barbituric Acid

Decreasing fluorescence efficiency in the solid-state is general and is mainly attributed to the intermolecular vibronic interactions, which induce the nonradiative deactivation process. Whereas the isolated dye molecules are virtually non-luminescent in dilute solutions, they become highly emissive upon solution thickening or aggregation in poor solvents or in the solid-state show an increase of luminescence intensity, the phenomenon of the aggregation-induced emission (AIE phenomenon). The development of efficient luminescent materials is a topic of great current interest. Theoretical calculation shows that the dye molecules' aggregation-induced emission characteristics result from intermolecular interactions. Utilizing such features, the molecules can be employed as fluorescent probes for the detection of the ethanol content in aqueous solutions. Quantum-chemical calculations using the method of density functional theory the computations of structure and electronic spectra of aggregated forms of 5-(4’-dimethylaminobenzylidene)barbituric acid and the Gaussian 98 program packages have been performed. The unusual spectral behavior of 5-(4’-dimethylamino-benzylidene)barbituric acid was investigated theoretically by the DFT method and its time-dependent variant TDDFT. Carried out calculations using Zindo, as well as ab initio calculations, confirm the appearance of a new band during aggregation and its shift to the red region when the number of molecules increases.

LUMINESCENT PROPERTIES OF Nd(III) COMPLEXES WITH ETHY­LENE­DIAMINE-N,N'-DISUCCINIC AND N,N-BIS(PHOSPHONO­METHYL)-2-AMINOPROPIONIC ACIDS

An analysis of the fluorescent characteristics of ethylenediamine-N,N'-disuccinic and N,N-bis(phosphonomethyl)-2-aminopropionic acids was carried out depending on the pH of the solutions. It was established that the change in fluorescence intensity and lifetime is associated with the formation of variously protonated forms of acids in which stable H-cycles are formed with the participation of hydrogen bonds. The energies of the singlet and triplet levels of the ligands were experimentally determined, the values of which are higher than the energy of the radiative level of the Nd(III) ion, which indicates the possibility of intramolecular transfer of the excitation energy to the resonance level of the lanthanide ion. It was established that both homo- and heteronuclear complexes of Nd(III) exhibit 4f-luminescence in the near-IR region. It was found that for phosphorus-containing complexes there is an increase in luminescence intensity and relative quantum yields in comparison with aminocarboxylate analogs. In heterometallic complexes based on aminopolycarboxylic acids, the intramolecular transfer of energy from the excited level of Co(II) to the resonance level of the f-metal leads to sensitization of the 4f-luminescence of the neodymium ion.

Effect of amphiphilic polymers and sodium alginate on the activity of methylene blue in photogeneration of singlet oxygen 1О2

The influence of amphiphilic polymers (APs): poly-N-vinylpyrrolidone, polyethylene glycol and pluronics F127, F108, as well as sodium alginate (SA) on the activity of methylene blue (MB) in the photogeneration of singlet oxygen 1О2, specifically, in a model photooxidation reaction of tryptophan in water was studied. It was shown that in the presence of all the above-mentioned AP, an increase in the effective rate constant (k eff) of tryptophan photooxidation is observed. It was suggested that the observed effect is associated with the interaction of MB with APs, which leads to disaggregation of dye associates. Such disaggregation leads to an increase in the optical density and intensity of MB luminescence. It was also shown that the photocatalytic activity of MB decreases by a factor of 1.5–3.5 in the presence of SA, which is due to the ionic interaction of the cationic MB with polyanionic SA. The interaction of MB with polysaccharide is confirmed by changes in the absorption and fluorescence spectra of the dye. The introduction of APs into a solution containing MB and SA prevents the interaction between MB and polysaccharide, which leads to an increase in the k eff values of tryptophan photooxidation in the presence of MB-AP-SA system, as well as to an increase in the optical density and fluorescence intensity of MB when AP and SA are added. The existence of weak interactions between the hydrophobic groups of MB molecules and the AP (polyvinylpyrrolidone) is also evidenced by the data obtained through 1H-NMR spectroscopy and the degree of MB fluorescence anisotropy. The AFM method shows the change in the surface structure of a thin film obtained by evaporating an aqueous solution of MB-F108-SA compared to the corresponding structure of a film obtained by evaporating an aqueous solution of MB-SA. MB-AP and MB-AP-SA systems may be promising for practical application in the aPDT treatment of chronic microbial superficial infections.

Hydrogen iodide (HI) neutral beam etching characteristics of InGaN and GaN for micro-LED fabrication

We investigated the etching characteristics of hydrogen iodide (HI) neutral beam etching (NBE) of GaN and InGaN and compared with Cl2 NBE. We showed the advantages of HI NBE versus Cl2 NBE, namely: higher InGaN etch rate, better surface smoothness, and significantly reduced etching residues. Moreover, HI NBE was suppressed of yellow luminescence compared with Cl2 plasma. InCl x is a product of Cl2 NBE. It does not evaporate and remains on the surface as a residue, resulting in a low InGaN etching rate. We found that HI NBE has a higher reactivity with In resulting in InGaN etch rates up to 6.3 nm min−1, and low activation energy for InGaN of approximately 0.015 eV, and a thinner reaction layer than Cl2 NBE due to high volatility of In-I compounds. HI NBE resulted in smoother etching surface with a root mean square average (rms) of 2.9 nm of HI NBE than Cl2 NBE (rms: 4.3 nm) with controlled etching residue. Moreover, the defect generation was suppressed in HI NBE compared to Cl2 plasma, as indicated by lower yellow luminescence intensity increase after etching. Therefore, HI NBE is potentially useful for high throughput fabrication of μLEDs.

