Investigation of the influence of silver and tin on the luminescence of trivalent europium ions in glass

Europium-doped aluminophosphate glasses prepared by the melt-quenching technique have been studied by photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). The effects of silver and tin doping, and of further thermal processing on Eu³⁺ ions luminescence have been assessed. For the glass system containing only europium, Eu³⁺ PL observed under UV excitation is suggested to occur through energy transfer from the excited glass host. After silver and tin doping, an enhanced UV excited Eu³⁺ PL has been indicated to occur essentially due to radiative energy transfer from isolated Ag⁺ ions and/or two fold-coordinated Sn centers. Since thermal processing of the material leads to a quenching effect on Eu³⁺ PL and Ag nanoparticles (NPs) formation due to reduction of silver ions by tin, XPS was employed in order to investigate the possibility for Eu³⁺→Eu²⁺ reduction during HT as a potential source of the PL decrease. The data points towards Ag NPs as main responsible for the observed weakening of Eu³⁺ PL.     

Ag+掺杂的立方相Y2O3:Eu纳米晶体粉末发光强度研究

采用化学自燃烧法制备了不同Ag⁺掺杂浓度的Y₂O₃:Eu纳米晶体粉末样品(［Y³⁺］∶［Eu³⁺］∶［Ag⁺］=99∶1∶X，X=0—3.5×10^-2)，以及通过退火处理得到了相应的体材料.根据X射线衍射谱确定所得纳米和体材料样品均为纯立方相.实验表明在纳米尺寸样品中随着Ag离子浓度的增加，荧光发射强度随之增加，当X=2×10^-2时达到最大值，其发光强度比X=0时提高了近50%.当Ag离子浓度继续增加，样品发光强度保持不变.在相应的体材料样品中则没有观察到此现象.通过对各样品的发射光谱，激发光谱，X射线衍射图谱，透射电镜(TEM)照片和荧光衰减曲线的研究，分析了引起纳米样品荧光强度变化的原因是由于Ag离子与表面悬键氧结合，从而使这一无辐射通道阻断，使发光中心Eu³⁺的量子效率提高；Ag⁺的引入所带来的另一个效应是使激发更为有效.这两方面原因使发光效率得到了提高.     

A FRET Fluorescent Sensor for Ratiometric and Visual Detection of Sulfide Based on Carbon Dots and Silver Nanoclusters

In this work, the fluorescent sensor based on fluorescence resonance energy transfer (FRET) and electrostatic interaction (EI) was prepared for the ratiometric and visual detecting S^2–. The FRET fluorescent sensor consists of two fluorophores, with carbon dots (CDs) as energy donors and silver nanoclusters (Ag NCs) as acceptors. At 390 nm excitation, CDs and Ag NCs showed two well-separated peaks at 445 nm and 660 nm, separately. The existence of S^2– caused the red fluorescence at 660 nm to be quenched, whereas the blue fluorescence at 445 nm was restored, and the fluorescence color of the ratiometric sensor changed from pink to blue. It could be employed in ratiometric and visual detecting S^2–. The linear range of quantitative detection S^2– was 0.5–100 μM, and its detection limit was 0.35 μM. CDs-Ag NCs could be used for detecting S^2– in mineral water and tap water. The results showed that the FRET ratiometric fluorescent sensor exhibits good anti-interference and high selectivity for detecting S^2– in environmental water samples.

     

A Novel Fluorescent Biosensor for Detection of Silver Ions Based on Upconversion Nanoparticles

In this paper, we report a simple and sensitive fluorescent biosensor for the quantitative analysis of silver ions (Ag⁺) by using NaYF₄:Yb³⁺, Tm³⁺ upconversion nanoparticles (UCNPs). Ag⁺ could oxidize o-phenylenediamine (OPD) to the oxidized OPD (oxOPD) directly. The fluorescence of UCNPs can be significantly quenched by oxOPD through inner filter effects (IFE). Under the optimized conditions, the Ag⁺ concentration is proportional to the changes of the fluorescence intensity of UCNPs. The proposed method shows high selectivity and Ag⁺ could be quantitatively detected in the range of 0 to 0.5 mM with a low detection limit of 33 nM for Ag⁺. The selectivity and sensitivity of the detection can also be satisfactory. More importantly, this method has potential in practical application to detect Ag⁺ in real samples without interference.     

