Time-resolved Luminescence Spectra Research Articles

Oxygen sensing performance modulation using luminescent ionic copper iodide clusters based on Mn(Ⅱ) crystal field intensity

Copper iodide (CuI) clusters have continued been to arouse increasing attention in many fields due to their high cost-performance, abundant reserves, hypotoxicity and structural diversity. Despite the oxygen sensing capability of coordinate CuI clusters has been demonstrated, the ionic counterparts with better structural stability hold potential to construct more durable sensing platform. However, the optical applications of the ionic CuI clusters have been hindered largely by their prominently weak emission. With the progress of ion assembly in recent years, ionic CuI clusters with specific emission properties can be attainable. Herein, two ionic dinuclear CuI clusters with Mn(Ⅱ) crystal field are introduced through fabricating sensing films to exhibit their oxygen sensing performance for the first time. The results reveal that both sensing films presented good reversibility, fast response associated with wide linear responses in the range from 0 % to 90 % gaseous O2. When the sensing behaviors of the two clusters were compared, different I0/I100 ratios of 6.6 and 2.1 are observed. Through investigating EPR spectra and time-resolved luminescence spectra, we highlight that different Mn(Ⅱ) crystal field intensity in corresponding clusters lead to distinct oxygen sensing behaviors. In our perception, the possible mechanism could offer new performance modulation strategy based on CuI clusters with multi-emission centers. Owing to the good structural stability of such materials, one of the clusters is used to demonstrate the dissolved oxygen sensing capability of the platform. The study constructs a stable sensing system and will pave the new way for optical application of the family of ionic CuI clusters.

Oxygen sensing behavior modulation of tetranuclear copper iodide hybrid materials using ligand engineering

Copper iodide hybrid materials (CIHMs) are receiving great attention as promising luminescent materials. Their structural diversity can be enriched by design and selection of organic ligands, associated with corresponding photophysical properties. However, the role of ligands in modulating sensing performance of CIHMs stays rarely revealed. Here, we demonstrate the O2 sensing capability of four tetranuclear CIHMs and reveal the impact of ligands on their different triplet quenching process. Oxygen sensing films were prepared using the selected CIHMs. The study results reveal their oxygen sensing behaviors with wide linear photoluminescence (PL) responses in the range from 0% to 100% for gaseous oxygen, and the corresponding PL quenching ratios of 12.14, 11.30, 2.90 and 2.26 (0–100% O2), respectively. In addition, all the CIHMs showed rapid and reversible response to oxygen within 10 s. Through investigating the time-resolved luminescence spectra, 1H NMR and corresponding crystal structures of the CIHMs in N2 and O2 environments, we highlight that specific crystal stacking patterns caused by different ligands play a major role in their distinct oxygen sensing behaviors. It indicates that the sensing performance of the CIHMs can be regulated through functionalization of the ligands which inspires new insights into their more extensive application.

Study on luminescent performance of Dy3+-, Tb3+-doped and Tb3+/Dy3+ co-doped TeO2-(Gd,Lu)2O3-WO3 glass scintillators

Three series of Dy3+-, Tb3+-doped and Tb3+/Dy3+ co-doped 40TeO2-20(Gd,Lu)2O3–40WO3 glasses with density of about 6.75 g/cm3 were successfully prepared by high temperature melt-quenching method. The luminescence properties of these rare earth ions doped 40TeO2-20(Gd,Lu)2O3–40WO3 glass were systematically studied by transmittance, photoluminescence (excitation and emission spectra), time-resolved emission spectra (TRES) and X-ray excited luminescence (XEL) spectra, together with the luminescence decay curves. The optimal doping concentration of Dy3+ and Tb3+ ions in 40TeO2-20(Gd,Lu)2O3–40WO3 glasses was determined under UV and X-ray excitation, respectively. It is found there is an efficient energy transfer from Dy3+ to Tb3+ ions in 40TeO2-20(Gd,Lu)2O3–40WO3 glass in photoluminescence spectra. However, it is not true under X-ray excitation due to the complicated physical process.

Unusual Effect of Minor Change in Ligand Substitution in Modulation of NIR Emission: A Case Study with [L-ZnII-LnIII] Complexes.

There have been numerous instances of lanthanide NIR emitting material where one or more types of ligands or metal ion-ligand complexes operate as antennas. The antenna's role in NIR emission has also been thoroughly investigated and validated. The emission properties of the different antennae are predicted to differ. Here we describe the structural and photophysical properties of two series of [ZnII-LnIII] complexes, where a minor difference between the two series (ethoxy vs methoxy substitution) affected the photophysical properties, particularly the f-f transition, in an unprecedented manner. Both steady-state and time-resolved luminescence spectra were affected by this change. Detailed single-crystal X-ray diffraction (SCXRD) and X-ray photoelectron spectroscopy (XPS) studies of both complexes revealed the crucial structural differences in crystal packing, which astonishingly remains unaffected in solution.

