Time-resolved Emission Spectra Research Articles

Green-emitting Bi3+-doped La2SrSc2O7 phosphor for pc-WLED lighting: Luminescent properties and energy transfer strategy

The crystal structure, photoluminescence properties, thermal stability and corresponding mechanisms of the novel Bi 3+ , Eu 3+ -doped La 2 SrSc 2 O 7 (LSS) phosphors have been measured and analyzed in details. The emission spectrum of LSS: 1.0%Bi 3+ phosphor shows a novel green emission centered at 530 nm under 340 nm excitation, which is attributed to the 3 P 1 → 1 S 0 transition of Bi 3+ ions. By designing Bi 3+ →Eu 3+ energy transfer strategy, luminescence colors of LSS: 1.0%Bi 3+ , yEu 3+ (y = 0–5.0%) phosphors can be tuned from green to orange with increasing Eu 3+ concentration, which achieve multiple emission colors in LSS host. The photoluminescence decay curves, average decay lifetimes, energy transfer efficiency and time-resolved emission spectra of LSS: 1.0%Bi 3+ , yEu 3+ (y = 0–5.0%) phosphors prove the existence of energy transfer from Bi 3+ to Eu 3+ . The prototype pc-WLED device with green-emitting LSS: 1.0%Bi 3+ possesses high color rendering index (CRI = 96.0) and low correlated color temperature (CCT = 4306 K). These results provide clear evidences that LSS: Bi 3+ and LSS: 1.0%Bi 3+ , Eu 3+ phosphors would be novel promising green-to-orange tunable phosphor candidates for pc-WLED applications. A novel green-emitting La 2 SrSc 2 O 7 : Bi 3+ phosphor and the energy transfer strategy from Bi 3+ ions to Eu 3+ ions. • A novel La 2 SrSc 2 O 7 : Bi 3+ green phosphor was synthetized by high-temperature solid-state method. • The energy transfer from Bi 3+ ions to Eu 3+ ions was designed to realize color tuning from green to orange . • The pc-WLED fabricated by LSS:Bi 3+ phosphor possesses high color rendering index and low correlated color temperature.

Laser induced breakdown spectroscopy for hydrogen detection in molybdenum at atmospheric pressure mixtures of argon and nitrogen

Present study investigated the effect of argon and nitrogen mixtures at atmospheric pressure on the hydrogen Hα line emission intensity during the Laser Induced Breakdown Spectroscopy (LIBS) measurements. LIBS is foreseen for the assessment of the fuel retention in ITER plasma facing components during the maintenance breaks when the reactor is filled with near atmospheric pressure nitrogen or dry air. The use of argon flow during LIBS measurements has shown to increase the LIBS signal at atmospheric conditions which aids the distinguishing of hydrogen isotopes. LIBS was used to ablate a small amount of molybdenum (Mo) target and the development of formed plasma plume was investigated by time-resolved emission spectra and photographs. Spectral measurements showed that the Hα line intensity and electron density decreased faster with the increased fraction of nitrogen in the background atmosphere. The electron temperature of created plasma was also lower in the nitrogen atmosphere. The spatial development of plasma plume was comparable in both argon and nitrogen atmospheres. According to these results, the reduction of Hα line intensity in the presence of nitrogen can be explained by higher fraction of energy consumption in dissociation and excitation processes of molecular gas and increased quenching of excited H states. Furthermore, the results demonstrate that a small amount of N2 impurities in Ar atmosphere does not have detrimental effect on LIBS measurements of hydrogen isotopes. Most of the local thermodynamic equilibrium (LTE) conditions required for the applicability of CF-LIBS were fulfilled in the time-window between 1-5 µs for Ar and 1-3 µs for N2 gas. One notable exception was the time-stability criterion for hydrogen atoms. The effect of this deviation from LTE on the applicability of CF-LIBS requires further studies.

Synthesis and Characterization of Far-Red Emissive Boron-Based Triads Showing Large Stokes Shifts: Optical, TRANES, and Electrochemical Studies.

Herein, we report the design and synthesis of far-red emissive boryl-thiophene-BODIPY triads 1-3. The π-conjugation length and electronic communication between borane and BODIPY moieties are tuned by judiciously varying the size of the oligothiophene spacer in these triads (1, terthiophene; 2, quarterthiophene; and 3, pentathiophene). Conjugates 1-3 showed intriguing triple emissions in the blue to far-red regions. Detailed optical, time-resolved decay kinetics, time-resolved area-normalized emission spectra (TRANES), fluoride binding, and computational studies suggest that the multiple emissions in these triads are due to an inefficient transfer of energy from the boryl-oligothiophene to the BODIPY unit. In addition, all of the conjugates showed a ratiometric fluorescence response to fluoride ions.

