Initial Emission Intensity Research Articles

Synthesis and tunable blue–green color emission and energy transfer of Ce3+, Tb3+ co-doped BaZrSi3O9 phosphors

Utilizing energy transfer process, Ce3+, Tb3+ co-doped BaZrSi3O9 (BZS) phosphors have been successfully prepared via solid state reaction process. The phase structure, photoluminescence properties, decay curves, thermal stability, and the energy transfer mechanism were investigated in this paper. The critical distance calculated by quenching concentration method was 8.84 A, and the energy transfer process from Ce3+ to Tb3+ in BZS:Ce3+/Tb3+ phosphors had been demonstrated to be a resonant type via a dipole–quadrupole mechanism. The emission colors of the phosphors could be tuned from blue (0.1625, 0.1261) to green (0.2979, 0.5473) through the corresponding Ce3+ to Tb3+ energy transfer. Moreover, thermal quenching luminescence results revealed that BZS:Ce3+, Tb3+ exhibited good thermal stability. The Tb3+ intensity of BZS:0.04Ce3+, 0.02Tb3+ sample showed about 60.88 % of its initial emission intensity at room temperature. The above results indicate that the phosphors may be potentially used as single-component blue–green emission phosphors for application in light emitting device.

Stable and efficient colour enrichment powders of nonpolar nanocrystals in LiCl.

In this work, we propose and develop the inorganic salt encapsulation of semiconductor nanocrystal (NC) dispersion in a nonpolar phase to make a highly stable and highly efficient colour converting powder for colour enrichment in light-emitting diode backlighting. Here the wrapping of the as-synthesized green-emitting CdSe/CdZnSeS/ZnS nanocrystals into a salt matrix without ligand exchange is uniquely enabled by using a LiCl ionic host dissolved in tetrahydrofuran (THF), which simultaneously disperses these nonpolar nanocrystals. We studied the emission stability of the solid films prepared using NCs with and without LiCl encapsulation on blue LEDs driven at high current levels. The encapsulated NC powder in epoxy preserved 95.5% of the initial emission intensity and stabilized at this level while the emission intensity of NCs without salt encapsulation continuously decreased to 34.7% of its initial value after 96 h of operation. In addition, we investigated the effect of ionic salt encapsulation on the quantum efficiency of nonpolar NCs and found the quantum efficiency of the NCs-in-LiCl to be 75.1% while that of the NCs in dispersion was 73.0% and that in a film without LiCl encapsulation was 67.9%. We believe that such ionic salt encapsulated powders of nonpolar NCs presented here will find ubiquitous use for colour enrichment in display backlighting.

Observation of “fast” and “slow” decay processes in oxygen-doped hydrogenated amorphous silicon nitride thin films

Oxygen-doped amorphous silicon nitride thin films were fabricated in a plasma enhanced chemical vapor deposition system by using H2 diluted gases under a substrate temperature of 250 °C. An intense photoluminescence was achieved under 325 nm laser excitation and the luminescence is reduced to about 70% of the initial emission intensity after 1hr laser irradiation, which is improved compared with that deposited at low substrate temperature. Time-resolved photoluminescence behaviors were characterized and two recombination processes were observed, one is a “fast” nanosecond PL decay component which was explained in terms of the relaxation process to the localized O-Si-N related states, and the other is a “slow” microsecond radiative recombination component via the localized states associated with O-Si-N bands.

The pure-phase Ba3−xCaxSi6O12N2:Eu2+green phosphor: synthesis, photoluminescence and thermal properties

The promising green oxynitride phosphor, Ba3−xCaxSi6O12N2:Eu2+, was synthesized at 1350 °C for 5 hours under a reducing N2/H2 (5%) atmosphere via the solid-state reaction method. The XRD patterns confirm the formation of the pure phase of Ba3−xCaxSi6O12N2:Eu2+. With an increase in x, the emission spectra shift from 525 nm to 536 nm under near-UV (n-UV) excitation. Accordingly, we propose the underlying mechanisms for the red-shift of the emission spectra by adjusting the cation composition in the host. The influence of the size mismatch on the thermal quenching is also observed. The as-prepared green phosphor exhibits great thermal quenching property, with the remaining 83% of the initial emission intensity measured at 150 °C. The quantum efficiency is measured to be 35.2%. All the results indicate that the Ba3−xCaxSi6O12N2:Eu2+ can be a good candidate phosphor applicable to n-UV light-emitting diodes for solid-state lighting.

