Radiation chemistry of tris(acetylacetonato) cobalt(iii) in aqueous solutions

Abstract

On radiolysis tris(acetylacetonato) cobalt(III) in aqueous solutions is found to get reduced by reaction with (1) hydrated electrons, (2) H atoms, (3) OH radicals and (4) C₂H₂OH radicals. The bimolecular rate constants for the first three reactions, determined by competition kinetics are: 4 × 10¹⁰, 2.3 × 10⁹ and 4.7 × 10⁹ M^?1sec^?1 respectively. Absorption spectra of the irradiated solutions indicate the formation of bis(acetylacetonato) cobalt(II) from reaction (1), but not from (3). The total cobaltous yield in air-free solutions is given byG(Co⁺⁺) = 5.6 and 6.5 at pH 6.5 and 1 respectively. It appears that G_eaq- ∽ _H ⁺ G_oH ∽ 2.8 in neutral solutions. Considerations of material balance for the primary yields of radiolysis of water suggest the possibility that the so-called independent H-atoms in neutral solutions are probably excited water molecules or ion-pairs.     

Polymer microenvironmental effects on the photophysics of cinchonine dication

Photophysical properties of cinchonine dication (C⁺⁺) have been studied in protic and aprotic polymers by monitoring steady state and time resolved measurements. It is found to be sensitive towards the microenvironment of polymers. Edge excitation red shifted emission (EERS) is observed in all polymeric matrices. However, the magnitude of EERS is relatively high in protic as compared to aprotic polymer. Isobestic point in excitation spectra and three decay components in time resolved measurements indicate more than two trapped chemical species in the heterogeneous environment of the polymer. Solute-polymer interactions are found to produce the third decay channel, unlike in solution phase and may be useful to understand the polymer microenvironment.     

Spectrophotometric Study of Zinc,Cadmium and Lead Complexes with Murexide in Binary Ethanol-Water Mixtures

The complexation reactions between murexide and Zn²⁺, Cd²⁺ and Pb²⁺ ions in C₂H₅OH-H₂ mixtures have been investigated spectrophotometrically. Formation constants of the resulting 1:1 complexes were determined and found to vary in the order Pb²⁺ > Cd²⁺ > Zn²⁺, in all binary ethanol-water mixtures used. There is an inverse relationship between the complex formation constants and amount of water in the mixed solvent. A linear relationship was observed between log K_f for complexes and the mole fraction of ethanol.     

Novel room temperature ionic liquid for fluorescence enhancement of Eu and Tb

The newly prepared ionic liquid, 1-butyl-3-methylimidazolium benzoate, ([bmim][BA]), was found to enhance the fluorescence of Eu³⁺ and Tb³⁺. The fluorescence enhancement resulted from a sensitization of the lanthanide fluorescence by the benzoate anion of the ionic liquid, [bmim][BA], and a reduction in the non-radiative channels in the non-aqueous environment provided by the ionic liquid. However, the fluorescence enhancement of the lanthanides in the ionic liquid was limited due to the operation of the inner filter effect, which resulted from the strong absorption of the benzoate. The inner filter effect was minimized by observing the Eu³⁺ fluorescence using a front face geometry and also by diluting the lanthanide-[bmim][BA] system, using another ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]), as a solvent. In the case of Tb³⁺, the emission from the lanthanide was masked by the strong emission from the ionic liquid in the region 450-580 nm. The long lived Tb³⁺ emission was therefore observed using delayed gated detection, where an appropriate delay was used to discriminate against the short lived emission from the ionic liquid. The large fluorescence enhancement due to ligand sensitized fluorescence observed with [bmim][BA] diluted in [bmim][Tf₂N], leads to nanomolar detection of the lanthanides. This is, to the best of our knowledge, the first report of an ionic liquid being employed for ligand sensitized fluorescence enhancement of lanthanides.     

NIR to visible upconversion in Er/Yb co-doped CaYAl3O7 phosphor obtained by solution combustion process

Using the combustion synthesis, CaYAl₃O₇:Er³⁺ phosphor powders co-doped with Yb³⁺ have been prepared at low temperatures (550 °C) in a few minutes. Formation of the compound was confirmed by X-ray powder diffraction. Near-infrared to visible upconversion fluorescence emission in the Er³⁺ doped CaYAl₃O₇ phosphor powder has been observed. The effect of co-doping with triply ionized ytterbium in the CaYAl₃O₇:Er³⁺ phosphor has been studied and the process involved is discussed.     

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.     