Temporal Dynamics of Solid-State Thermally Activated Delayed Fluorescence: Disorder or Ultraslow Solvation?

Time-resolved emission spectra of thermally activated delayed fluorescence (TADF) compounds in solid hosts demonstrate significant temporal shifts. To explain the shifts, two possible mechanisms were suggested, namely, slow solid-state solvation and conformational disorder. Here we employ solid hosts with controllable polarity for analysis of the temporal dynamics of TADF. We show that temporal fluorescence shifts are independent of the dielectric constant of the solid film; however, these shifts evidently depend on the structural parameters of both the host and the TADF dopant. A ≤50% smaller emission peak shift was observed in more rigid polymer host polystyrene than in poly(methyl methacrylate). The obtained results imply that both the host and the dopant should be as rigid as possible to minimize fluorescence instability.

Time-resolved luminescence spectroscopy of ultrafast emissions in BaGeF6

Phase-pure crystalline micropowder samples of BaGeF6 were prepared and studied under excitation by tuneable synchrotron radiation and 10 keV electron beam. Time-resolved photoluminescence emission and excitation spectra and a set of single emission decay curves were recorded at 7 K for the exciting photon energy region of 4.3–45 eV. Several intrinsic emissions were revealed in BaGeF6 and their origin investigated. A single broad emission band peaking at 455 nm is assigned to be of excitonic origin due to its long decay time in the μs range and due to the presence of an intense excitation peak at 10.1 eV right in the region of the host absorption onset. The energy gap width of BaGeF6 was determined experimentally from the photoluminescence excitation spectra of the 455 nm emission to be 10.9 eV. Several emission bands, including distinct peaks at 270 and 455 nm, with the main decay component of ∼180 ps were revealed across the wavelength range of 200–500 nm. The revealed ultrafast emissions were studied by means of time-resolved photoluminescence spectroscopy and their origin was assigned to cross-luminescence resulting from radiative transitions between the Ba 5p core level and sub-bands of the valence band (Ge 4s, Ge 4p and F 2p hybridized states) and to intraband luminescence between the valence band sub-bands. Photoluminescence excitation spectra of the ultrafast emissions revealed a gently sloping onset at 17 eV, related to transitions from the Ge 4s states. It is followed by a distinct peak at 19.4 eV, which corresponds to the ionization of the Ba 5p cation states and is related to the excitation threshold of cross-luminescence.

A time-resolved ratiometric luminescent anthrax biomarker nanosensor based on an Ir(III) complex-doped coordination polymer network.

Herein, an Ir(III) complex-doped coordination polymer network (Ir(III)@GMP-Eu3+) is fabricated for the first time for the ratiometric luminescent detection of the anthrax biomarker 2,6-dipicolinic acid (DPA) through the analysis of time-resolved emission spectra (TRES). The linear detection range is from 10 nM to 5 μM with a detection limit of 3.3 nM in aqueous solution. Attributed to the long lifetime of Ir(III)@GMP-Eu3+, the developed sensor exhibits an excellent DPA monitoring ability in a high-background solution through TRES.

Recalling the effect of fluorescence anisotropy on the measurement of quantum yields

We present a quantitative analysis of the deviations introduced by the anisotropy of the fluorescence on the measurement of the quantum yield of emission. Errors of up to 40% can be encountered depending on the characteristics of both sample and apparatus. Additionally, we have analyzed the effect of anisotropy on the study of fluorescence quenching in Stern-Volmer experiments, and on the reconstruction of time-resolved emission spectra. We conclude that the use of polarizers is recommended provided they are well characterized.

Exploration of Self-Aggregation of Coumarin 7 and Coumarin 30 in Water: Role of β-Cyclodextrin as a Modulator.

Steady-state and time-resolved spectroscopic studies demonstrate that two members of the coumarin class of dyes, coumarin 7 (C7) and coumarin 30 (C30), undergo self-aggregation in water. The development of hypsochromically shifted new absorption bands in addition to the existing monomer bands with an increase in concentration of the dyes in an aqueous medium suggests that the aggregates are of H-type. An absorption-based kinetic study reveals that the rate of aggregation of C30 is an order of magnitude faster than that of C7. Second-order rate kinetics, as obtained from the half-life (t1/2) data, implies that the aggregates are dimeric in nature. Observations of isosbestic points in area-normalized absorption spectra (ANAS) and isoemissive points in area-normalized fluorescence excitation spectra (ANFES) and time-resolved area-normalized emission spectra (TRANES) establish that ground-state monomer ⇌ dimer equilibria for both of the systems are preserved in the photoexcited state. The present study further establishes that β-cyclodextrin is the most efficient of the three common cyclodextrins in shifting the equilibria toward the monomer by encapsulating the monomers within its cavity, making β-CD a convenient modulator to control the self-aggregation process. Dynamic light scattering (DLS), quantum chemical calculations, and molecular docking studies provide further support to our propositions.