A novel white emitting phosphor of Dy3+ doped Ca19Mg2(PO4)14 for light-emitting diodes

A series of Dy3+ doped Ca19Mg2(PO4)14 phosphors were firstly synthesized by the solid-state reaction method. The phase purity and characteristic luminescent properties are investigated in detail by X-ray diffraction refinement, photoluminescence spectra and decay times measurement. Under 365nm excitation, Ca19Mg2(PO4)14:Dy3+ phosphor can exhibit intense warm white emission with CIE chromaticity coordinates (0.400, 0.452) and low correlated color temperature (3994K). The optimal doping contents of Dy3+ in Ca19Mg2(PO4)14 is determined to be 2%. The thermal quenching property of Ca19Mg2(PO4)14:Dy3+ is also investigated and it remains 60% of the initial emission intensity even when the temperature increases to 230°C. The results show that Ca19Mg2(PO4)14:Dy3+ can be a promising single phased white emitting phosphor for UV white LEDs.

Conjugated Poly(fluorene-quinoxaline) for Fluorescence Imaging and Chemical Detection of Nerve Agents with Its Paper-Based Strip

Conjugated polymer of poly(fluorene-co-quinoxaline) was synthesized via Suzuki coupling polymerization. The emission color of the polymer can be tuned depending on the concentration of the polymer in solution. A low-energy bandgap is observed both in the concentrated solution and in the solid state, caused by aggregation of the polymer chains, resulting in long wavelength emission from the quinoxaline moiety, while short wavelength emission can be seen in diluted, well-dissolved solution. The presence of quinoxaline units enables us to demonstrate fluorescence switching and imaging. Paper-based strips containing the polymer are prepared via simple immersion of filter paper in the polymer solution for practical use in the detection of nerve agents. The emission of the paper-based strip is quenched upon exposure to diethyl chlorophosphate (DCP), a nerve agent simulant, and the initial emission intensity can be almost restored by treatment with aqueous sodium hydroxide solution, making a possible reversible paper-based sensor.

Interaction of CdSe/ZnS quantum dots with the marine diatom Phaeodactylum tricornutum and the green alga Dunaliella tertiolecta: A biophysical approach

In this study, we investigated the interaction of nanoparticles, such as CdSe/ZnS quantum dots (QDs), with the marine diatom Phaeodactylum tricornutum and the green alga Dunaliella tertiolecta, as biological models in the marine environment. Fluorescence kinetics measurements indicated that 30min after dispersion in seawater QDs lost the 60% of the initial emission intensity, possibly due to the occurrence of aggregation processes. However, the presence of algae seemed to mitigate this effect. By using confocal microscopy, we highlighted the presence of QDs adsorbed on the surface of both algae, but not inside the cells. The toxicity of QDs was evaluated in terms of inhibition of growth rate, oxidative stress, and lipid peroxidation. QDs in the range of 1–2.5nM gradually inhibited the growth rate of P. tricornutum and increased the oxidative stress, as evinced by the increase in lipid peroxidation, reactive oxygen species (ROS) production and activity of two main antioxidant enzymes (superoxide dismutase and catalase). On the contrary, QDs did not inhibit the growth rate of D. tertiolecta, at most a modest stimulation was observed in the range of 0.5–2nM, suggesting a hormetic response. No effect in the parameters indicating oxidative stress was observed in the green alga. In conclusion our results showed that the biological effects were species-specific.

Luminescence properties of Ho3+ co-doped SrAl2O4:Eu2+, Dy3+ long-persistent phosphors synthesized with a solid-state method

In this study our aim was partially substituting or replacing Dy3+ co-dopant ions in SrAl2O4:Eu2+, Dy3+ phosphors with less expensive Ho3+ co-dopant ions in order to open a more economical way towards the industrial scale synthesis of long-persistent strontium-aluminate phosphors while maintaining the good optical properties of Dy3+ co-doped phosphors. This was achieved by finding the optimum ratio between the Dy3+ and Ho3+ co-dopants to get the highest initial intensity and by compensating the fast decay speed caused by Ho3+ co-doping via defect site generation in the host through non-stochiometric Sr/Al ratios.The initial emission intensity was the highest when the co-activator was substituted entirely with Ho3+ ions, and even the phosphors containing mixed co-activators featured higher initial emission intensities than the reference Dy3+ co-doped samples. However, the samples co-activated with Ho3+ or mixed co-activators exhibited faster decay speeds relative to the Dy3+ co-activated samples. This negative effect could be compensated by increasing the relative amount of aluminum in the phosphor.

