Time-resolved Luminescence Techniques Research Articles

Photoinduced Processes in Molecular and Supramolecular Arrays Based on Porphyrins and Acridinium Units

Multichromophoric arrays based on porphyrins are of high interest for their mimicry of naturally occurring photoinduced energy and electron transfer processes leading to energy collection and conversion. [1] Moreover, the rich photophysics and electrochemistry of porphyrins make them suitable components of molecular wires, switches or chemical sensors. [2] In this perspective, it is interesting to pursue the combination of porphyrins with units that can act as multiresponsive components by modifying their chemical and electronic structure upon chemical or redox stimuli. N-acridinium ions have been recently explored as a new class of switches that respond to various orthogonal stimulations (pH or electrochemical/photochemical inputs) that trigger their reversible conversion into the non-aromatic acridane form. [3] Few examples reporting the association of acridinium units and porphyrins indicate that these systems are characterized by fast photoinduced electron transfer reactions between the porphyrin donor and the acridinium acceptor. [4,5]We recently investigated the photophysical properties of molecular and supramolecular arrays based on porphyrins and acridinium units, where the type of porphyrin (free-base or metallated) and/or the form of the switchable component (acridinium or acridane) has been varied (Figure 1). We found that the association of porphyrins and acridinium ions always leads to ultrafast electron transfer processes, and that these reactions can be altered by changing the temperature or by converting the acridinium electron acceptor into an acridane energy donor. Moreover, the combination of two Zn-porphyrins with two acridinium/acridane units results in switchable molecular receptors able to coordinate suitable hosts. The photophysics of the arrays and of the complexes, analyzed by means of steady-state and time-resolved luminescence techniques and ultrafast transient absorption spectroscopy, will be herein presented and discussed.The work is supported by the H2020-MSCA-ITN-2017-765297 project “NOAH” and by the H2020-LC-SC3-2020-RES-RIA-101006839 project “CONDOR”.[1] M. Beyler, L. Flamigni, V. Heitz, J.-P. Sauvage, B. Ventura, Photochem. Photobiol. 2014, 90, 275-286.[2] Beletskaya I, Tyurin VS, Tsivadze AY, Guilard R, Stern C. Chem. Rev. 2009, 109, 1659-1713.[3] H.-P. J. de Rouville, J. Hu, V. Heitz, ChemPlusChem, 2021, 86, 110-129.[4] A. Edo-Osagie, D. Sánchez-Resa, D. Serillon, E. Bandini, C. Gourlaouen, H.-P. Jacquot de Rouville, B. Ventura, V. Heitz, C. R. Chim. 2021, 24, 1-9.[5] H. Kotani, K. Ohkubo, M. J. Crossley, S. Fukuzumi, J. Am. Chem. Soc., 2011, 133, 11092-11095.Figure 1. Structures of the studied arrays and schemes of the occurring photoinduced processes: a) bisacridinium-Zn(II) porphyrin conjugate, b) bisacridinium-diphenylporphyrin conjugate, c) bis(acridinium/acridane)-Zn(II) porphyrin receptors. Figure 1

Modulating Resonance Energy Transfer with Supramolecular Control in a Layered Hybrid Perovskite and Chromium Photosensitizer Assembly.

