Quantum Yield Measurements Research Articles

Ag nanowire-assisted low threshold WGM lasing from polymer optical fiber.

Whispering Gallery Mode (WGM) emission has been observed from Ag nanowire doped polymer optical fiber laser. Low threshold lasing and high photostability of the active medium has been noticed with a given concentration of Ag nanowires in the microcavity of the fiber. Quantum yield and lifetime measurements of the dye (active medium) with and without nanowires confirm that presence of nanowires enhance the rate of radiative decay of the fluorophore, thereby providing low pump pulse energy for the excitation of lasing modes in the cavity, as compared with a bare dye-doped polymer fiber laser.

Fluorescence Enhancement Through Incorporation of Chromophores in Polymeric Nanoparticles

Incorporation of a pyrene chromophore on the surface of polymeric nanoparticles results in its fluorescence enhancement. Quantum yield and lifetime measurements suggest that the enrichment in fluorescent signal is due to the increase in the rigidity of the environment surrounding the fluorophores and that it is dependent on the particle size.

Controlled Isotropic and Anisotropic Shell Growth in β-NaLnF4 Nanocrystals Induced by Precursor Injection Rate

Precise morphology and composition control is vital for designing multifunctional lanthanide-doped core/shell nanocrystals. Herein, we report controlled isotropic and anisotropic shell growth techniques in hexagonal sodium rare-earth tetrafluoride (β-NaLnF4) nanocrystals by exploiting the kinetics of the shell growth. A drastic change of the shell morphology was observed by changing the injection rate of the shell precursors while keeping all other reaction conditions constant. We obtained isotropic shell growth for fast sequential injection and a preferred growth of the shell layers along the crystal's c-axis [001] for slow dropwise injection. Using this slow shell growth technique, we have grown rod-like shells around different almost spherical core nanocrystals. Bright and efficient upconversion was measured for both isotropic and rod-like shells around β-NaYF4 nanocrystals doped with Yb3+/Er3+ and Yb3+/Tm3+. Photoluminescence upconversion quantum yield and lifetime measurements reveal the high quality of the core/shell nanocrystal. Furthermore, multishell rod-like nanostructures have been prepared with optically active cores and tips separated by an inert intermediate shell layer. The controlled anisotropic shell growth allows the design of new core/multishell nanostructures and enables independent investigations of the chemistry and physics of different nanocrystal facets.

Temperature dependent photoluminescence of Dy3+ doped LiCaBO3 phosphor

A single phase white light emitting Dy3+ doped LiCaBO3 phosphors were prepared by solid-state reaction method at 700 °C. The crystal structure properties were analyzed by utilizing powder X-ray Diffraction and followed by the profile fitting to calculate the lattice parameters. The FESEM, UV–Vis, photoluminescence excitation and emission spectra, decay time and quantum yield measurement were utilized to characterize the samples. The temperature dependent photoluminescence emission and decay times were recorded in the temperature range 100–480 K. The phosphor exhibits two emission bands at 485 nm (blue) and 578 nm (yellow) originating from the f–f transition of Dy3+. The optimized doping concentration for maximum emission intensity was 2 mol%. A near white emission was achieved with color co-ordinate (0.35, 0.39) and CCT value 4955 K. The material had excellent thermal and color stability. The absolute quantum yield is 0.25. So the near white emission, excellent thermal stability and suitable quantum yield of LiCaBO3: Dy3+ can be a promising candidate for near UV–LED pumped white light emitting diode.

Temperature-Dependent Hole Transfer from Photoexcited Quantum Dots to Molecular Species: Evidence for Trap-Mediated Transfer.

The effect of temperature on the rate of hole transfer from photoexcited quantum dots (QDs) is investigated by measuring the driving force dependence of the charge transfer rate for different sized QDs across a range of temperatures from 78 to 300 K. Spherical CdSe/CdS core/shell QDs were used with a series of ferrocene-derived molecular hole acceptors with an 800 meV range in electrochemical potential. Time-resolved photoluminescence measurements and photoluminescence quantum yield measurements in an integrating sphere were both performed from 78 to 300 K to obtain temperature-dependent rates for a series of driving forces as dictated by the nature of the molecular acceptor. For both QD sizes studied and all ligands, the Arrhenius plot of hole transfer exhibited an activated (linear) regime at higher temperatures and a temperature-independent regime at low temperatures. The extracted activation energies in the high-temperature regime were consistent across all ligands for a given QD size. This observation is not consistent with direct charge transfer from the QD valence band to the ferrocene acceptor. Instead, a model in which charge transfer is mediated by a shallow and reversible trap more accurately fits the experimental results. Implications for this observed trap-mediated transfer are discussed including as a strategy to more efficiently extract charge from QDs.