Homogeneous immunoassays based on fluorescence emission intensity variations of zinc selenide quantum dot sensors

The fluorescence emission intensity of ZnSe quantum dots (QDs) conjugated to proteins to form QD-based biomolecular sensors increases significantly upon binding of the sensors to target proteins in solution. This phenomenon enables the development of homogeneous, separation-free immunoassays for rapid quantitative detection of proteins in solution. Proof-of-principle assays were developed by dosing a solution containing a biomolecular target with a solution containing the corresponding QD-based sensor and monitoring the changes in the peak fluorescence emission intensity of the QDs. Direct immunoassays for detecting basic fibroblast growth factor (bFGF) and prostate-specific antigen (PSA) in solution were demonstrated using QD-anti-bFGF and QD-anti-PSA sensors. A competitive immunoassay for detecting human serum albumin (HSA) was also demonstrated by dosing samples containing HSA with QD-HSA sensors and free anti-HSA antibodies. The QD-HSA sensors were tested in 1000× diluted human serum and found to be unaffected by interference from other proteins. The lower limit of detection of the assays was equal to the lowest sensor concentration in the solution that can be unambiguously detected, typically less than 1nM. The dynamic range of the assays was determined by identifying the sensor concentration above which optical interference between QDs affected adversely the observed fluorescence emission intensity. The upper limit of this concentration was 2.5μM for 4nm QDs. The ZnSe QD-based sensors were stable and preserved ∼80% of their initial peak emission intensity after two months in refrigerated storage. These biosensors have potential applications in rapid sensing of target proteins for emergency and point-of-care diagnostic applications.

Role of oxidative pre-calcination in extending blue emission of Sr4Al14O25 nanophosphors formed with microemulsions

Here, we report the preparation of a single phase blue emitting long persistence Sr4Al14O25 nanophosphors formed in the presence of 5mol% boric acid at 1100°C when oxidative pre-calcination was applied to precursors synthesised within microemulsions. This two stage process allowed homogeneous dopant distribution and efficient substitutional incorporation of BO4 in the aluminate framework, which generated associated defect states providing deep trap levels responsible for long persistence, now confirming the previously proposed mechanisms. In addition, the formation of glassy borate phases were avoided reducing aggregation which resulted in crystallite sizes that spanned 41–52nm and particle sizes in the range 50–200nm. This two stage process with calcination at 1100°C resulted in increased initial emission intensity (12%) as well as enhanced long persistence, with a lifetime of deep trap states (τ3) of 850s compared to the range 470–690s from conventional one stage reductive calcination.

Self-Assembly of Metallamacrocycles Using a Dinuclear Organometallic Acceptor: Synthesis, Characterization, and Sensing Study

A dinuclear organometallic acceptor 4,4'-bis[trans-Pt(PEt(3))(2)(O(3)SCF(3))(ethynyl)]biphenyl (1) containing Pt-ethynyl functionality is synthesized. Multinuclear NMR ((1)H, (31)P, and (13)C), infrared (IR), and electrospray ionization mass spectrometry (ESI-MS) including single-crystal X-ray diffraction analysis established the formation of 1. Equimolar treatment of acceptor 1 separately with three different "clip" type ditopic donors (L(a)-L(c)) yielded [2 + 2] self-assembled three metallamacrocycles 2a-2c, respectively. These macrocycles were characterized by various spectroscopic techniques, and their sizes/shapes were obtained through geometry optimization using molecular mechanics universal force field (MMUFF) simulations. Attachment of unsaturated ethynyl functionality to biphenyl building unit helped to make the macrocycles (2a-2c) π-electron rich and thereby fluorescent in nature. Furthermore, 2c in solution has been examined to be suitable for sensing electron-deficient nitroaromatic like picric acid, which is often considered as a secondary chemical explosive. The fluorescence study of 2c showed a marked quenching of initial emission intensity upon titrating with picric acid (PA), and it exhibited the largest fluorescence quenching response with high selectivity among various other electron deficient aromatic compounds tested.