Effect of cation mixing on luminescence of Eu in SrCl2

SrCl₂ forms solid solutions of various compositions with BaCl₂ and CaCl₂. Orthorhombic and tetragonal phases are also known to occur in the SrCl₂-CaCl₂ system. Though efficient emission of Eu²⁺ in SrCl₂ and CaCl₂ is known, there are no reports available on Eu²⁺ luminescence in the solid solutions and other phases. Investigations on these lines were carried out and the results are presented in this paper. Very intense emission comparable to that of the commercial lamp phosphors was observed for the solid solutions while the intensities for the orthorhombic and tetragonal phases are an order of magnitude smaller. Emission wavelengths do not vary much while excitation spectra for the solid solutions are much enhanced in the near UV region (350-400 nm). It is suggested that these results will be significant for developing phosphors with near UV excitations needed in applications such as solid state lighting.     

Studies of the electrochemical reduction processes of Bi, HTeO2 and their mixtures

The reduction process of Bi³⁺, HTeO₂⁺ and their mixtures on Au electrode surface was studied by cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. XRD and EDS methods were also used to measure the reductive products prepared under different potentials and provide the evidences of the reactions. The results indicate that the reduction of HTeO₂⁺ occurs at more positive potential than that of Bi³⁺, but its reduction rate is slower and adsorption phenomenon exists during its reduction process. Bi₂Te₃ compound can be obtained potentiostatically at a proper potential in all the mixed solutions with concentration ratio CHTe+O₂/CBi3+ in our research range (0.1-10). But pure Bi₂Te₃ compound can only be obtained at 42 mV in the solution with concentration ratio CHTe+O₂/CBi3+ equaling to 1. And the formation of Bi₂Te₃ compound is an inductive co-depositing process: (1) HTeO₂⁺ + 4e⁻ + 3H⁺ → Te⁰ + 2H₂O, (2) 3Te⁰ + 2Bi³⁺ + 6e⁻ → Bi₂Te₃.     

Luminescent properties of (Y,Gd)BO3:Bi,RE (RE=Eu, Tb) phosphor under VUV/UV excitation

Bi³⁺- and RE³⁺-co-doped (Y,Gd)BO₃ phosphors were prepared and their luminescent properties under vacuum ultraviolet (VUV)/UV excitation were investigated. Strong red emission for (Y,Gd)BO₃:Bi³⁺,Eu³⁺ and strong green emission for (Y,Gd)BO₃:Bi³⁺,Tb³⁺ are observed under VUV excitation from 147 to 200 nm with a much broader excitation region than that of single Eu³⁺-doped or Tb³⁺-doped (Y,Gd)BO₃ phosphor. Strong emissions are also observed under UV excitation around 265 nm where as nearly no luminescence is observed for single Eu³⁺-doped or Tb³⁺-doped (Y,Gd)BO₃. The luminescence enhancement of Bi³⁺- and RE³⁺-co-doped (Y,Gd)BO₃ phosphors is due to energy transfer from Bi³⁺ ion to Eu³⁺ or Tb³⁺ ion not only in the VUV region but also in the UV region. Besides, host sensitization competition between Bi³⁺ and Eu³⁺ or Tb³⁺ is also observed. The investigated phosphors may be preferable for devices with a VUV light 147-200 nm as an excitation source such as PDP or mercury-free fluorescent lamp.     

Intense ultraviolet upconversion luminescence of Yb and Tb co-doped glass ceramics containing SrF2 nanocrystals

The preparation and upconversion luminescence properties of the Yb³⁺ and Tb³⁺ co-doped glass ceramics containing SrF₂ nanocrystals were investigated. The formation of SrF₂ nanocrystals was confirmed by X-ray diffraction and transmission electron microscopy. Both microstructural and spectral analysis indicated that the Yb³⁺ and Tb³⁺ ions were enriched in the precipitated SrF₂ nanocrystals, which provide much lower phonon vibration energy than the glass matrix. Due to the efficient cooperative sensitization from Yb³⁺ to Tb³⁺ and the relatively low maximum phonon energy of SrF₂ nanocrystals, the Yb³⁺ and Tb³⁺ co-doped glass ceramics exhibited intense upconversion luminescence, including ultraviolet emission at 382 nm.     

Spectroscopic analysis of the interaction between chromium (III) and apoovotransferrin

Ovotransferrin (OTf) is a main member of the transferrin family that functions both as an iron transporter and an antibacterial agent. In this study, the thermodynamic property of the interaction between chromium (III) and ovotransferrin was investigated. The conditional binding constants for Cr³⁺ binding to the protein were determined by difference UV spectroscopy and were found to be log K_C=13.08±0.24 and log K_N=5.65±0.12. It was found that Cr³⁺ preferentially binds to the C-terminal site over the N-terminal site under these experimental conditions. The conformational changes in apoovotransferrin (apoOTf) during Cr³⁺ binding were studied by fluorescence spectroscopy using 2-p-toluidinylnaphthalene-6-sulfonate (TNS) as the fluorescence probe and by circular dichroism (CD) spectroscopy. The results show that a large conformational change in apoOTf can be attributed to binding of Cr³⁺ to the N-terminal site, instead of the C-terminal site. In addition, the binding of Cr³⁺ to apoOTf stabilizes the structure of OTf as determined by guanidine hydrochloride denaturation studies. These findings help advance our understanding of the biological effects of Cr³⁺.     