Bright luminescence of diamonds with Ge-V centers

We report on the quantum yield (η) and decay time (τ) measurements at room temperature for the bright red-orange (602nm) luminescence from new germanium-vacancy (Ge-V) centers in nano- and microcrystalline diamonds synthesized at high pressure and high temperature. The values η = 3 ± 1% and τ = 6.2±0.2ns were found. The Stokes shift measured as the energy difference between the maxima of the luminescence and luminescence excitation spectra is negligible. The relative intensity of the zero-phonon line constitutes up to 70% of the total intensity of the luminescence. Results of our ab initio DFT calculations for the ground-state electronic and vibrational structure of (Ge-V)- in diamond are presented and discussed.

Atmospheric Constraints on the Surface UV Environment of Mars at 3.9 Ga Relevant to Prebiotic Chemistry.

Recent findings suggest that Mars may have been a clement environment for the emergence of life and may even have compared favorably to Earth in this regard. These findings have revived interest in the hypothesis that prebiotically important molecules or even nascent life may have formed on Mars and been transferred to Earth. UV light plays a key role in prebiotic chemistry. Characterizing the early martian surface UV environment is key to understanding how Mars compares to Earth as a venue for prebiotic chemistry. Here, we present two-stream, multilayer calculations of the UV surface radiance on Mars at 3.9 Ga to constrain the surface UV environment as a function of atmospheric state. We explore a wide range of atmospheric pressures, temperatures, and compositions that correspond to the diversity of martian atmospheric states consistent with available constraints. We include the effects of clouds and dust. We calculate dose rates to quantify the effect of different atmospheric states on UV-sensitive prebiotic chemistry. We find that, for normative clear-sky CO2-H2O atmospheres, the UV environment on young Mars is comparable to young Earth. This similarity is robust to moderate cloud cover; thick clouds (τcloud ≥ 100) are required to significantly affect the martian UV environment, because cloud absorption is degenerate with atmospheric CO2. On the other hand, absorption from SO2, H2S, and dust is nondegenerate with CO2, meaning that, if these constituents build up to significant levels, surface UV fluence can be suppressed. These absorbers have spectrally variable absorption, meaning that their presence affects prebiotic pathways in different ways. In particular, high SO2 environments may admit UV fluence that favors pathways conducive to abiogenesis over pathways unfavorable to it. However, better measurements of the spectral quantum yields of these pathways are required to evaluate this hypothesis definitively. Key Words: Radiative transfer-Origin of life-Mars-UV radiation-Prebiotic chemistry. Astrobiology 17, 687-708.

Interaction between triethanolamine and singlet or triplet excited state of xanthene dyes in aqueous solution

Triethanolamine (TEOA) has been often used as a hole-scavenger in dye-sensitized semiconductor photocatalytic systems. However, the femtosecond time-resolved kinetics of the interaction between a sensitized dye and TEOA has not been reported in literatures. Herein, we selected four commonly used xanthene dyes, such as fluorescein, dibromofluorescein, eosin Y, and erythrosine B, and studied their ultrafast fluorescence quenching dynamics in the presence of TEOA in aqueous solution, respectively, by using both femtosecond transient absorption and time-resolved fluorescence measurements. We obtained the electron transfer rate from TEOA to each photoexcited xanthene dye in 2.0 M TEOA solution. We also obtained the intersystem crossing rate of each xanthene dye in aqueous solution with fluorescence quantum yield and lifetime measurements. Finally we found that TEOA mainly interacts with the singlet excited-state of fluorescein, dibromofluorescein, and eosin Y, and that TEOA can interact with both the singlet and triplet excited-states of erythrosine B in high concentration of TEOA aqueous solution.