A Novel Ratiometric Fluorescent Chemosensor for Cd2+

Novel ratiometric fluorescent chemosensor C7 was synthesized and characterized by UV–vis and fluorescence spectroscopy. C7 showed high sensitivity for Cd²⁺ among Na⁺, Mg²⁺, Cu²⁺, Pb²⁺, Ni²⁺, Fe³⁺, Zn²⁺, Ag⁺ Hg²⁺ and Cd²⁺ in ethanol.     

One-pot synthesis of carbon dots co-doped with N and S: high quantum yield governed by molecular state and fluorescence detection of Ag+

Fluorescent carbon-based nanoparticles, called chronically as carbon dots (CDs), were synthesised from citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method. After a series of micro-structural characterisation, N and S elements could be sufficiently doped by means of the heteroatom in the CDs solution. The as-prepared CDs solution showed blue colour fluorescence with the highest QY of 78.6%, and study on the UV–visible and PL spectra further revealed that the outstanding fluorescence of as-prepared CDs mainly originates from the generated molecular fluorophores instead of the surface state. Owing to the strong fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag⁺ with high sensitivity and selectivity. However, the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH₂ groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag⁺ ions, which promises a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.

This figure shows citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method to prepare CDs with blue colour fluorescence and the highest QY of 78.6%. Owing to the excellent fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag⁺ with high sensitivity and selectivity, and the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH₂ groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag⁺ ions, which promises a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.     

A Label-Free Oligonucleotide Based Thioflavin-T Fluorescent Switch for Ag<Superscript>+</Superscript> Detection with low Background Emission

A novel fluorescent Ag⁺ sensor was developed based on the label-free silver (I) specific oligonucleotide (SSO) and Thioflavine T (ThT) monomer-excimer switch. C-rich SSO which contain C-C mismatched base pairs can selectively bind to Ag⁺ ions and the formed duplexes which constructed by C-Ag⁺-C structure are thermally stabilized without largely altering the double helical structure. ThT give very weak fluorescent in bulk solution and/or in the presence of SSO. However ThT shows high fluorescence in the presence of SSO and Ag⁺ at the same time mainly because ThT excimer, which has the high quantum yield, formed and stabilized in the minor or major groove. Based on the discovery, we developed the novel Ag⁺ sensor. Under the optimum condition, the selectivity of this system for Ag⁺ over other metal ions in aqueous solution is remarkably high, and Ag⁺ can be quantified over the dynamic range of 30–450 nM, with a limit of detection of ~16 nM and a linear correlation coefficient of 0.995.     

Enhanced UV-excited luminescence of europium ions in silver/tin-doped glass

Glasses containing silver, tin and europium were prepared by the melt-quenching technique with silver nanoparticles (NPs) being embedded upon heat treatment (HT). An intensification of Eu³⁺ ions emission was observed for non-resonant excitation around 270 nm, corresponding to UV absorption in the material. Optical measurements suggest that light absorption occurs at single Ag⁺ ions and/or twofold-coordinated Sn centers followed by energy transfer to europium which results in populating the ⁵D₀ emitting state in Eu³⁺. After HT at 843 K, a quenching effect is observed on Eu³⁺ luminescence with increasing holding time in the 350–550 nm excitation range. The quenching effect shows with the presence of Ag NPs which may provide multipole radiationless pathways for excitation energy loss in europium ions.     

Luminescence of CdS:Ag Quantum Dots in a Polymethacrylate Matrix

Semiconductor quantum dots (QDs) exhibit intense luminescence and reproduce optical characteristics. Doping with metal ions has a positive effect on their properties. Introduction of QDs into polymer matrices leads to the formation of a required morphology of composites. There is a problem in synthesis of optically transparent polymer composites containing QDs of the А²В⁶ group that consists in the extremely low solubility of metal chalcogenides and most of their precursors in monomers. To solve this problem, we used colloidal synthesis. CdS QDs were synthesized by the method of appearing reagents in situ in methylmethacrylate (MMA). Doping with Ag⁺ ions was performed by adding a silver salt into the reaction mixture during the synthesis of CdS QDs. The PMMA/CdS:Ag luminescent polymer glasses were synthesized by radical block polymerization of MMA. The transparency of the composites at wavelengths exceeding 500 nm reaches 92% (5 mm). The luminescence excitation is related to the interband electron transitions in CdS crystals. Luminescence in the range of 500–600 nm is observed due to electron relaxation via a system of levels in the band gap of doped CdS crystals. The positions and intensities of the spectral bands depend on the Ag⁺ concentration, particle size, excitation wavelength, and other factors. The formation of Cd(Ag)S/Ag₂S structures at Ag⁺ concentrations higher than 5.0 × 10^–3 mol/L quenches the luminescence.     