Recently, the low-dimensional organic-inorganic halide perovskites (OIHP) have been exploited heavily for their favorable exciton dynamics, broad-band emission, remarkable stability, and tunable band-edge excited-state energy compared to their 3D counterparts for potential optoelectronic applications. Low-dimensional perovskites are generally good candidates for utilization as room-temperature photoluminescence (PL) materials. Further, doping divalent transition metals like Mn2+ into OIHP is expected to introduce a 4T1-6A1-based low-energy luminescence emission around 600 nm; an optical property that is favorable for biomedical optoelectronics. Doping Mn2+ in the perovskite lattice is also expected to induce the generation of cytotoxic singlet oxygen species (1O2), a ROS that is being exploited for various therapeutic applications. To integrate these optical and therapeutic properties of a 2D (PEA)2PbBr4 (Pb PeV; PEA = phenylethylammonium cation) perovskite alloyed with Mn2+ ions (Mn:PbPeV) and the option for a photoinduced energy transfer process involving a Cr(III)-based 1O2 generating photosensitizer (CrPS), we designed a unique purpose-built nanoassembly (Mn:PbPeV@PCD) using the encapsulation properties of a water-soluble polymer derived from β-cyclodextrin (PCD). Here the PCD is observed to modulate the classical internal energy transfer of Pb2+ exciton to alloyed Mn2+ orange emission, resulting in the emergence of a new blue emission. The addition of CrPS into the Mn:PbPeV@PCD to generate the CrPS@Mn:PbPeV@PCD assembly results in restoring perovskite luminescence followed by the external energy transfer to CrPS. We have elucidated the mechanism of these cascade energy transfer processes between multiple components using steady-state and time-resolved luminescence techniques. Efficient ROS generation and its potential to induce an oxidation reaction of a biomolecule are realized using guanine as the target molecule. Further photoinduced cleavage studies with biomolecules confirmed the efficacy of the nanoassembly in inducing the cleavage of guanine-rich DNA. The study opens up a new direction in the field of perovskite for biomedical applications.

Synthesis and Photoluminescence Properties of MoS2/Graphene Heterostructure by Liquid-Phase Exfoliation.

Here, we report the synthesis of MoS2/graphene heterostructure in single-stage, liquid-phase exfoliation using a 7:3 isopropyl alcohol/water mixture. Further, the synthesized heterostructure was characterized using UV–visible and micro-Raman spectroscopies, transmission electron microscopy (TEM), and dynamic light scattering (DLS) analysis. UV–visible and micro-Raman analyses confirmed that the synthesized heterostructure had mostly few-layered (two-to-four sheets) MoS2. The photophysical properties of the heterostructure were analyzed using steady-state and time-resolved luminescence techniques. Enhanced photoluminescence was observed in the case of the heterostructure probably due to an increase in the defect sites or reduction in the rate of nonradiative decay upon formation of the sandwiched heterostructure. Applications of this heterostructure for fluorescence live-cell imaging were carried out, and the heterostructure demonstrated a better luminescence contrast compared to its individual counterpart MoS2 in phosphate-buffered saline (PBS).

Direct measurements of the reactivity of singlet oxygen to some persistent herbicides in aqueous solutions

Reactivity of the singlet oxygen (SO), which is assumed to be one of the important oxidizers in natural waters, towards to a set of persistent herbicides, was measured for the first time using time resolved luminescence technique. It was observed that rate constants of SO reactions with the majority of studied herbicides are less than 106 M−1s−1 allowing to conclude about negligible participation of SO in oxidation of the compounds in natural waters.

Time-resolved photoinduced charge dynamics of Cd chalcogenide-based materials

We have performed a comparative analysis of the photocharging dynamics of quantum dots (CdSe–CdS core–shell nanoparticles in toluene) and a bulk CdS single crystal by using time-resolved luminescence and transient grating techniques. The quantum dots were obtained through a colloidal synthesis method in aqueous–organic media with the average sizes of 2 nm and 2.9 nm. It has been shown that the relaxation of the photocharging dynamics in quantum dots is well fitted by the double-exponential decay function with time constants of a few and tens of picoseconds, which indicates that the energy loss of photoinduced charges is mainly the result of electron–phonon interaction.

Two-photon absorption and upconversion luminescence of colloidal CsPbX3 quantum dots