Ultraviolet to near-infrared down-conversion in Bi3+–Yb3+ co-doped YAM phosphor

Abstract Direct measurements of external quantum yield (QY) were applied to down-converting phosphors of Y 4 Al 2 O 9 (YAM) co-doped with Bi 3+ and Yb 3+ . The QY measurements were combined with studies of photoluminescence (PL), photoluminescence excitation (PLE) and photoluminescence decay kinetics. It was found that the energy transfer occurs mainly from one of the four possible types of Bi 3+ centers in YAM, namely Bi 3+ (I), with excitation and emission maxima at 278 nm and 360 nm, respectively. The absolute QY measurements show large discrepancy between the measured quantum efficiencies of the UV to near-IR down-conversion process and the efficiencies estimated from the shortening of the Bi 3+ luminescence decay time. Results presented in the paper testify the conversion ratio (which should be 2.0 for an ideal quantum cutting mechanism) to be no more than 1.0 in the studied material.

Luminescence of ferrocene-modified pyrene derivatives for turn-on sensing of Cu2 + and anions

Detection and identification of metal ions by fluorescent turn-on sensors are challenging due to the quenching effect of most of the tested metal ions. In the present work, three ferrocene-modified pyrene-based probes 2–4 were synthesized to act as turn-on fluorescent sensors for Cu2+. The measurements of fluorescence quantum yield and fluorescence lifetime reveal that ferrocenyl unit can efficiently reduce the fluorescence emission of pyrene moiety. Steady-state fluorescence measurements find that the three ferrocene-modified fluorophores exhibit selective turn-on responses to Cu2+. Moreover, this turn-on effect to Cu2+ is highly influenced by the type of the counter ion. It is found that the presence of Cl− or NO3− could realize the turn-on response to Cu2+, whereas, the presence of SO42− or Ac− could not induce any fluorescence enhancement to Cu2+. Control experiments with ferrocene-free pyrene-based probe 1 reveal that the ferrocenyl unit plays the key role in the turn-on response to Cu2+. The possible mechanism for the turn-on responses is attributed to the oxidation behavior of Cu2+ to the ferrocene unit, which is confirmed by the control experiments with sodium ascorbate. Cyclic voltammetry measurements show that Cu2+ can influence the redox behaviors of ferrocenyl derivatives, which is also highly dependent on the anion of the copper salts. The influence of anion on the turn-on responses to Cu2+ was further used for anion detection and fluorescent logic gate.

Photocatalytic hydrogen production using mesoporous TiO2 doped with Pt

A series of mesoporous TiO2 (meso-TiO2) were synthesized using the sol-gel technique. A Pluronic F127 triblock-copolymer, a structure-directing agent, was incorporated as a soft template into the sol-gel. In addition, and during a separate synthesis, the sol-gel was doped with a Pt precursor. Semiconductors were prepared with 1.00wt.%, 2.50wt.%, 5.00wt.% Pt nominal loadings, respectively. They were calcined at 500°C and 550°C following synthesis. Morphological and structural properties were studied by: a) X-ray diffraction, b) UV–vis spectrophotometry, c) N2 adsorption-desorption (BET, BJH), and d) X-ray photoelectron spectroscopy (XPS). Optical band gap values for meso-TiO2 and Pt-meso-TiO2 were calculated by Kubelka-Munk (K-M) function coupled with Tauc plot methodology. It was observed that the prepared semiconductors displayed pore sizes in the 10–40nm range with bimodal distributions. Their photocatalytic activity for hydrogen production via water splitting was established in a Photo-CREC Water-II reactor under near-UV light irradiation. The aqueous solution contained 2% v/v ethanol, employed as a renewable organic scavenger. The prepared semiconductors showed that the mesoporous 2.50wt.% Pt-TiO2 has the highest photoactivity for hydrogen generation. This suggests the important role played by the loading of platinum as a TiO2 dopant, reducing the optical band gap, increasing electron storage and diminishing, as a result, electron-hole recombination. The measured Quantum Yield (QY), obtained using a rigorous approach, was established for the mesoporous 2.50wt.% Pt-TiO2 at a promising level of 22.6%.

Structure and optical properties of Er‐doped CaO‐Al2O3 (Ga2O3) glasses fabricated by aerodynamic levitation

AbstractWe fabricated a series of stable Er‐doped CaO‐Al2O3(Ga2O3) glasses by aerodynamic levitation (ADL) method. Using thermal analysis, we studied the influence of composition on the thermal stability of the glasses. The results unraveled the significance of composition on the stability of glasses. Magic angle spinning nuclear magnetic resonance (MAS‐NMR) and Raman spectra were used to analyze the glass microstructure. The optical and spectroscopic properties were examined by UV‐Vis absorption, steady‐state fluorescence spectroscopy, transient state fluorescence spectroscopy, and luminescence quantum yield measurements. The results unraveled a clear concentration‐dependent up‐conversion and NIR emissions of Er3+, with obvious spectral broadening and redshift. The related mechanisms of decrease in fluorescent lifetime (from about 9 ms to 2 ms) and quantum yield (from about 75% to 5%) are discussed.