Synthesis of Pyridine-Based 1,3,4-Oxadiazole Derivative as Fluorescence Turn-On Sensor for High Selectivity of Ag+

An oxadiazole derivative(OXD) containing symmetrical pyridine-2-formamidophenyl-binded moiety was synthesised as fluorescence turn-on sensor OA1. Its ultraviolet–visible(UV–vis) and fluorescent spectra(FS) gave prominent fluorescence enhancement only for monovalent silver ion(Ag⁺) in HEPES buffer solution (10 mM, pH?=?7.0, DMF-H₂O, 9:1, v/v), which indicated the photo-induced electron transfer(PET) occurred from the donor of pyridine-2-formamidophenyl group to oxadiazole fluorophore. The present study demonstrated that OA1 was a viable candidate as fluorescent receptor for a new Ag⁺ sensor. And the results of fluorescent spectral titration showed this sensor formed 1:1 complex with Ag⁺.     

Förster resonance energy transfer in hybrid associates of colloidal Ag<Subscript>2</Subscript>S quantum dots with thionine molecules

Nonradiative resonance energy transfer in hydrophilic hybrid associates of thionine molecules (TH⁺) with colloidal Ag₂S quantum dots (QDs) with average diameter of 3.5 nm was studied. Photoluminescence spectra and its decay shown that for these systems the supplemental photosensitization of recombination luminescence of Ag₂S QDs (1200 nm) from the region of TH⁺ fluorescence (618 nm) is possible. It was found that the average lifetime of TH⁺ molecules luminescence is shortened during their association with Ag₂S QDs. Approximation of luminescence decay by stretched exponent with value of parameter β =?0.5 indicates on the inductive-resonance dipole-dipole (Förster) mechanism of nonradiative energy transfer (FRET). The efficiency of FRET was 0.29–0.41.     

Radiation hardness of CsBr:Eu

In this study,results on the radiation damage of the storage phosphor CsBr:Eu²⁺ are presented. It is shown that a high X-ray dose causes a significant deterioration of the photostimulated luminescence accompanied by a degradation of the UV-excited Eu²⁺ fluorescence. Since no related dose-dependent increase of Eu³⁺ luminescence is observed, the decrease of Eu²⁺ fluorescence is attributed to an agglomeration of Eu²⁺ leading to luminescence quenching. The correlated diffusivity of Eu²⁺ ions is ascribed to the presence of aggregated F-centres such as M_Eu-centres observed by means of absorption spectroscopy.     

The influence of low-temperature silver-ion exchange on the spectral-luminescent properties of fluorophosphate glasses doped with PbSe

Changes in the absorption and luminescence spectra of fluorophosphate glasses doped with PbSe caused by low-temperature Ag⁺–Na⁺ ion exchange are considered. It is found that the silver distribution gradient in a near-surface layer about 16 μm thick leads to two different processes of interaction between metal and semiconductor nanoparticles. PbSe molecular clusters and quantum dots more efficiently grow in deep layers with a low silver concentration. The near-surface glass layers with a high silver concentration exhibit formation of Ag metal nanoparticles, on the surface of which interaction with PbSe molecular clusters leads to the formation of Ag–Se–Pb bonds, which transform into Ag₂Se layers in the process of heat treatment. The appearance of the new phase is confirmed by X-ray diffraction.     