Tm3+/Yb3+ ∶LaF3纳米体系中掺杂Yb3+ 离子对Tm3+ 离子荧光发射的影响

为研究Yb³⁺离子浓度变化对Tm³⁺离子在蓝色波段荧光强度的影响,以NaF和La(NO₃)₃为原料,采用水热法制备了Tm³⁺和Yb³⁺共掺的Tm³⁺/ Yb³⁺∶LaF₃纳米颗粒.用X射线衍射对LaF₃纳米颗粒进行表征的结果显示,纳米晶体结构呈六方相.透射电镜的观测结果显示,纳米颗粒样品大小均匀、分散性良好.在波长为800 nm的激光激发下,观测到了上转换蓝光发射,其中包括波长为474 nm和479 nm的较强的荧光辐射(相应的跃迁为1G4→3H6)和波长位于450 nm的强度较弱的荧光发射(相应的跃迁为1D2→3F4).通过观测不同Yb³⁺离子浓度条件下共掺Tm³⁺/Yb³⁺∶LaF₃样品的荧光光谱,研究了Yb³⁺离子掺杂浓度对于Tm³⁺离子的荧光发射的影响,并探讨了产生这种现象的原因.研究结果显示,对于1G4→3H6跃迁产生的荧光发射(474 nm),当Yb³⁺离子浓度增大时,反向能量传递速率的增加导致了荧光强度的增大.然而,当Yb³⁺离子浓度增大到一定程度时,Yb³⁺离子激发态能级寿命的减少将引发荧光强度的下降.相比较而言,Yb³⁺离子的浓度的变化对于1D2→3F4跃迁产生的位于450 nm处荧光强度的影响较弱.     

Fluorescence and persistent spectral hole burning of Eu in Ge-Ga-S-KBr glasses

Fluorescence and efficient persistent spectral hole burning of Eu³⁺ at 77 K were observed in chalcohalide glasses. The depth of the hole was approximately 30% after a burning process of 1 min with 50 mW power, and it was completely erased with Ar⁺ laser irradiation. The hole survived room temperature heat treatment and showed good thermal stability. The hole-burning mechanism was most probably the photo-reduction of Eu³⁺→Eu²⁺. Fluorescence from Eu³⁺ decreased with increasing temperature and disappeared at the temperature above ∼130 K.     

Fluorescence enhancement of oxide fluoride glass co-doped with TbF3 and SmF3

The fluorescence property of xTbF₃-BaF₂-AlF₃-GeO₂+ySmF₃ (x=0.01-40 mol%, y=0-5 wt%) glasses were investigated. The enhancement of Sm³⁺ fluorescence was recognized in the presence of Tb³⁺. Increasing Tb³⁺ content, the emission color changed from green to orange. When the intensity of fluorescence at 540 nm originated from Tb³⁺ is compared with that at 600 nm originated from Sm³⁺, the information about the concentration quenching of Tb³⁺ and Sm³⁺ was obtained. From these results, rare earth ions were dispersed identically in the glasses. After heating to 673 K or cooling to 77 K, the emission color of 20TbF₃-20BaF₂-10AlF₃-50GeO₂/mol%+0.05 wt% SmF₃ glass was reversibly changed from orange to green. In addition, while the emission from 10TbF₃-20BaF₂-10AlF₃-60GeO₂+0.01 wt% SmF₃ glass was green, its crystallized sample, prepared by annealing at 1073 K, exhibited an orange emission due to Sm³⁺ at room temperature.     

Polyethylene terephthalate (PET) bulk film analysis using C60, Au3, and Au primary ion beams

The damage characteristics of polyethylene terephthalate (PET) have been studied under bombardment by C₆₀⁺, Au₃⁺ and Au⁺ primary ions. The observed damage cross-sections for the three ion beams are not dramatically different. The secondary ion yields however were significantly enhanced by the polyatomic primary ions where the secondary ion yield of the [M + H]⁺ is on average 5× higher for C₆₀⁺ than Au₃⁺ and 8× higher for Au₃⁺ than Au⁺. Damage accumulates under Au⁺ and Au₃⁺ bombardment while C₆₀⁺ bombardment shows a lack of damage accumulation throughout the depth profile of the PET thick film up to an ion dose of ∼1 × 10¹⁵ ions cm⁻². These properties of C₆₀⁺ bombardment suggest that the primary ion will be a useful molecular depth profiling tool.     