Influence of the First Coordination of Uranyl on Its Luminescence Properties: A Study of Uranyl Binitrate with N,N-Dialkyl Amide DEHiBA and Water.

Uranyl binitrate complexes have a particular interest in the nuclear industry, especially in the reprocessing of spent nuclear fuel. The modified PUREX extraction process is designed to extract U(VI) in the form of UO2(NO3)2(L)2 as has been confirmed by extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD), and time-resolved laser-induced fluorescence spectroscopy (TRLFS) measurements. In this study, the L ligands are two molecules of N,N-di-(ethyl-2-hexyl)isobutyramide (DEHiBA) monoamide used to bind uranyl in its first coordination sphere. DEHiBA ligands can coordinate uranyl in either trans- or cis-position with respect to the nitrate ligands, and these two conformers may coexist in solution. To use luminescence spectroscopy as a speciation technique, it is important to determine whether or not these conformers can be discriminated by their spectroscopic properties. To answer this question, the spectra of trans- and cis-UO2(NO3)2(DEiBA)2 conformers were modeled with ab initio methods and compared to the experimental time-resolved luminescence spectra on UO2(NO3)2(DEHiBA)2 systems. Moreover, the hydrated uranyl binitrate UO2(NO3)2(H2O)2 complexes in the same trans and cis configurations were modeled to quantify the impact of organic DEHiBA on the luminescence properties.

Time-resolved luminescence spectra of greater celandine plant extract (Chelidonium majus L.)

Time-resolved luminescence spectra of greater celandine plant extract (Chelidonium majus L.)

Photophysical and Chiroptical Properties of the Enantiomers of N,N'-Bis(1-phenylpropyl)-2,6-pyridinecarboxamide and their Chiral 9-Coordinate Ln3+ Complexes.

The R,R and S,S enantiomers of N,N'-bis(1-phenylpropyl)-2,6-pyridinedicarboxamide, L(Et), react with Ln3+ ions (Ln = La, Eu, Gd, and Tb) to give stable [Ln((R,R)- and (S,S)-L(Et))3]3+ in anhydrous acetonitrile solution, as evidenced by various spectroscopic measurements, including NMR and luminescence titrations. In addition to the characteristic Eu3+ and Tb3+ luminescence bands, the steady-state and time-resolved luminescence spectra of the aforementioned complexes show the residual ligand-centered emission of the 1ππ* to 3ππ* states, indicating an incomplete intersystem crossing (ISC) transfer from the 1ππ* to 3ππ* and ligand-to-Ln3+ energy transfer, respectively. The high circularly polarized luminescence (CPL) activity of [Eu(L(Et))3]3+ confirms that using a single enantiomer of L(Et) induces the preferential formation of one chiral [Eu(L(Et))3]3+ complex, consistent with the [EuL 3]3+ complexes formed with other ligands derived from a 2,6-pyridine dicarboxamide moiety. Furthermore, the CPL sign patterns of complexes with (R,R) or (S,S) enantiomer of L(Et) are consistent with the CPL sign pattern of related [LnL 3]3+ complexes with the (R,R) or (S,S) enantiomer of the respective ligands in this family.

Study on the Species Distributions of Dissolved U(VI) and Adsorbed U(VI) on Silica Surface

Dissolved hexavalent uranium can exist in the form of several different chemical species. Furthermore, species distributions depend on the pH value of the aqueous solution. Representatively, UO2 2+, UO2OH+, (UO2)2(OH)2 2+, and (UO2)3(OH)5 + species coexist in solutions at acidic and circumneutral pH values. When amorphous silica particles are suspended in an aqueous solution, the dissolved chemical species are easily adsorbed onto silica surfaces. In this study, it was examined whether the species distribution of the adsorbed U(VI) on a silica surface followed that of the dissolved U(VI) in an aqueous solution. Time-resolved luminescence spectra of three different dissolved species (UO2 2+, UO2OH+, and (UO2)3(OH)5 +) and two different adsorbed species (≡SiO2UO2, ≡SiO2(UO2)OH–, or ≡SiO2(UO2)3(OH)5–) were measured in the pH range 3.5−7.5. The spectral shapes of these chemical species were compared by changing the pH value; consequently, it was confirmed that the species distribution of the adsorbed U(VI) species was different from that of the dissolved U(VI) species.