A cost-effective quantum yield measurement setup for upconverting nanoparticles

Generally, emission quantum yield values of upconverting nanoparticles are not reported, despite its importance for characterizing the material's performance, because the measurements require quite expensive setups (a single photomultiplier operating in a broad spectral regions from the visible to the near-infrared) and laborious procedures (spectral mismatch correction when two photomultipliers are used). Here we describe the implementation of a simple and cost-effective quantum yield measurement setup using a commercial integrating sphere-based spectrometer operating in the visible spectral range and a power meter to determine the incident number of photons. First, we validate the experimental methodology using well-known down-shifting standard phosphors (sodium salicylate and perylene). Then, we use the developed setup in an illustrative example of upconverting nanoparticles, SrF2:Yb3+/Er3+(20/2%), to quantify their emission quantum yield values in powder (0.0057±0.0002 at 388Wcm−2) and water suspension (0.0028±0.0001 at 395Wcm−2).

Ingredients to TICT Formation in Donor Substituted Hemithioindigo.

Twisted intramolecular charge transfer (TICT) formation in hemithioindigo photoswitches has recently been reported and constitutes a second deexcitation pathway complementary to photoisomerization. Typically, this behavior is not found for this type of photoswitches, and it takes special geometric and electronic conditions to realize it. Here we present a systematic study that identifies the molecular preconditions leading to TICT formation in donor substituted hemithioindigo, which can thus serve as a frame of reference for other photoswitching systems. By varying the substitution pattern and providing an in-depth physical characterization including time-resolved and quantum yield measurements, we found that neither ground-state pretwisting along the rotatable single bond nor the introduction of strong push-pull character across the photoisomerizable double bond alone leads to formation of TICT states. Only the combination of both ingredients produces light-induced TICT behavior in polar solvents.

Fe(III)-functionalized carbon dots—Highly efficient photoluminescence redox catalyst for hydrogenations of olefins and decomposition of hydrogen peroxide

We present the first bottom-up approach to synthesize Fe(III)-functionalized carbon dots (CDs) from molecular precursors without the need of conventional thermal or microwave treatment and additional reagents. Specifically, sonication of xylene in the presence of anhydrous FeCl3 results in oxidative coupling of the aromatic substrate towards Fe(III)-functionalized CDs. The as-prepared CDs are spherical in shape with a size of 3–8nm, highly dispersible in organic solvents and display wavelength-dependent photoluminescence (PL). The iron ions attached to the surface endow the CDs with superior catalytic activity for olefin hydrogenation with excellent conversion and selectivity (up to 100%). The Fe(III)-CDs are more effective in the hydrogenation of a series of electron donating or withdrawing olefin substrates compared to conventional homogeneous or heterogeneous Fe(III)-based catalysts. The as-prepared heterogeneous nanocatalyst can be used repeatedly without any loss of catalytic activity. Importantly, the stability of the new catalysts can be easily monitored by PL intensity or quantum yield measurements, which certainly opens the doors for real time monitoring in a range of applications. Additionally, to the best of our knowledge, for the first time, the oxidative property of Fe-CDs was also explored in decomposition of hydrogen peroxide in water with the first order rate constant of 0.7×10−2min−1, proving the versatile catalytic properties of such hybrid systems.

Quantum Yield Measurements of Fluorophores in Lipid Bilayers Using a Plasmonic Nanocavity.

Precise knowledge of the quantum yield is important for many fluorescence-spectroscopic techniques, for example, for Förster resonance energy transfer. However, to measure it for emitters in a complex environment and at low concentrations is far from being trivial. Using a plasmonic nanocavity, we measure the absolute quantum yield value of lipid-conjugated dyes incorporated into a supported lipid bilayer. We show that for both hydrophobic and hydrophilic molecules the quantum yield of dyes inside the lipid bilayer strongly differs from its value in aqueous solution. This finding is of particular importance for all fluorescence-spectroscopic studies involving lipid bilayers, such as protein-protein or protein-lipid interactions in membranes or direct fluorescence-spectroscopic measurements of membrane physical properties.

Addition of Fluorescence Lifetime Spectroscopy to the Tool Kit Used to Study the Formation and Degradation of Luminescent Quantum Dots in Solution.