The Role of Hydrogen Bonding in the Preferential Solvation of 5-Aminoquinoline in Binary Solvent Mixtures.

5-Aminoquinoline (5AQ) has been used as a fluorescent probe of preferential solvation (PS) in binary solvent mixtures in which the nonpolar component is diethyl ether and the polar component is protic (methanol) or aprotic (acetonitrile). Hence, the roles of solvent polarity and solute-solvent hydrogen bonding have been delineated. Positive deviations of spectral shifts from a linear dependence on the concentration of the polar component, signifying PS, are markedly more pronounced in case of the protic solvent. Solvation dynamics on a nanosecond time scale mark the formation of the solvation shell around the fluorescent probe. Time-resolved area-normalized emission spectra indicate the occurrence of the continuous solvation of the excited state when the polar component is acetonitrile. In contrast, two distinct states were observed when the polar component was methanol, the second state being the hydrogen bonded one. Translational diffusion is the rate-determining step for formation of the solvation shell. The time constant associated with it has been estimated from rise times observed in fluorescence transients monitored at the red end of the fluorescence spectra and also from the time evolution of the spectral width of time-resolved emission spectra.

Collagen Glycation Detected by Its Intrinsic Fluorescence.

Collagen’s long half-life (in skin approximately 10 years) makes this protein highly susceptible to glycation and formation of the advanced glycation end products (AGEs). Accumulation of cross-linking AGEs in the skin collagen has several detrimental effects; thus, the opportunity for non-invasive monitoring of skin glycation is essential, especially for diabetic patients. In this paper, we report using the time-resolved intrinsic fluorescence of collagen as a biomarker of its glycation. Contrary to the traditional fluorescence intensity decay measurement at the arbitrarily selected excitation and detection wavelengths, we conducted systematic wavelength- and time-resolved measurements to achieve time-resolved emission spectra. Changes in the intrinsic fluorescence kinetics, caused by both collagen aggregation and glycation, have been detected.

White Light from Dual Intramolecular Charge-Transfer Emission in a Silylene-Bridged Styrylcarbazole and Pyrene Dyad

Styrylcarbazole linked to pyrene by a dimethylsilyl bridge was synthesized in the search for new charge-transfer active materials for LED applications. In the course of a photophysical study, it turned out that such a donor-bridge-acceptor compound displayed three completely different types of emission depending on solvent polarity. The most attractive emission properties were found in acetonitrile in which two broad emission bands were observed. The resolved mechanism of the excited-state processes in acetonitrile was supported by singular value decomposition with self-modeling treatment of time-resolved emission spectra (ns-TCSPC). The data analysis revealed that there were two excited-state processes, that is, charge transfer within styrylcarbazole and electron transfer from styrylcarbazole to pyrene through a silylene bridge that was responsible for a broad dual emission. The general idea of designing compounds that display emission from more than one excited state covering a wide range of the visible spectrum can be a powerful tool in designing new white-light-emitting materials.

Multinuclear Lanthanide-Implanted Tetrameric Dawson-Type Phosphotungstates with Switchable Luminescence Behaviors Induced by Fast Photochromism.

A series of benzoate-decorated lanthanide (Ln)-containing tetrameric Dawson-type phosphotungstates [N(CH3)4]6H20[{(P2W17O61)Ln(H2O)3Ln(C6H5COO)(H2O)6]}{[(P2W17O61)Ln(H2O)3}]2Cl2·98H2O [Ln = Sm (1), Eu (2), and Gd (3)] were made using a facile one-step assembly strategy and characterized by several techniques. Notably, the Ln-containing tetrameric Dawson-type polyoxoanions [{(P2W17O61)Ln(H2O)3Ln(C6H5COO)(H2O)6]}{[(P2W17O61)Ln(H2O)3}]224- are all established by four monolacunary Dawson-type [P2W17O61]10- segments, encapsulating a Ln3+ ion with two benzoates coordinating to the Ln3+ ions. 1-3 exhibit reversible photochromism, which can change from intrinsic white to blue for 6 min upon UV irradiation, and their colors gradually recover for 30 h in the dark. The solid-state photoluminescence spectra of 1 and 2 display characteristic emissions of Ln components based on 4f-4f transitions. Time-resolved emission spectra of 1 and 2 were also measured to authenticate the energy transfer from the phosphotungstate and organic chromophores to Eu3+. In particular, 1 shows an effectively switchable luminescence behavior induced by its fast photochromism.