The nonlinear optical and the upconversion luminescence (UCL) properties of CsPbX3 (X = Br or its binary mixtures with Cl, I) quantum dots (QDs) are investigated by femtosecond open-aperture (OA) Z-scan and time-resolved luminescence techniques in nonresonant spectral region. The OA Z-scan results show that CsPbX3 QDs have strong reverse saturable absorption (RSA), which is ascribed to two-photon absorption. Partially changing halide composition from Cl to Br, to I, two-photon absorption cross sections become larger at the same laser excitation intensity. The composition-tunable nonlinear absorption should be attributed to the gradual decrease of the lowest direct band gaps with the halide substitute. Moreover, the strong UCL can be observed under near infrared femtosecond laser excitation. Halide composition-tunable UCL dynamics of CsPbX3 QDs is analyzed by use of two-exponential fitting with deconvolution. When CsPbX3 QDs have similar sizes (10–13 nm), with partially changing halide composition from Cl to Br, to I, the average UCL lifetime becomes longer due to the variation of Kane energy. Our findings suggest all-inorganic perovskite QDs can be used as excellent gain medium for high-performance frequency-upconversion lasers and provide reference to engineer such QDs toward practical optoelectronic applications.

Laser-induced time resolved luminescence of natural sylvite KCl

Natural sylvite samples have been studied by laser-induced time-resolved luminescence techniques. The specific combinations of luminescence and excitation spectra together with luminescence decay times enabled their interpretation as Pb2+ and O2- emission centers. Such conclusions have been supported by luminescence study of artificial KCl crystals, activated by the corresponding emission centers.

Bright emission via energy transfer from Dy to Tb in Bi2SiO5 nanophosphor

The present article discusses the optical and structural properties of Tb and Dy co-doped Bi2SiO5 nanophosphors which were synthesized by Co-precipitation method. The synthesized sample contains plate-like morphology of uniform thickness ∼200 nm. Prepared samples were found of average crystallite size ∼20 nm, which yield bright yellow dominating white emission and green emission, in Dy: Bi2SiO5 and Tb: Bi2SiO5 nanophosphor, respectively under UV-light excitation. We have reported one-way efficient energy transfer from Dy to Tb ion, which facilitates precise colour tuning ability. The energy transfer phenomenon was well explored using, photoexcitation, photoluminescence and time-resolved luminescence techniques.

Observation of two-way multichannel interaction among Dy and Eu ions in Bi2SiO5 nanophosphor

A series of Dy3+ and Eu3+ ion doped Bi2SiO5 nanophosphors were synthesized by hydrothermal method. A comprehensive structural and optical characterization were performed using various techniques including powder X-ray diffraction, UV-Infrared absorption, photoluminescence, time-resolved luminescence technique etc. Crystalline size of the synthesized nanophosphors was found to be ∼25 nm, depending on the doping concentration of the active ions. Under the blue light excitations (386 nm and 393 nm) the Dy3+:Bi2SiO5 and Eu3+:Bi2SiO5 nanophosphors yield characteristic yellowish white light and yellow/red emissions, respectively. In binary co-doped, Dy:Eu:Bi2SiO5, excitation of individual ion results from another doped ion, in addition to the emission from resonantly excited ion. Observation of emission from acceptor ions, confirm the effective mutual interaction between the doped ions and existence of two-way energy transfer process. Various energy transfer parameters including the rate of energy transfer efficiency were estimated. A predominate multipole interaction was concluded for the energy transfer through multichannel interaction which yield white light on 350 nm and 386 nm excitations. CIE coordinates were estimated for various excitations which fall well within the gamut of white light.

Efficiency of singlet oxygen generation by fulvic acids and its influence on UV photodegradation of herbicide Amitrole in aqueous solutions

pH-dependent efficiency of singlet oxygen (1O2) generation by fulvic acids (FAs) from different sources was estimated by time-resolved luminescence technique. All FAs turn up the highest quantum yields of 1O2 for neutral and alkali solutions [ϕ532(1O2)] = (0.3•2.5)í10•2] and 3•5-fold decrease in ϕ532(1O2) for acidic solutions. Potential of FA ChangSheng (the best 1O2 generating agent among investigated FAs) in relation to photodegradation of non-UVA-absorbing herbicide Amitrole (3-amino-1,2,4-triazole) was demonstrated.

