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Optical Properties of Red-Emitting Rb2Bi(PO4)(MoO4):Eu3+ Powders and Ceramics with High Quantum Efficiency for White LEDs
摘要： There are several key requirements that a very good LED phosphor should meet, i.e., strong absorption, high quantum e?ciency, high colour purity, and high luminescence quenching temperature. The reported Rb2Bi(PO4)(MoO4):Eu3+ phosphors have all these properties. The Rb2Bi(PO4)(MoO4):Eu3+ phosphors emit bright red light if excited with near-UV radiation. The calculated colour coordinates show good stability in the 77–500 K temperature range. Moreover, sample doped with 50% Eu3+ possesses quantum e?ciency close to unity. Besides the powder samples, ceramic disks of Rb2Eu(PO4)(MoO4) specimen were also prepared, and the red light sources from these disks in combination with near-UV emitting LED were fabricated. The obtained results indicated that ceramic disks e?ciently absorb the emission of 375 and 400 nm LED and could be applied as a red component in phosphor-converted white LEDs.
关键词： thermal quenching,luminescent ceramics,red phosphor,colour coordinates,quantum e?ciency,luminous e?cacy
更新于2025-09-16 10:30:52
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Quantum dots based “on-off” fluorescence probe for the selective detection of Cu2+ ion: Application to real samples analysis
摘要： Turn ‘On-Off’ quantum dot-based fluorescent probe has been developed for the selective detection of Cu2+. This strategy achieved by consecutively fluorescence enhancement and quenching of mercapto propionic acid (MPA) capped cadmium sulphide quantum dots (MPA-CdS QDs) by the addition of D-penicillamine (D-PA) and Cu2+ respectively. After successive addition of Cu2+ in CdS QDs- (D-PA) system, the fluorescence intensity of quantum dots decrease due to the removal of D-PA molecules from the surface of QDs as well as selective ion exchange process takes place between Cu2+ and Cd2+ at the surface of QDs. At optimal conditions, probe offers a good response in the linear range between 4 ng/mL and 40 ng/mL with LOD 2.71 ng/mL. This reported strategy is a very simple and selective towards Cu2+. Hence, a new method for the potential detection of Cu2+ in real pharmaceutical samples can be developed by using QDs-based fluorescence probe.
关键词： Fluorescence probe,quantum dots,pharmaceutical sample,quenching
更新于2025-09-12 10:27:22
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Carbon quantum dots (CQDs) modified ZnO/CdS nanoparticles based fluorescence sensor for highly selective and sensitive detection of Fe(III)
摘要： A simple and fast spectrofluorimetric method coupled with carbon quantum dots (CQDs) modified ZnO/CdS nanoparticles was developed for the detection of Ferric iron (Fe(III)). The fluorescence of CQDs/ZnO/CdS NPs was effectively quenched by Fe(III) due to the strong interaction between the CQDs/ZnO/CdS NPs and Fe(III). In addition, the detection limit of Fe(III) was about 1.72 × 10^-7 M. The effect of foreign ions on the fluorescence intensity of CQDs/ZnO/CdS NPs showed that the interference response in detecting of Fe(III) ions was low. Moreover, the quenching of Fe(III) and CQDs/ZnO/CdS NPs was discussed to be a static quenching procedure, which was proved by quenching constant KSV and fluorescence lifetime τ. The study of thermodynamics showed that the values of entropy change (?S) and enthalpy change (?H) were both positive, and the values of free energy (?G) was negative, which implied that the weak interaction of the molecular between CQDs/ZnO/CdS NPs and Fe(III) was hydrophobic force, and the quenching process was endothermic and spontaneous.
关键词： Static quenching,Ferric iron,CQDs/ZnO/CdS NPs,Fluorescence sensor
更新于2025-09-12 10:27:22
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Design of new Imidazole-derivative dye having donor-Π-acceptor moieties for highly efficient organic-dye-sensitized solar cells
摘要： In the present work, we have synthesised donors/acceptor substituted derivative of imidazole 4-(1-(3-chloro-4-nitrophenyl)-4,5-diphenyl-1H-imidazol-2-yl)benzoic acid (CNI) via one-pot synthetic method and has been characterized by spectroscopic methods such as IR, SEM and EDX. The photophysical properties like, solvatochromic shift and quantum yield of the CNI dye were found to be 1.85% and 0.57 respectively. The increase in absorbance and decrease in fluorescence spectra with different concentrations of TiO2 nanoparticles confirmed the possibility of interactions between dye and TiO2 nanoparticles. The Rehm-Weller relation suggests that, decrease in fluorescence of CNI dye was due to photo-induced electron transfer process and the Stern-Volmer studies suggest that, the fluorescence quenching mechanism was due to combined dynamic and static quenching process. The theoretical and experimental methods. Further, photosensitization of TiO2 nanoparticles from CNI dye has been investigated using absorption, steady state and time resolved fluorescence methods. Photovoltaic energy conversion efficiency and fill factor of fabricating CNI dye sensitized solar cell.