Synthesis of multi-color luminescent ZnO nanoparticles by ultra-short pulsed laser ablation

Crystalline ZnO nanoparticles (NPs) are synthesized by ultra-short femtosecond (fs) pulsed laser ablation (PLA) of a zinc plate in deionized water, and are investigated by optical absorption and time resolved luminescence spectra in combination with the morphology and structure analysis. The comparison with previous experiments based on short nanosecond (ns) PLA highlights that pulse duration is a crucial parameter to determine the size and the optical properties of ZnO NPs. While short PLA generates NPs with average size S‾ of ~30 nm, ultrashort PLA allows to achieve much smaller NPs, S‾⩽10 nm, that evidence weak quantum confinement effects on both the absorption edge and the UV excitonic emission. Moreover, the defective nature of synthesized ZnO NPs gives rise to two visible photoluminescence bands: the first, centered around 2.3 eV and commonly associated with oxygen vacancies, unexpectedly blue-shifts on decreasing the NPs size; the second, peaked at 2.8 eV, shows a Lorentzian shape characteristic of a mobile exciton. Overall, these results demonstrate that PLA is a successful method to synthesize ZnO NPs with controlled luminescence properties, thus increasing their application in lighting technologies.

Observation of ultrahigh mobility excitons in a strain field by space- and time-resolved spectroscopy at subkelvin temperatures

We measured basic parameters such as the lifetime, mobility, and diffusion constant of trapped paraexcitons in cuprous oxide at very low temperatures (below 1 K) using a dilution refrigerator. To obtain these parameters, we observed the space- and time-resolved luminescence spectrum of paraexcitons in strain-induced trap potential. We extracted the lifetime of 410 ns from the measurements of the decay of the luminescence intensity. By comparing the experimental results and numerical calculations, we found that the mobility and the diffusion constant increase as the temperature of the paraexcitons decreases below 1 K. In particular, we obtained a mobility of 5.1e7 cm^2/V*s at the corresponding temperature of 280 mK. To the best of our knowledge, this value is the highest exciton mobility that has been measured. These results show that the mean free path of the paraexcitons reaches a size (~300 um) comparable to that of the cloud of trapped paraexcitons (~100 um). From our analyses, we found that the spatial distribution of the paraexcitons can reach a distribution that is defined by the statistical distribution function and the shape of the three-dimensional trap potential at ultra-low temperatures (well below 1 K). Our survey shows that the ultra-low temperature ensures that the Bose--Einstein condensation transition in a trap potential can be investigated by examining the spatial distribution of the density of 1s paraexcitons.

Electronic and Structural Dynamics of Dicyanoaurate Trimer in Excited State.

A trimer of dicyanoaurate has been studied as a model system of the covalent chemical bond formation. Here, we report the dynamics of dicyanoaurate trimer in water upon photoexcitation by femtosecond time-resolved luminescence (TL) and luminescence spectra at cyrogenic temperature. Temperature was varied as a means to control the medium flexibility as well as the population of isomers. A unique parallelism between the luminescence spectrum vs. time and vs. temperaturewas observed, which enables unambiguous luminescence band assignments and facilitates investigation of the dynamics. Upon photoexcitation to S1, intersystem crossing proceeds in an ultrafast manner within 20 fs due to the large spin-orbit coupling followed by a structural change from a loose bent to a tight linear form in 1.5 ps. Higher oligomerization occurs above the melting temperature. TL reveals a strong coherent excitation of the symmetric Au-Au stretching vibration at 74 cm-1 through the non-Condon effect.

O-Hydroxydibenzoylmethanate of boron difluoride: A complex with multi-stimuli-responsive emission effects.

The structural, luminescence and chemosensor properties of boron difluoride o-hydroxydibenzoylmethanate (1) have been investigated. In the concentrated solution, PE (polyethylene) matrix, and crystals of 1, one observes the formation of J-aggregates. The crystal structure of 1 is in compliance with that of J-aggregates of the "brickwork type" consisting of dimers that comprise excimer traps. In time-resolved luminescence spectra of 1 in PE films and crystals, one observes luminescence bands corresponding to the luminescence of excimer J-aggregates. At application of external stimuli on the crystals of 1 (heating, grinding), one observes changes in the luminescence spectrum caused by redistribution of intensities of excimer and J-aggregate bands. 1 could act as an optic chemosensor for probing amines vapors with different response rates and different sensitivities controlled by their morphologies.