Vibrational and spectroscopic analysis of white light emitting Bi2SiO5 nanophosphor

A series of Dy3+ ion activated Bi2SiO5 nanophosphors were synthesized by the hydrothermal and coprecipitation methods. Various structural and optical characterizations were made using X-ray diffraction, Scanning and Transmission electron microscopy, UV–Visible-Infrared absorption, Raman Spectroscopy, Photoluminescence, Time resolved luminescence techniques etc. Dy3+ ion doped samples yields characteristic bright yellow and blue emissions, on resonant excitation with 349nm and 386nm. The intensity ratio of the yellow/blue peaks was found to be function of Dy ion concentration and synthesis method. We have achieved white colour emission at 1.5mol% Dy concentration, CIE coordinate (0.36, 0.4) of which fall well within gamut of white light. The time-resolved fluorescence reveals decrease in radiative lifetime values with increasing Dy3+ ions concentration. A comparison between the samples synthesized by different methods, and Dy ion concentrations has been made and detail photo-physics involved is presented in the article.

Comparing the luminescence processes of YVO4:Eu and core-shell YVO4@YF3 nanocrystals with bulk-YVO4:Eu

Comparative analysis of bulk, non-coated and core-shelled nanocrystalline YVO4:Eu was performed by means of time-resolved luminescence and VUV excitation luminescence spectroscopy techniques. Nanocrystalline YVO4:Eu samples – both as-prepared and YF3 core-shelled – have been synthesized by means of a microwave-assisted synthesis in ionic liquids, which allows to obtain 10–12nm nanoparticles with high crystallinity. The results show noticeable differences between bulk and nanocrystalline YVO4:Eu in photoluminescence experimental data, which explains by influence of the nanocrystal surface. A YF3 core-shell layer around YVO4:Eu nanoparticles partially recovers the intensity of the Eu3+ emission. It is demonstrated that the Eu3+ luminescence recovery is achieved at the expense of the suppression of the intrinsic emission but not due to the passivation of surface loss centers in core-shelled nanocrystals. It is also shown that surface loss processes are the reason of the degradation of energy transfer efficiency from the host lattice to Eu3+ under high-energy excitations in vacuum ultraviolet spectral range.

Structural and photophysical investigations of bright yellow emitting Dy: ZnAl2O4 nanophosphor

ZnAl2O4:Dy nanophosphors were synthesized using co-precipitation and hydrothermal methods. Various structural and optical characterizations were made using X-ray diffraction (XRD), Transmission electron microscopy, Scanning electron microscopy, UV-Visible absorption, Infrared absorption, photoluminescence and time resolved luminescence techniques. Dy3+ doped samples showed yellow dominating multicolour emission on excitation with 348nm. We have estimated J–O parameters and other various radiative parameters like quantum efficiency, Stimulated emission cross-section etc. Considerable effect of SiO2 was noticed on crystalline size and emission intensity of Dy ions. A comparison between the samples synthesized by different methods, and Dy concentration has been made and detail report presented in the article.

A series of iridophosphors with tunable excited states for hypoxia monitoring via time-resolved luminescence microscopy

A series of iridophosphors with different oxygen sensitivity has been designed and synthesized for hypoxia imaging by time-resolved luminescence techniques.

A phosphorescent Ir(iii) complex with formamide for the luminescence determination of low-level water content in organic solvents

A novel formamide-containing Ir(iii) complex was designed and synthesized for the determination of water content with low LOD and LOQ by a time-resolved luminescence technique.

White emitting phosphors based on glasses of the type 10AlF3–10TiO2–39PbO–30H3BO3–10SiO2–xEu2O3–(1−x)Tb2O3: An energy transfer study

Glasses consisting of heavy metal oxides, a metal fluoride and two lanthanoid oxides (as dopants) of the type 10AlF3–10TiO2–39PbO–30H3BO3–10SiO2–xEu2O3–(1−x)Tb2O3 were prepared as phosphors with different molar ratio x. The un-doped matrix glass was characterized by XRD and DSC techniques. Its structure was also studied by FTIR techniques that suggested the presence of B–O−, B–Ø–B, Pb–O, Al–Ø–B and Al–O− bonds as well as [BO3]3−, [BØO3], [BØ4], and [SiØ4] structural units as well as Ln–O–Ln clusters. For the Eu3+ and Tb3+ co-doped luminescent glasses optical absorption, luminescence and excitation spectra were recorded as well as time resolved luminescence techniques was used. Two luminescence effects were analyzed, viz. cross-relaxation Tb3+→Tb3+ energy transfer and Tb3+→Eu3+ energy transfer. The CIE diagram suggests that especially the glass co-doped with Eu3+ and Tb3+ in molar ratio x=0.5 can be recognized as a cold white phosphor.