关键词： Dye sensitized solar cell (DSSC),TiO2 nanoparticles,Photo induced Electron transfer,Fluorescence quenching,Imidazoles derivatives
更新于2025-09-12 10:27:22
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Ultrafast hole extraction from photoexcited colloidal CdSe quantum dots coupled to nitroxide free radicals
摘要： Organic free radicals related to the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical are known as photoluminescence-quenchers when coupled to group II-chalcogenide colloidal quantum dots (QDs), but the mechanism responsible for this phenomenon has so far remained unresolved. Using a combination of time-resolved photoluminescence and transient absorption spectroscopies, we demonstrate that photoexcited colloidal CdSe QDs coupled to 4-amino-TEMPO undergo highly efficient reductive quenching, that is, hole transfer from the valence band of the quantum dot to the organic paramagnetic species. Interestingly, the process is shown to occur on a subpicosecond time scale for bound 4AT; such a large rate constant for the extraction of holes from photoexcited CdSe QD by a molecular species is rare and underlines the potential that TEMPO derivatives can play in mediating efficient redox processes involving colloidal CdSe QDs.
关键词： TEMPO,photoluminescence quenching,ultrafast spectroscopy,colloidal quantum dots,hole transfer
更新于2025-09-12 10:27:22
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Defect characterization of slow-cooled and quenched samples of calcium-copper-titanate through positron annihilation spectroscopy
摘要： Positron annihilation lifetime and Doppler-broadened gamma-ray spectra have been analyzed for slow-cooled and thermally quenched polycrystalline samples of calcium-copper-titanate. Two positron lifetimes revealing the characteristic defects in the respective samples were carefully analyzed to compare and contrast the significance of their origin and implication. A third component arising from positronium formation at the powdered particle surfaces has been considered in the analysis although its significance is lost in its very small intensity ((cid:1) 1.1–1.2%). In the quenched sample, the defect-specific long positron lifetime (s2) is found to larger and the mean lifetime smaller while its intensity I2 is found drastically smaller and the concentration of defects less by an order of magnitude as compared to the slow-cooled sample. The observed changes in electrical parameters of slow-cooled and quenched samples were found to have correlations with the positron annihilation lifetime and Doppler-broadened lineshape parameters.
关键词： defects,vacancies,positron annihilation,Calcium-copper-titanate,quenching
更新于2025-09-12 10:27:22
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Phototransferred thermoluminescence of annealed synthetic quartz: Analysis of illumination-time profiles, kinetics and competition effects
摘要： Phototransferred thermoluminescence (PTTL) induced from annealed synthetic quartz using 470 nm blue light is reported. The quartz was annealed at 900oC for 10, 30 and 60 minutes prior to use. A glow curve of conventional TL measured at 1oC s-1 following irradiation to 200 Gy for the sample annealed for 10 minutes shows six peaks at 90, 122, 176, 210, 240 and 340oC. The sample annealed for 30 minutes has peaks at 80, 110, 136, 196, 240 and 330oC. Similarly, the sample annealed for 60 minutes also has six peaks at 80, 120, 134, 188, 235 and 340oC. For ease of reference, these are labelled I-VI respectively. Peaks observed under PTTL are referred to as A1 onwards. Of the six peaks, only the first three are reproduced under phototransfer for the sample annealed for 60 minutes. When the duration of annealing was reduced to 10 minutes, PTTL is induced only at peaks A1 and A3. Interestingly, for the intermediate duration of annealing of 30 minutes, the only peak that appears under phototransfer is the first one, A1. For quartz annealed for 10 minutes, the PTTL appears as long as the preheating temperature does not exceed 560oC. On the other hand, in the quartz annealed for 30 and 60 minutes, PTTL only appears for preheating to and below 450oC. This shows that the occupancy of deep electron traps at temperatures beyond 450 or 560oC is low in the said samples. The activation energy for peaks A1 and A3 was found to be about 0.68 eV. The PTTL peaks were studied for thermal quenching and peaks A1 and A3 were determined to be subject to this effect. The activation energy for thermal quenching was determined as 0.62 ± 0.04 eV in analysis using peak A1. In all cases, the PTTL intensity goes through a peak as a function of illumination time. The experimental dependence of PTTL intensity on illumination time is modelled using sets of coupled linear differential equations based on systems of donors and acceptors whose number is determined by preheating temperature. Competition effects involved in the PTTL have been discussed.