Unraveling the Ultrafast Exciton Relaxation and Hidden Energy State in CH3NH3PbBr3 Nanoparticles

Recently organic–inorganic lead-halide perovskite nanoparticles (NPs) have been attractive as low-cost and high-conversion-efficient solar cells and light-emitting diode. The generation of the exciton and dissociation into free carriers are quite important for primary photoelectric conversion processes. In this study, we have examined the initial exciton dynamics of CH3NH3PbBr3 (MAPbBr3) NPs by femtosecond transient absorption spectroscopy and picosecond time-resolved luminescence spectroscopy. The ultrafast exciton quenching with a time constant of 200 fs was observed, which may be related with longitudinal optical phonon and/or lurching motion of MA cation in the excited state. In addition, higher electronic state with a short lifetime was clearly detected by the excitation intensity dependence of time-resolved luminescence and transient absorption spectra. These findings of MAPbBr3 NPs are very important not only for understanding the generation of charge carrier but also for constructing the high-effi...

Differentiation of black writing ink on paper using luminescence lifetime by time-resolved luminescence spectroscopy

The time-resolved luminescence spectra and the lifetimes of eighteen black writing inks were measured to differentiate pen ink on altered documents. The spectra and lifetimes depended on the samples. About half of the samples only exhibited short-lived luminescence components on the nanosecond time scale. On the other hand, the other samples exhibited short- and long-lived components on the microsecond time scale. The samples could be classified into fifteen groups based on the luminescence spectra and dynamics. Therefore, luminescence lifetime can be used for the differentiation of writing inks, and luminescence lifetime imaging can be applied for the examination of altered documents.

Influence of upper rim dibromo-substitution in bis-1,3-diketone calix[4]arenes on spectral properties of ligands and their lanthanide complexes

The present work introduces the synthesis and characterization of upper rim dibromo-substituted bis-1,3-diketone calix[4]arenes with hydroxy and propyloxy groups at the lower rim as ligands for Gd3+ and Tb3+ complexes. The dibromo-substitution does not affect 1:1 complex formation with the lanthanide ions arising from their coordination via two 1,3-diketonate groups incorporated at the upper rim of the calix[4]arene. The analysis of the time-resolved luminescence spectra of the Gd3+ complexes clearly demonstrates the notable enhancement of the decay time of the ligand triplet state, while the energy of the triplet state for the new dibromo-bis-1,3-diketones remains practically unchanged versus its non-substituted analogues. The latter tendency points to the heavy-atom effect on the energy transfer from the excited state to vibration levels of the dibromo-substituted ligand resulting in a decreased radiationless decay contribution. Measurements of Tb3+-centered luminescence indicate a better antenna effect (∼1.7) of dibromo-calix[4]arenes compared with its non-substituted counterpart.

Regulation on the aggregation-induced emission (AIE) of DNA-templated silver nanoclusters by BSA and its hydrolysates

The aggregation-induced emission (AIE) phenomenon of the metal nanoclusters (NCs) has been discovered quite recently, which is considered to be creative to improve the optical properties of NCs upon ligand aggregation. In the present study, we report an AIE system for double-stranded DNA-templated silver nanoclusters (AgNCs-dsDNA) by using bovine serum albumin (BSA) in solution, which induce a moderate emission enhancement of AgNCs (5-fold) and a blue-shift through a loosen interaction. In addition, significant luminescence enhancement (30-fold) is further stimulated by the addition of digestive enzyme to the system by altering the surface structure of the aggregated particles. The processes are observed directly through transmission electron microscopy (TEM), where the dispersed AgNCs spheres are aggregated in a large incompact sheet-like film by BSA; while further trypsin addition lead them into larger particles (>50nm) with higher density. And the intrinsic mechanism is explained well by UV–vis absorption and time-resolved luminescence spectra. The observed luminescence enhancement in step-II is attributed to the AIE through stronger interaction between the hydrolysates of BSA and the ligand dsDNA. Therefore, the optical properties of AgNCs-dsDNA are regulated well by the addition of BSA and trypsin in different amounts, which relates directly to the degree of aggregation and can be extended to other metal nanoclusters by employing the pairs of protein and related enzyme.

Self-Assembled Tb3+ Complex Probe for Quantitative Analysis of ATP during Its Enzymatic Hydrolysis via Time-Resolved Luminescence in Vitro and in Vivo.