Detecting beta-amyloid glycation by intrinsic fluorescence - Understanding the link between diabetes and Alzheimer's disease

We monitor early stages of beta-amyloid (Aβ1–40) aggregation, one of the key processes leading to Alzheimer's disease (AD), in the presence of high glucose concentrations by measuring Aβ1– 40 intrinsic fluorescence. The multiple peaks and their shifts observed in the time-resolved emission spectra (TRES) reveal the impact of glycation on Aβ1– 40 oligomerisation. The results show that formation of the advanced glycation end products (AGEs) alters the aggregation pathway. These changes are highly relevant to our understanding of the pathophysiology of AD and the implication of AGE and diabetes in these pathways.

Time-resolved and excitation-emission matrix luminescence behaviour of boro-silicate glasses doped with Eu3+ ions for red luminescent application

This paper reports the time-resolved luminescence and excitation-emission matrix (EEM) measurements of three different boro-silicate host glasses doped with Eu3+. The effect of zinc and tellurium oxide addition on the photoluminescence (PL) and time-resolved emission spectra (TRES) of the glasses was also studied. At 392 nm of excitation wavelength, a bright red electric dipole (ED) transition 5D0 → 7F2 (615 nm) and a weak orange magnetic dipole (MD) transition 5D0 → 7F1 (590 nm) were observed. The asymmetric ratio (ED/MD) values were increased in the order Eu < Eu-Zn < Eu-Te. The decay associated spectra (DAS) showed a bright red emission transition (5D0 → 7F2) at 612 nm for all glasses. The time-resolved analysis revealed that, because of the glass network randomness, the luminescence emissions did not present the same lifetime or wavelength for the same transition bands, attributed to different environments (or interactions) experienced by Eu3+ ions in the glass network.

Nature of Saccharide-Induced F127 Micellar Dehydration: An Insight with FDAPT (2-Formyl-5-(4'-N,N-dimethylaminophenyl)thiophene), a Multiparametric Fluorescent Probe.

FDAPT (2-formyl-5-(4'-N,N-dimethylaminophenyl)thiophene) is an efficient environment-sensitive fluorescent probe, which senses the alteration of its microenvironment with six different fluorescent parameters, namely, emission intensity, wavelength, fluorescence anisotropy, and corresponding three time-dependent parameters fluorescence lifetime, time-resolved emission spectrum, and anisotropy decay. In the present work, the nature of saccharide-induced dehydration of a F127 polymeric micelle is investigated in detail with FDAPT emission. Using a multiparametric fluorescence approach, it is observed that the saccharide molecules not only decrease the critical micellization temperature of the F127 solution but also strongly alter the physical properties inside the micellar structures. The local polarity and fluidity significantly decrease in the saccharide-induced micelle as compared to the normal F127 micelle. The probe solvation dynamics study reveals that the water content in the core as well as corona domain diminishes significantly in the saccharide-induced micelle as compared to the normal micelle. More precisely, dehydration occurs more in the core region than in the corona region. Also, the saccharide-induced dehydration alters the relative size of the core and corona regions. The extent of dehydration varies with different saccharide molecules. It is also found that the dehydration efficiency order is trisaccharide (raffinose) > disaccharide (sucrose) > monosaccharide (glucose and fructose).

Combining Dual-Light Emissions to Achieve Efficient Broadband Yellowish-Green Luminescence in One-Dimensional Hybrid Lead Halides.

In recent years, low-dimensional lead halides have emerged as some of most attractive photoelectric materials due to their intrinsic broadband emissions with a potential application in white-light emitting diodes. To achieve the desired performance, tremendous research has emphasized the modulation of inorganic components as optical centers; however, less work has paid attention to the direct contribution of the organic components. Herein, we successfully assembled two new hybrid lead halides of [H2BPP]Pb2X6 (X = Br, 1, and Cl, 2) containing one-dimensional double [Pb2X6]2- chains using optically active 1,3-bis(4-pyridyl)-propane (BPP) as an organic cation. Under UV-light excitation, compounds 1 and 2 exhibit broadband yellowish-green emissions, which were verified by promising photoluminescence quantum efficiencies (PLQEs) of 8.10% and 4.84%, respectively. The broadband light emissions are derived from the combination of dual higher-energy blue and lower-energy yellow light spectra, which can be attributed to the individual contributions of the organic and inorganic components, respectively, according to the time-resolved and temperature-dependent emission spectra as well as theoretical calculations. This work proves the great contribution of organic components to the photophysical properties and provides a new design strategy to realize broadband light emission by rationally combining the dual-emitting properties of different assembly blocks.