STUDIES ON COPPER-CONTAINING NAD GLYCOHYDROLASE FROM AGKISTRODON ACUTUS VENOM BY FLUORESCENCE AND CD SPECTROSCOPY

ABSTRACT

The properties of NAD Glycohydrolase (NADase), purified from Agkistrodon acutus venom, have been studied by fluorescence and CD spectroscopy. The fluorescence intensities of NADase decrease by about 1% or 3% when the concentrations of I^? ion are 0.1 mol/L or 0.2 mol/L in the NADase solutions, respectively. However, the fluorescence intensities of the NADase are quenched by about 25% and 48%, respectively, with further addition of 1 mmol/L EDTA into solutions. CD spectra also suggested that EDTA could remove Cu²⁺ ion from NADase molecule and the conformation of NADase changed much. So Cu²⁺ ion is very important to maintain the geometrical structure of NADase.     

Ultraviolet excitation of rare-earth-doped YSZ crystals

Abstract

The optical properties of nominally pure and Er³⁺- or Pr³⁺ -doped yttria-stabilized zirconia single crystals were investigated under UV light excitation. In the excitation spectra of both types of doped crystals, a broad UV band is observed. Under excitation with light of different wavelengths inside this band, the luminescence features of the doped crystals are different. YSZ: Pr³⁺ samples exhibit the characteristic 4f → 4f emission of the Pr³⁺ ions. In YSZ: Er³⁺ crystals, both the Er³⁺ ion and the intrinsic luminescence are observed. Host to Er³⁺ ion radiative energy-transfer is also demonstrated. No dependence of the transfer process with the excitation wavelength was found. These results suggest that the UV band in Er³⁺ -doped crystals is associated with the lattice-dopant ion interaction rather than with the 4f5d interconfigurational band of the Er^3? ions.     

On the fluorescence enhancement mechanism of Er3+ in germanate glass containing silver particles

The spectral properties of trivalent erbium ions(Er3+) are systematically studied in a melt-quenched germanate glass(60 GeO2-20PbO-10BaO-10K2O-0.1Ag2O) containing silver(Ag) particles.Thermal treatment of the material leads to the precipitation of Ag particles as observed by transmission electron microscopy and confirmed by absorption spectrum for the obvious surface plasmon resonance peak of Ag particles.The fluorescence from Er3+ in the 10-min-annealed sample with Ag particles is found to be 4.2 times enhanced compared with the unannealed sample excited by 488-nm Ar+ laser.A comparison is made between a spectral study performed on the unannealed Er3+-doped sample and the one annealed for 20 min.The data of absorption cross section and Judd-Ofelt intensity parameters show the agreement between the two samples no matter whether there are Ag particles,indicating that the introduction of Ag particles by post-heat treatment has no effect on the crystal field environment of Er3+ ions.The fluorescence enhancement is attributed to the surface plasmon oscillations of Ag particles in germanate glass.     

Fluorescence enhancement effect for the determination of curcumin with yttrium(III)—curcumin—sodium dodecyl benzene sulfonate system

It is found that the fluorescence of curcumin is greatly enhanced by yttrium(III) (Y³⁺) in the presence of sodium dodecyl benzene sulfonate. Based on this, a sensitive fluorimetric method for the determination of curcumin in aqueous solution is proposed. In the potassium hydrogen phthalate (KHP) buffer, the fluorescence intensity of curcumin is proportional to the concentration of curcumin in the range of 7.37×10⁻⁴-0.18, 0.18-2.95 μg mL⁻¹ and the detection limit is 0.1583 ng mL⁻¹. The actual samples are satisfactorily determined. In addition, the interaction mechanism is also studied.     

Pr3+/Ho3+共掺Ge-Ga-Se玻璃的2.9 μm荧光特性的研究

采用熔融冷却法制备了系列Ho³⁺/Pr³⁺共掺的Ge₂₅Ga₁₀Se₆₅玻璃样品,测试了样品的吸收光谱以及908 nm激光抽运下的中红外荧光光谱和Ho³⁺离子⁵I₇能级寿命.计算了Ho³⁺:⁵I₇→⁵I₈发射截面和Pr³⁺:³H₄→³F₂吸收截面,讨论了Ho³⁺,Pr³⁺离子之间的能量转移效率及Pr³⁺离子浓度的影响.通过拟合Ho³⁺离子2.0 μm荧光衰减曲线判断能量转移机理.结果表明,Ho³⁺掺杂Ge₂₅Ga₁₀Se₆₅玻璃中引入Pr³⁺离子可以有效提高Ho³⁺离子的2.9 μm荧光强度. 关键词： 中红外发光 硫系玻璃 3+/Pr³⁺共掺')" href="#">Ho³⁺/Pr³⁺共掺