To more accurately assess the pathways of biological systems, a probe is needed that may respond selectively to adenosine triphosphate (ATP) for both in vitro and in vivo detection modes. We have developed a luminescence probe that can provide real-time information on the extent of ATP, ADP, and AMP by virtue of the luminescence and luminescence lifetime observed from a supramolecular polymer based on a C3 symmetrical terpyridine complex with Tb3+ (S1-Tb). The probe shows remarkable selective luminescence enhancement in the presence of ATP compared to other phosphate-displaying nucleotides including adenosine diphosphate (ADP), adenosine monophosphate (AMP), guanosine triphosphate (GTP), thymidine triphosphate (TTP), H2PO4- (Pi), and pyrophosphate (PPi). In addition, the time-resolved luminescence lifetime and luminescence spectrum of S1-Tb could facilitate the quantitative measurement of the exact amount of ATP and similarly ADP and AMP within living cells. The time-resolved luminescence lifetime of S1-Tb could also be used to quantitatively monitor the amount of ATP, ADP, and AMP in vitro following the enzymatic hydrolysis of ATP. The long luminescence lifetime, which was observed into the millisecond range, makes this S1-Tb-based probe particularly attractive for monitoring biological ATP levels in vivo, because any short lifetime background fluorescence arising from the complex molecular environment may be easily eliminated.

Excited-State Dynamics of Oxyluciferin in Firefly Luciferase.

The color variations of light emitted by some natural and mutant luciferases are normally attributed to collective factors referred to as microenvironment effects; however, the exact nature of these interactions between the emitting molecule (oxyluciferin) and the active site remains elusive. Although model studies of noncomplexed oxyluciferin and its variants have greatly advanced the understanding of its photochemistry, extrapolation of the conclusions to the real system requires assumptions about the polarity and proticity of the active site. To decipher the intricate excited-state dynamics, global and target analysis is performed here for the first time on the steady-state and time-resolved spectra of firefly oxyluciferin complexed with luciferase from the Japanese firefly (Luciola cruciata). The experimental steady-state and time-resolved luminescence spectra of the oxyluciferin/luciferase complex in solution are compared with the broadband time-resolved firefly bioluminescence recorded in vivo. The results demonstrate that de-excitation of the luminophore results in a complex cascade of photoinduced proton transfer processes and can be interpreted by the pH dependence of the emitted light. It is confirmed that proton transfer is the central event in the spectrochemistry of this system for which any assignment of the pH-dependent emission to a single chemical species would be an oversimplification.

Detecting the origin of luminescence in Er3+-doped hexagonal Na1.5Gd1.5F6 phosphors.

Understanding site-selective fluorescence is one of valuable importance for spectrum modulation. In this Letter, we observed the existence of two non-equivalent Gd-activated crystallographic sites in an Er3+-doped hexagonal Na1.5Gd1.5F6 phosphor. It is proved that two green emissions from the S3/24 level separately originate from the Gd1 (540 nm) and Na2/Gd2 (550-555 nm) crystallographic sites, and the 657 nm red emission from the F9/24 level only originates from Na2/Gd2 site through using the time-resolved luminescence spectra. The 142.2% absolute enhancement of the red emission is realized through the synergistic effect of ultraviolet downconversion and infrared upconversion induced by the 370 nm and 1.54 μm dual-mode excitation.

Photoluminescence study of a broad yellow-emitting phosphor K2ZrSi2O7:Bi3+

The photoluminescence of a novel yellow emitting phosphor K2ZrSi2O7:Bi3+ that contains no rare earth ions was investigated. This phosphor was further evaluated as a color converter for white LEDs. The results indicate that K2ZrSi2O7:Bi3+ has strong absorption in 300–400nm region due to the 1S0→3P1 transition of Bi3+. Upon excitation into the 3P1 level of Bi3+, K2ZrSi2O7:Bi3+ gives bright and broad yellow emission (FWHM∼125nm) peaking at 560nm. Except for intensity, the spectral position and shape of the yellow emission band are the same for different concentrations of Bi3+ incorporated K2ZrSi2O7; Both the emission spectra measured at liquid nitrogen temperature (77K) and room temperature have no splitting and they can be well fitted by a single Gaussian profile; time resolved luminescence spectra reveal that the shape of the emission spectra remain unchanged with increasing delay time. These results indicate only one type of Bi3+ center exists in K2ZrSi2O7. Accompanied by a decrease of emission intensity, the emission of Bi3+ is blue-shifted upon heating (λmax=560nm at T=25°C vs. λmax=550nm at T=250°C), which is ascribed to the thermally active phonon-assisted tunneling from the excited states of lower-energy emission band to those of higher- energy emission band. The white light has been reached using K2ZrSi2O7:Bi3+ as a yellow emitting phosphor.