Photoluminescence and afterglow tuning in ultra-broadband near-infrared Mg3Y2Ge3O12:Cr3+ phosphor via cation substitution

Broadband near-infrared (NIR) long-persistent phosphors with adjustable optical property have been urgently demanded for practical applications in bio-imaging and plant cultivation. Herein, Cr3+ doped Mg3Y2Ge3O12 garnet phosphors with ultra-broadband NIR emissions (600−1200 nm) peaked at 776 nm were prepared via a high-temperature solid-state reaction method, and the cation sites for Cr3+ were well identified and assigned based on the Rietveld refinement and time-resolved emission spectra (TRES). Under the excitation at 436 nm, wide-range modulations in intensity, wavelength (763−834 nm) and bandwidth (143−227 nm) of 4T2→4A2 (4F) transition were achieved via Zn2+/Ca2+ substitution, which completely covers the maximum absorption ranges (715−1050 nm) of bacteriochlorophyll from anaerobic photosynthetic bacteria (PSB). According to the classic Tanabe-Sugano theory, the crystal field parameters around different Cr3+ centers were calculated to explain the spectral tailoring effect. Meanwhile, the afterglow duration was greatly improved from 2 min to 66 and 240 min after co-doping Zn2+/Ca2+, and the trap distribution and mechanism was elaborately explored via thermos-luminescence (TL) experiments. Above results provide an effective strategy for designing NIR-emitting phosphors with desired optical and afterglow performance, which well meets the light requirements of diverse applications especially in plant growth.

Acid–base reaction of a cationic hydration probe in vicinity of anionic interface of AOT reverse micelles

The excited-state proton transfer (ESPT) of a cationic super-photoacid, N-methyl-7-hydroxyquinolium, has been studied within the water pool of an aerosol-OT reverse micelle (RM). Time-resolved emission spectra were obtained and analyzed to reveal the effect of environmental heterogeneity on the ESPT process. The ESPT was found to involve two main emissive species, namely the excited cationic and keto forms of the photoacid and was facilitated by scenarios that expose them to an abundance of water molecules. The dynamic charge-state transition (from positive to neutral) induced by the ESPT dictated the location and diffusion of the probe with the modulation of the Coulombic interaction between the probe and anionic interface of the RM. The non-exponential behavior of the ESPT was observed using time-resolved intensity profiles and rationalized in terms of the heterogeneity along the reaction coordinates involving the hydrogen-bond network, polarity, and viscosity of the confined water pool within the RM. It was found that the disruption of the hydrogen-bond network in the vicinity of the interface resulted in the decrease of polarity that retarded the overall ESPT by modulating the energetics of the reactant and the product in the ESPT. Solvation dynamics was also considered and found to occur on timescales faster than the ESPT process, profoundly for larger water pools.

Color tuning from green to orange-red in SrBPO5: UO22+/Pr3+ phosphor via energy transfer for solid-state lighting applications

SrBPO5 doped with Pr3+, UO22+, Pr3+ and UO22+ were prepared through the conventional solid-state reaction route. PXRD and Raman spectroscopy studies confirmed the phase purity of these synthesized phosphors. The particle shape, size and distribution of dopants were studied using SEM and EDX. DFT calculations were carried out to check the suitability of the SrBPO5 host for the phosphor applications. The optical bandgap of the phosphors was obtained from the recorded diffuse reflectance spectra. The orange-red emission of Pr3+ got enhanced significantly in the presence of UO22+ codopant due to energy transfer from UO22+ to Pr3+. Interestingly, the UO22+ codoping resulted in Stark splitting of Pr3+ emission. The lifetime decay measurements confirmed the energy transfer and the Time-resolved emission spectra suggested dual-site occupancy of the uranyl ion in the SrBPO5 host.

Dynamics of electron transfer in melanin-trinitrofluorenone system

The kinetics of photoluminescence (PL) and time-resolved emission spectra (TRES) of melanin solutions with an effective electron acceptor 2,4,7-trinitrofluorenone (TNF) have been studied. Based on the analysis of the kinetic decay curves and TRES, the fast and slow PL decay components can be distinguished, which characterize the processes of a relaxation of excited states and charge transfer in the melanin-TNF molecular system. In this paper, the observed dependences have been analyzed and the model to explain such behavior of PL dynamic characteristics has been proposed.