Photoswitchable Fluorescent Assemblies Based on Hydrophilic BODIPY−Spiropyran Conjugates

In search of strategies to design photoswitchable fluorescent probes and operate them in aqueous environments, we have envisioned the possibility of incorporating fluorescent, photochromic, and hydrophilic components within the same macromolecular construct. First, we synthesized a fluorophore−photochrome dyad, pairing a BODIPY fluorophore and a spiropyran photochrome in its molecular skeleton, and investigated the photochemical and photophysical properties of this compound in acetonitrile. Under these conditions, the photoinduced isomerization of the spiropyran causes a 56% decrease in the emission intensity of the BODIPY at the photostationary state. The photogenerated isomer has a lifetime of 2.7 × 102 s and reverts thermally to the original form, restoring the initial emission intensity. On the basis of these results, we copolymerized a similar BODIPY−spiropyran conjugate with a monomer bearing a pendant polyethylene glycol chain. The resulting polymer is soluble in aqueous environments, and its fluor...

Protection of organic light-emitting diodes over 50 000 hours by Cat-CVD SiN x/SiO xN y stacked thin films

Silicon oxynitride (SiO x N y ) films have been formed by adding proper amount of oxygen gas to usual forming condition of silicon nitride (SiN x ) films in catalytic chemical vapor deposition (Cat-CVD) method. The composition and refractive index of the film can be systematically controlled by changing oxygen flow rate. Organic light-emitting diodes (OLEDs) covered with SiN x /SiO x N y stacked films have been completely protected from damage due to oxygen and moisture and their initial emission intensity is maintained over 1000 hours under 60 °C and 90% RH, which is equivalent to 50 000 hours in normal temperature and humidity conditions.

Chemiluminescence of isotactic polypropylene induced by photo‐oxidative degradation and natural weathering

AbstractThe analysis of the chemiluminescence (CL) kinetic parameters (induction time, oxidation rate, and activation energy) after the UV irradiation and outdoor exposure of isotactic polypropylene (i‐PP) films have been studied. The initial CL emission intensity increased with increasing photodegradation time of i‐PP films. On photodegradation, the activation energies were found to decrease linearly with time of UV‐irradiation and outdoor exposure. The slopes of these linear dependences were used to indicate the degree of photodegradation of the polymer and also for the characterization of the stabilizing effect of the additive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4623–4629, 2006

Estimation of background continuum emission intensity of inductively coupled plasma for correction of fast changing background

A method to estimate background continuum emission in inductively coupled plasma-atomic emission spectrometry (ICP-AES) is proposed. The method assumes that the ICP background continuum emission is mainly due to recombinative radiation in the plasma. The emission intensity at an arbitrary wavelength is related to the temperature and electron number density of the plasma. Furthermore, the ratio of background continuum emission intensity at two arbitrary plasma excitation conditions is a constant for all wavelengths. Therefore, if there is a change in plasma excitation conditions, the new background continuum emission intensity at an arbitrary wavelength can be calculated from the initial background emission intensity and the emission intensity ratio that can be measured accurately at another convenient wavelength. In this paper, rather than the emission intensity ratio, the ratio of the differences in intensities is used to remove the contribution of dark current in the measured intensity, if any. The ratio is termed ‘ f-factor’. Firstly, the background emission intensities at two reference plasma excitation conditions are measured. The f-factors of these two background emission intensities are assigned values 0 and 1, respectively. When the plasma excitation condition changes, the f-factor relative to the reference conditions at an arbitrary wavelength can be calculated from the new emission intensity. The background emission intensity at other wavelengths can then be determined from their corresponding emission intensities at the reference conditions and the new f-factor. Background emission intensity of the ICP (λ=200–460 nm) is measured using an ICP spectrometer with a segmented-array imaging detector. The ICP forward power was varied from 800 to 1500 W. In agreement of the model, the f-factors at any wavelengths remain constant at all forward power used. The proposed method was compared to off-peak background correction method. Analyte concentrations were selected to give signal-to-background ratio of ∼1. The corrected analyte emission intensities using both background correction methods agree, except for Ca 396.847 nm, which suffers from spectral overlap from a nearby hydrogen emission line. The ability of the proposed method for background correction of fast changing background emission was demonstrated using direct sample insertion and a direct reading multi-channel spectrometer.