Luminescent GeO2–Pb–Bi2O3 glasses co-doped with Tb3+1 and Eu3+: Excitation energy transfer and color chromaticity

Heavy metal oxide glass of the type GeO2–PbO–Bi2O3 was applied as a matrix for luminescent materials co-doped with Tb3+ and Eu3+ ions of different molar ratio. The undoped glass matrix with the composition 80GeO2–19PbO–1Bi2O3 was characterized by XRD and DSC techniques. Its structure was studied by FTIR spectroscopy. The FTIR spectra suggested that GeO4, GeO6, BiO3, BiO6, PbO3 and PbO4 structural units are present in the glass. In the case of the 79GeO2–19PbO–Bi2O3–xEu2O3–(1−x)Tb2O3 luminescent glasses, reflection, luminescence and excitation spectra were recorded as well as time resolved luminescence technique was used. Two luminescence effects were analyzed, viz. cross relaxation and Tb3+→Eu3+ energy transfer.

Laser-induced time-resolved luminescence of natural margarosanite Pb(Ca, Mn)2Si3O9, swedenborgite NaBe4SbO7 and walstromite BaCa2Si3O9

Visual luminescence of natural margarosanite, swedenborgite and walstromite is well known for mineralogists, but their spectral characteristics and interpretation were still missing. We studied those minerals by laser-induced time-resolved luminescence technique, described the corresponding spectral and kinetic parameters and interpreted the luminescence centers as follows: margarosanite – Mn 2+ , Mn 2+ clusters, Pb 2+ and Ce 3+ ; swedenborgite – Sb 3+ ; walstromite – Mn 2+ , Eu 2+ and trivalent rare-earth elements.

A homogeneous single-label quenching resonance energy transfer assay for a δ-opioid receptor–ligand using intact cells

This study, a homogeneous assay system for delta opioid receptor binding ligands has been developed using Quenching Resonance Energy Transfer (QRET). The QRET system allows receptor-ligand binding assays on intact cells using a single-label approach and a nonspecific quenching mechanism. Binding of antagonists or agonists to the receptor can be defined using a europium(III) labeled ligand. In the presence of the unlabeled ligand the labeled ligand is displaced and remains in solution. The non-bound labeled ligand is not protected by the target receptor, and the luminescence signal is quenched. For this objective, a Eu(III) labeled peptide molecule with three different linkers (AX0, AX1 and AX2) was designed. Peptides were evaluated using the homogeneous QRET technique, radioligand binding assays and the heterogeneous time-resolved luminescence (TRL) technique. Using the Eu-AX0 peptide and the QRET method, a panel of opioid compounds (naltrexone, naltrindole, SCN-80, DPDPE and DAMGO) was tested to prove the assay performance. The signal-to-background ratio for the tested opioid ligand ranged from 3.3 to 12.0. The QRET method showed prominent performance also in high DMSO concentrations. QRET is a homogenous and a non-radioactive detection system for screening and this is the first attempt to utilize peptide ligands in the QRET concept.

Laser-induced time resolved luminescence of natural grossular Ca3Al2(SiO4)3

Natural grossular samples from Franklin, NJ Sierra de Cruces Range, Coahuila, Mexico, Asbestos, Canada and Africa (Mali) have been studied by laser-induced time-resolved luminescence techniques. The specific combinations of luminescence and excitation spectra together with luminescence decay times enabled their interpretation as Mn2+, Mn3+, Mn4+, V2+, Ni2+ and REE3+ emission centers. Such conclusions have been partly supported by luminescence study of artificial garnets activated by the corresponding potential emission centers.