The increasing commercialization of consumer electronic products that make use of II-VI semiconductor quantum dots (QDs) has raised significant concerns about their impact on natural systems and human health once they are released into the environment at the end of the product's lifetime. In this paper, we demonstrate the addition of fluorescence lifetime spectroscopy to the existing tool kit of spectroscopic techniques to quantitatively monitor changes in QD properties as they form and degrade in solution. Our study reveals that because of its rich information content, fluorescence lifetime spectroscopy has a limited utility as a stand-alone technique in the study of QD formation and degradation. However, combining fluorescence lifetime spectroscopy with the commonly used emission quantum yield and peak width measurements along with other analytical methods, including ultraviolet-visible spectroscopy, transmission electron microscopy, and inductively coupled plasma mass spectrometry measurements, significantly enhances the existing analytical tool kit and provides the capability to monitor in real time, the formation and degradation of luminescent QDs in organic and aqueous solutions under environmentally relevant conditions.

Photooxidation of cyclohexanone in simulated atmosphere: A potential source of atmospheric formic acid

Gas phase photooxidation of cyclohexanone (CH) has been studied in the laboratory in a simulated atmospheric environment (synthetic air, 1 bar pressure) under the exposure of 311 nm UV light. Formic acid along with formaldehyde and ethylene are identified as the major photooxidation products. Quantum yield for the production of these species is measured and the values are compared with previous studies on the photo dissociation of CH. For 6 h of light irradiation with initial CH concentration of 9.19 ± 0.1 × 1016 molecules cm−3, the measured quantum yield values of ethylene and formaldehyde, the two primary photooxidation products, are 0.0395 ± 0.001 and 0.0028 ± 0.002, respectively. These values are comparable with CH dissociation quantum yield, 0.24 ± 0.02, and also the quantum yield of CO production, 0.0940 ± 0.001. The energetic parameters of different steps of the proposed reaction mechanism are calculated by electronic structure theory method at DFT/B3LYP/6–311++G** level. A reaction modeling has been performed, and similarity in simulated quantum yield values with that of the experimentally measured ones validates the suggested reaction mechanism. Experimentally measured values of rate constants of most of the elementary reaction steps incorporated in the modeling are not known, and the calculated values, obtained by use of CVT and RRKM theoretical methods are used. The total yield of formic acid, which has been assigned as a secondary oxidation product, is 3.46 ± 0.25 × 1015 molecules cm−3 as obtained from experiment and this data matches well with the value of 2.67 × 1015 molecules cm−3 obtained from reaction modeling for 6 h of UV irradiation. The yield of formic acid is comparable with the yield of primary photo products. The results imply that photooxidation of CH and analogous compounds might have significant contributions to production of formic acid in the earth's troposphere. According to the prediction of the modeling results presented here, the contribution of cyclohexanone photooxidation to the atmospheric concentration of formic acid is ∼1 pptv.

Aldoxime based biphenyl-azo derivative for self-assembly, chemosensor (Hg2+/F−) and bioimaging studies

A versatile bifunctional biphenyl-azo conjugated based aldoxime (DOXPA) was developed and its photo-responsive behaviours upon the addition of analytes has been investigated using UV–vis absorption, fluorescence emission, quantum yield and fluorescence lifetime measurements. The probe selectively recognized Hg2+ and F− over a wide range of metal ions/anions through “turn-on” fluorogenic modes. The nature of interaction between probe and Hg2+/F− has been studied using NMR titrations and DFT studies. Further, the probe has been successfully applied for intracellular sensing and imaging of Hg2+ and F−. Furthermore, we obtained sheet like morphology upon self-assembly of azo-derivative, due to the formation of hydrogen bonding between hydroxylamine. This was confirmed by Scanning Electron Microscope and Atomic Force Microscopy.

Beam-profile-compensated quantum yield measurements of upconverting nanoparticles.

The quantum yield is a critically important parameter in the development of lanthanide-based upconverting nanoparticles (UCNPs) for use as novel contrast agents in biological imaging and optical reporters in assays. The present work focuses on the influence of the beam profile in measuring the quantum yield (ϕ) of nonscattering dispersions of nonlinear upconverting probes, by establishing a relation between ϕ and excitation light power density from a rate equation analysis. A resulting 60% correction in the measured ϕ due to the beam profile utilized for excitation underlines the significance of the beam profile in such measurements, and its impact when comparing results from different setups and groups across the world.