Initial peak on the time dependence of the heterogeneous recombination velocity of hydrogen atoms at the surface of phosphor crystals

The radical recombination luminescence of phosphor crystals in strong atomic fluxes was investigated. An initial emission intensity peak was observed whose amplitude depends on the magnitude of the atomic flux, the phosphor crystal temperature, and the interval between switching the atomic source off and on.

A NEW REDUCING AGENT OF FLAVINS AND ITS APPLICATION TO THE ASSAY OF BACTERIAL LUCIFERASE

Copper(I) plus ethylenediaminetetraacetic acid, Cu(I)-EDTA, reduces flavins. Using Cu(I)-EDTA reduction of riboflavin 5'-phosphate, a new assay method for bacterial luciferase is established. In previous assay methods, flavin and aldehyde substrates for luciferase have been routinely added to luciferase at different times; the new assay permits aldehyde and Cu(I)-reduced flavin to be injected simultaneously into air-saturated buffer containing luciferase. In the new assay method using Cu(I), bovine serum albumin is not required, the initial emission intensity is more than twice and the overall yield is about twice of that in the so-called standard assay for luciferase.

Retardation of immunofluorescence fading during microscopy.

Polyvinyl alcohol (PVA) mounting medium containing paraphenylenediamine (PPD), n-propyl gallate (NPG), or 1,4-diazobicyclo(2,2,2)-octane (DABCO) was compared with PVA alone or buffered glycerol with regard to capacity for preservation of immunofluorescence preparations. The results were based on staining of an artificial substrate with homogeneous antigen distribution followed by microphotometric determination of the initial light emission from bound fluorescein isothiocyanate (FITC)-labeled antibody and the subsequent fluorescence fading during 3-min exposure to blue excitation light. At a concentration of 0.2-2.0 g/liter and 6 g/liter, respectively, PPD and NPG were shown to effectively retard fluorescence fading without notably decreasing the initial emission intensity; two requisites were that the modified PVA used must be rather fresh and that the mounted preparations be examined within a few days. Although addition of DABCO (6 g/liter) afforded a mounting medium that tolerated storage before use better, but both PPD and NPG were more advantageous in practice. The retarding effect of PPD on fading of FITC emission was confirmed by performance testing on human tissue sections. Remounting in PVA alone is recommended for prolonged storage of sections that have been mounted in PVA modified with one of the above-mentioned compounds.

Photostimulated Exoelectron Emission from Quenched Metals

The effect of quenching temperature on the initial intensity and on the temperature dependence of photostimulated EEE from quenched metals has been investigated. The initial emission intensity increases with increasing concentration of non equilibrium vacancies. Vacancy migration energies in investigated metals have been determined by analysing the profile of the maxima on the temperature dependence of the emission intensity.

Quenching of fluorescence from Ru(dipy)2+3 and Ru(dipy)2(CN)2 in solutions of sodium dodecyl sulphate

The kinetics of the fluorescence quenching of Ru(dipy)2+3 and Ru(dipy)3(CN)2 by Cu2+ and MV2+ are reported. At SDS concentrations above the c.m.c. the kinetics of Ru(dipy)2+3 quenching by both quenchers are simple first order with constants which increase linearly with quencher concentration and which decrease with increasing SDS concentration. The results quantitatively agree with those predicted by the model in which the emitter is completely micellised and the quenching is slow enough to allow equilibration of the quencher between solution and micelles. With Ru(dipy)2(CN)2 above the c.m.c., the quenching by MV2+ has fast and slow components, the latter being that of the natural emission decay. The results are shown to be consistent with almost complete micellisation of the quencher and a high micellar quenching rate constant. With Cu2+ the micellar quenching is too fast to follow so that ‘quasi-static quenching’ is seen, i.e. there is a decrease in the initial emission intensity followed by the slower unquenched decay. However, analysis shows that specific interaction of Cu2+ with the emitter on the micelle must be assumed to account for the abnormally high efficiency of Cu2+.Enhanced quenching of Ru(dipy)2+3 emission by Cu2+ and MV2+ is also observed below the c.m.c. This is explained in terms of the formation of clusters of the emitter and SDS with which the quenchers associate. With Ru(dipy)2(CN)2 only Cu2+ gives enhanced quenching below the c.m.c. It is suggested that Cu2+ complexes with SDS to form a micelle-like species with which the emitter can associate.