Adjustment of Bi3+ Luminescence and Thermal Quenching Properties by B'-Site Ion Substitution Strategy in Double Perovskite CaLaMgSb/TaO6:Bi3+ Phosphor.

Thermal quenching has always been one of the most difficult issues in creating high-quality phosphor conversion light-emitting diodes (pc-LED), and a family of strategies are urgently needed to improve the luminescence performance of phosphors at high temperatures. In this contribution, a novel B'-site substitution CaLaMgSbxTa1-xO6:Bi3+ phosphor was constructed using an ion substitution strategy in the matrix with a green activator Bi3+ and a novel double perovskite material. When Sb5+ replaces Ta5+, a surprising increase in luminescence intensity occurs and the thermal quenching properties are greatly improved. The shift of the Raman characteristic peak to a smaller wavenumber and the reduction of the Bi-O bond length confirm that the crystal field environment around Bi3+ changes, which has a substantial effect on the crystal field splitting and nepheline effect of Bi3+ ions, affecting the crystal field splitting energy (Dq). This results in a corresponding increase of the band gap and the thermal quenching activation energy (ΔE) of the activator Bi3+. From the perspective of Dq, the intrinsic relationships among the activator ion band gap, bond length, and Raman characteristic peak changes were analyzed, and a mechanism for regulating luminescence thermal quenching properties was constructed, which provides an effective strategy for improving the promising new materials such as double perovskite.

Competitive ELISA based on pH-responsive persistent luminescence nanoparticles for autofluorescence-free biosensor determination of ochratoxin A in cereals.

An accurate and sensitive competitive enzyme-linked immunosorbent assay (ELISA) based on persistent luminescence nanoparticles Zn2GeO4:Mn2+, Eu3+ (ZGME) was developed for detecting ochratoxin A (OTA), a powerfully toxic mycotoxin usually found in grains. As a signal output element of autofluorescence-free biosensors, ZGME can be integrated into ELISA with glucose oxidase (GOx)-binding OTA molecules due to its excellent pH-responsive persistent luminescence. In the absence of OTA, the OTA-GOx conjugate was captured by the anti-OTA monoclonal antibody (anti-OTA mAb) pre-coated on the 96-well plate. The results indicate a decrease in the pH value of the solution, which triggered the quenching of ZGME luminescence due to GOx-dependent gluconic acid production. The presence of OTA inhibited the binding of OTA-GOx on the plate, thus decreasing the production of gluconic acid and increasing the persistent luminous intensity of ZGME. Under the optimized concentrations of anti-OTA mAb and OTA-GOx, quantitative determination of OTA was achieved by plotting the increase or decrease in persistent luminescence intensity of ZGME at 535nm. In this study, the linear range was from 0.1μg L-1 to 63μg L-1, and the limit of detection (LOD) was as low as 0.045μg L-1. In five food samples (corn grit, brown rice, soybean, rice, and wheat), the results exhibited good stability and repeatability, with a recovery range from 81.3% to 94.4% and a relative standard deviation (RSD) of less than 4.2%. Hence, the established method provides a sensitive, accurate, and autofluorescence-free approach for the determination of OTA in different grain samples.

Characterization of pulsed laser deposited La2O2S:Eu3+ thin films and effect of coating with graphene oxide layers

Surface coatings have been widely used to improve phosphor characteristics for the purpose of increasing luminescence intensity and protecting against degradation. In this study, an uncoated La2O2S:Eu3+ thin film is compared to films coated by graphene oxide, as prepared or annealed in an inert or reducing atmosphere. The characteristic red emission of Eu3+ ions was observed for all samples and attributed to 5D0-7F2 transitions, while no luminescence associated with graphene oxide was observed. The luminescence intensity from the as-coated sample and the one annealed in an inert Ar atmosphere was less, compared to the uncoated film, whereas the coated sample annealed in a reducing atmosphere (Ar/H2) had emission, which was of similar intensity to the uncoated sample. Its degradation, and that of the uncoated sample, were studied by recording Auger electron spectroscopy and cathodoluminescence measurements, simultaneously. During electron irradiation, the surface of the uncoated sample was converted to a much more luminescent layer as C and S were gradually removed from the surface. Auger electron spectroscopy measurements of the coated sample showed that even initially, it had almost no S on the surface. The loss of S was attributed to annealing in Ar/H2, where H2S gas may be produced as the phosphor was converted into La2O3. This La2O3 subsequently formed La(OH)3 due to its hydroscopic nature. Unlike the uncoated sample, from which C due to unintentional contamination was fairly easily removed from the surface, C on the surface of the coated sample became less but was resistant to removal, which was associated with the formation of CHLaO3 at the surface as suggested by x-ray diffraction. Although coating with graphene oxide did not result in chemically stable La2O2S:Eu3+ thin films, the cathodoluminescence intensity of both the uncoated and graphene oxide coated samples annealed in reducing atmosphere increased during electron beam exposure (with no change in the form of the emission spectra) so that such films may have potential cathodoluminescence applications.