Luminescent Properties of Hybrid Nanostructures Based on Quantum Dots of CdS,Europium 1,3-Diketonate,and Methylene Blue Molecules

The luminescent properties of hybrid nanostructures constructed from colloidal quantum dots (QDs) of CdS passivated with thioglycolic acid, europium(III) tris(tenoyltrifluoroacetonate), and methylene blue dye molecules are studied. Spectral features typical for the formation of core/shell QDs of the CdS/CdS:Eu³⁺ type are found. It is noted that the adsorption of the europium complex at the QD interfaces and the formation of QDs of the CdS/TGA/Eu³⁺ are probable. Spectral patterns that reveal nonradiative energy transfer from the recombination luminescence centers of CdS QDs to the Eu³⁺ ions in the CdS/CdS:Eu³⁺ and CdS/TGA/Eu³⁺ structures are obtained. This is manifested in quenching the recombination luminescence of QDs and in the ignition of the intracentric luminescence of Eu³⁺, which enhance with an increase in the concentration of the europium complex. When such structures are combined with methylene blue molecules, the half-width of the absorption spectra is found to increase by 10–15% with an unchanged position of the absorption band maximum. With an increase in the concentration of methylene blue molecules, decreases in the intensity of the recombination luminescence band of CdS QDs at a wavelength of 530 nm and in the luminescence intensity of Eu³⁺ ions and simultaneously the rise up of the fluorescence of methylene blue at a wavelength of about 675 nm are observed. At the same time, a decrease in the luminescence lifetime of the bands of QDs and europium ions are observed. It is concluded that the nonradiative excitation energy transfer from both the recombination luminescence centers and Eu³⁺ ions to methylene blue molecules takes place.     

Fabrication of composite based on GeSi with Ag nanoparticles using ion implantation

Comparative analysis of the structural and optical properties of composite layers fabricated with the aid of implantation of single-crystalline silicon (c-Si) using Ge⁺ (40 keV/1 × 10¹⁷ ions/cm²) and Ag⁺ (30 keV/1.5 × 10¹⁷ ions/cm²) ions and sequential irradiation using Ge⁺ and Ag⁺ ions is presented. The implantation of the Ge⁺ ions leads to the formation of Ge: Si fine-grain amorphous surface layer with a thickness of 60 nm and a grain size of 20–40 nm. The implantation of c-Si using Ag⁺ ions results in the formation of submicron porous amorphous a-Si structure with a thickness of about 50 nm containing ion-synthesized Ag nanoparticles. The penetration of the Ag⁺ ions in the Ge: Si layer stimulates the formation of pores with Ag nanoparticles with more uniform size distribution. The reflection spectra of the implanted Ag: Si and Ag: GeSi layers exhibit a sharp decrease in the intensity in the UV (220–420 nm) spectral interval relative to the intensity of c-Si by more than 50% owing to the amorphization and structuring of surface. The formation of Ag nanoparticles in the implanted layers gives rise to a selective band of the plasmon resonance at a wavelength of about 820 nm in the optical spectra. Technological methods for fabrication of a composite based on GeSi with Ag nanoparticles are demonstrated in practice.     

ENHANCED PHOTOLUMINESCENCE OF Eu(III)-ANCHORED POROUS ANODIC ALUMINA FILM

We report here the enhanced luminescence of Eu(III)-anchored porous anodic alumina prepared by self-assembling Eu(III) acetylacetonate, and investigate the luminescence mechanisms. Porous anodic alumina can emit visible light due to a lot of oxygen vacancies formed in the anodic oxidation. The existence of oxygen vacancies resulted in e^?-h⁺ pairs when excited. Eu(II) exists stably by forming Eu²⁺-hole complexes. The enhanced luminescence of Eu(III)-anchored porous anodic alumina is attributed to the complex luminescence of e^?-h⁺ through luminescence center Eu²⁺.     

Fabrication of silver nanosheets on quartz glass substrates through electroless plating approach

Silver nanosheets (NSs) have been synthesized by an electroless plating approach using a complexation mechanism of triethanolamine (TEA) and Ag⁺ to reduce the oxidation–reduction potential difference and slow down the deposition speed of Ag on quartz glass substrates. The synthesized Ag NSs with 500 nm in edge length and 30 nm in thickness stand on the substrates and are dispersed uniformly. The formation mechanism of Ag NSs is proposed. The formation of Ag NSs is attributed to the molar ratio of AgNO₃ to TEA, the concentration of AgNO₃ and the influence of reaction temperature. This study is important in vertical immobilization Ag NSs on solid substrates, which could provide substrates for catalysis or surface-enhanced Raman scattering.     