关键词： competition effects,phototransferred thermoluminescence,synthetic quartz,Annealing,thermal quenching
更新于2025-09-12 10:27:22
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Study on the preparation of water-soluble AgInS2 quantum dots and their application in the detection of ciprofloxacin
摘要： Water-soluble AgInS2 quantum dots (AIS QDs) were prepared by hot-injection method with thioglycolic acid (TGA) as the stabilizer. The fluorescence of as-prepared AIS QDs could be quenched effectively by ciprofloxacin. Herein, a method for the content determination of ciprofloxacin based on the fluorescence quenching effect was explored. The experimental results showed that the particle size of AIS QDs prepared at pH = 4 was about 3–8 nm, and the maximum fluorescence emission wavelength was centered at 626 nm at λex = 500 nm. The measured concentration range of ciprofloxacin could be adjusted by varying the amount of AIS QDs solution. When 0.40 mL AIS QDs solution was used for the content determination of ciprofloxacin, a good linearity relationship was achieved between the quenched efficiency of AIS QDs fluorescence and the concentration of ciprofloxacin in the range of 1.0–19.5 μg/mL, the correlation coefficient was 0.996, the detection limit of ciprofloxacin was 0.12 μg/mL, and the blank spike recoveries were in the range of 96.7–103.3%. The method is of wide detection range, excellent selectivity, high sensitivity and easy operability, could be applied for the content determination of ciprofloxacin in drugs.
关键词： AgInS2 quantum dots,Ciprofloxacin,Fluorescence quenching,Content determination
更新于2025-09-12 10:27:22
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CdTe Quantum Dots Modified with Cysteamine: A New Efficient Nanosensor for the Determination of Folic Acid
摘要： In this paper, we report the synthesis, characterization, and application of a new fluorescent nanosensor based on water-soluble CdTe quantum dots (QDs) coated with cysteamine (CA) for the determination of folic acid (FA). CdTe/CA QDs were characterized by high-resolution transmission electron microscopy, the zeta potential, and Fourier-transform infrared (FT-IR), UV-visible, and fluorescence spectroscopy. CdTe QDs coated with mercaptopropionic acid (MPA) and glutathione (GSH) were prepared for comparison purposes. The effect of FA on the photoluminescence intensity of the three thiol-capped QDs at pH 8 was studied. Only CdTe/CA QDs showed a notable fluorescence quenching in the presence of FA. Then, a nanosensor based on the fluorescence quenching of the CdTe QDs at pH 8 was explored. Under optimum conditions, the calibration curve showed a linear fluorescence quenching response in a concentration range of FA from 0.16 to 16.4 μM (R2 = 0.9944), with a detection limit of 0.048 μM. A probable mechanism of fluorescence quenching was proposed. The nanosensor showed good selectivity over other possible interferences. This method has been applied for FA quantification in orange beverage samples with excellent results (recoveries from 98.3 to 103.9%). The good selectivity, sensitivity, low cost, and rapidity make CdTe /CA QDs a suitable nanosensor for FA determination.
关键词： electron transfer,folic acid nanosensor,positive quantum dots,fluorescence quenching
更新于2025-09-12 10:27:22
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Development of all-fiber Fabry-Perot pulse laser with a fiber type saturable absorber and improvement of the oscillation characteristics
摘要： The authors developed high-concentration erbium doped fiber as a saturable absorber, making use of its concentration quenching. Then, they developed an all-fiber Fabry-Perot pulse laser with high-concentration erbium doped fiber and demonstrated that it enables stable and passive pulse oscillation regardless of disturbance. Furthermore, they successfully improve power efficiency and shortening pulse width to 1.8 μs by optimizing the structure of the fiber laser.
关键词： Er doped fiber,fiber laser,concentration quenching,all-fiber passive Q-switching,fiber-type saturable absorber
更新于2025-09-12 10:27:22