Monitoring of the Proton Electrochemical Gradient in Reconstituted Vesicles: Quantitative Measurements of Both Transmembrane Potential and Intravesicular pH by Ratiometric Fluorescent Probes

Proteoliposomes carrying reconstituted yeast plasma membrane H⁺-ATPase in their lipid membrane or plasma membrane vesicles are model systems convenient for studying basic electrochemical processes involved in formation of the proton electrochemical gradient (Δμ_H ⁺) across the microbial or plant cell membrane. Δψ- and pH-sensitive fluorescent probes were used to monitor the gradients formed between inner and outer volume of the reconstituted vesicles. The Δψ-sensitive fluorescent ratiometric probe oxonol VI is suitable for quantitative measurements of inside-positive Δψ generated by the reconstituted H⁺-ATPase. Its Δψ response can be calibrated by the K⁺/valinomycin method and ratiometric mode of fluorescence measurements reduces undesirable artefacts. In situ pH-sensitive fluorescent probe pyranine was used for quantitative measurements of pH inside the proteoliposomes. Calibration of pH-sensitive fluorescence response of pyranine entrapped inside proteoliposomes was performed with several ionophores combined in order to deplete the gradients passively formed across the membrane. Presented model system offers a suitable tool for simultaneous monitoring of both components of the proton electrochemical gradient, Δψ and ΔpH. This approach should help in further understanding how their formation is interconnected on biomembranes and even how transport of other ions is combined to it.     

Influence of silver on the Sm<Superscript>3+</Superscript> luminescence in “Aerosil” silica glasses

The introduction of silver into the samarium-containing silica glasses prepared by the original solgel method leads to the formation of complex optical centers involving samarium ions and simple and/or complex silver ions. These centers are characterized by the effective sensitization of Sm³⁺ luminescence by Ag⁺, (Ag₂)⁺, and (Ag⁺)₂ ions according to the exchange mechanism for, at least, Sm³⁺-Ag⁺ centers. The formation of Sm-Ag centers is accompanied by an increase in the concentration of nonbridging oxygen ions, which prevent the reduction of silver ions by hydrogen. Silver nanoparticles formed in small amounts upon this reduction are effective quenchers of luminescence from the corresponding excited states of Sm³⁺ ions.     

Synthesis,Characterization and Applications of Schiff Base Chemosensor for Determination of Cr(III) Ions

The development of a highly sensitive, selective, and efficient sensor for the determination and detection of Cr(III) ions remains a great challenge. Recently, some fluorescent chemosensors have been developed for the recognition of Cr(III) ions. But, the main drawbacks of the reported fluorescent chemosensors are the lack of selectivity and interference of anions and other trivalent cations. Herein, we designed and synthesized a novel thiazole-based fluorescent and colorimetric Schiff base chemosensor SB2 for the detection of Cr(III) ion by chemodosimetric approach. Using different analytical techniques including UV–vis, ¹³C-NMR, ¹H-NMR, and FT-IR analysis the chemosensor SB2 was structurally characterized. The fully characterized chemosensor SB2 was used for the spectrofluorimetric and colorimetric detection of Cr(III) ions. Interestingly, chemosensor SB2 upon interaction with various metal cations including Ni²⁺, Na⁺, Cd²⁺, Ag⁺, Mn²⁺, K⁺, Zn²⁺, Cu²⁺, Hg²⁺, Co²⁺, Pb²⁺, Mg²⁺, Sn²⁺, Al³⁺ and Cr³⁺ displays highly selective and sensitive fluorescent (turn-on) and colorimetric (yellow to colorless) response toward Cr(III) ions. The fluorescence and UV–vis techniques confirmed the selective hydrolysis of azomethine group (-C?=?N-) of Schiff base chemosensor SB2 by Cr(III) ions. As a result, the fluorescence enhancement was observed that is corresponding to 2-hydroxy-1-nepthaldehyde (fluorophore). The chemosensor SB2 exhibits high interference performance towards Cr(III) ions over other metal cations in a wide pH range. Mover, the quite low detection limit was calculated to be 0.027 µg ml-1 (0.5 µM) (3σ/slop), lower than the maximum tolerable limits of Cr(III ions (10 µM) in drinking water permitted by the United States Environmental Protection Agency (EPA). These results show that chemosensor SB2 has great potential to detect selectively Cr(III) ions in the agricultural, environmental and biological analysis system.

Graphical Abstract