Luminescence Lifetime Measurements Research Articles

Luminescence and two-photon absorption assisted optical limiting properties of Ag-doped CdWO4 nanorods

The emerging demand for the fabrication of nonlinear optical materials with high limits of optical power is obvious in nonlinear optics due to their wide application in photonic devices. We report the linear and third-order nonlinear optical properties of Ag-doped CdWO4 nanorods and their dependence on Ag-doping concentration. CdWO4 nanorods with different Ag concentrations were synthesized by the chemical precipitation method and characterized by UV–Vis absorption, X-ray diffraction (XRD), Raman, Photoluminescence and its lifetime studies, X-ray Photoelectron spectroscopy and Transmission Electron Microscopy (TEM). The introduction of Ag ions has led to an increased redshift in the CdWO4 absorption spectra extended into longer wavelength bands, thus enhancing optical absorption within the visible range. The XRD pattern showed that the nanorods crystallized in a monoclinic wolframite structure. The incorporation of Ag in CdWO4 decreases the luminescence emission intensity due to surface quenching effect. Luminescence lifetime measurement reveals the longer decay lifetime for Ag-doped CdWO4 nanorods due to the reduction of density of defects and deep trap state. The nonlinear optical behaviour of the nanorods was investigated by an Open aperture Z-scan technique at 532 nm using pulsed wave Nd: YAG laser. Experimental results showed that reverse saturable absorption is responsible for the observed nonlinearity in the nanorods. The addition of Ag can significantly improve the nonlinear absorption coefficient and optical limiting effects of CdWO4 which can be used as a potential material in nonlinear optical devices.

Orange luminescence of α-Al2O3 related to clusters consisting of F centers and divalent cations.

The orange luminescence of α-Al2O3 under UV excitation is characterized by a 2.07-eV orange broadband emission that has not yet been elucidated. This emission is present in natural and synthetic crystals and powders, as well as in Be-treated samples. All orange-luminescent materials have low Fe concentration (mostly <1000 ppm) with traces of divalent cations, mostly Mg, or Be in Be-diffused material (dozens of ppm). Mg2+, Mn2+, and Be2+ cations substitute for trivalent Al. To accommodate the charge deficit, several defects are created, including oxygen vacancies also called F centers. Indeed, our excitation spectra revealed the presence of several different F centers (F, F+, and clustered F2, F2 +, F2 2+) in those samples. However, the thermal stability and the measured luminescence lifetimes do not match with previously reported characteristics of isolated F centers. Based on our experiments, we suggest that a complex aggregate of two F centers (F2 2+) trapped at divalent cations is a major cause of this uncommon microsecond lifetime emission, even if a variety of other defects, including Cr3+, V3+, or interstitial Al3+, are present.

Photosensitizers Based on Bichromophoric Dyads Combining Ru(II)-Polypyridyl Complexes and Dissymmetric Perylene Monoimide Derivatives: The Nontrivial Role of Ligand Substitution.

The covalent modification of Ru(II) polypyridyl complexes (RPCs) with organic chromophores is a powerful strategy to obtain metal-based photosensitizer agents (PSs) with improved performance for application in photodynamic therapy (PDT). In this respect, perylene-imides are of particular interest due to their rich chemical-physical repertoire, and it is therefore quite surprising that their combination with RPCs has been poorly considered so far. Herein, we report on the photophysical behavior of two newly synthesized RPCs bearing a perylene monoimide appendant (PMI-Ad). Differently from the majority of RPCs-perylene-imides dyads, these chromophores are dissymmetric and are tethered to the metal centers through a single C-C bond in the 3- or 5-position of 1,10-phenanthroline (Ru-3PMI-Ad and Ru-5PMI-Ad). Both compounds show excellent singlet oxygen photosensitizing activity, with quantum yields reaching >90% in the case of Ru-3PMI-Ad. A combined spectroscopic and theoretical analysis, also involving transient absorption and luminescence lifetime measurements, demonstrates that both compounds undergo intersystem crossing on a very fast time scale (tens of picoseconds) and with high efficiency. Our results further demonstrate that the increased electron delocalization between the metal center and the PMI-Ad chromophore observed for Ru-3PMI-Ad additionally contributes to increase the singlet oxygen quantum yields by prolonging the lifetime of the triplet state.

Comparing Sensor Fusion and Multimodal Chemometric Models for Monitoring U(VI) in Complex Environments Representative of Irradiated Nuclear Fuel.

Optical sensors and chemometric models were leveraged for the quantification of uranium(VI) (0-100 μg mL-1), europium (0-150 μg mL-1), samarium (0-250 μg mL-1), praseodymium (0-350 μg mL-1), neodymium (0-1000 μg mL-1), and HNO3 (2-4 M) with varying corrosion product (iron, nickel, and chromium) levels using laser fluorescence, Raman scattering, and ultraviolet-visible-near-infrared absorption spectra. In this paper, an efficient approach to developing and evaluating tens of thousands of partial least-squares regression (PLSR) models, built from fused optical spectra or multimodal acquisitions, is discussed. Each PLSR model was optimized with unique preprocessing combinations, and features were selected using genetic algorithm filters. The 7-factor D-optimal design training set contained just 55 samples to minimize the number of samples. The performance of PLSR models was evaluated by using an automated latent variable selection script. PLS1 regression models tailored to each species outperformed a global PLS2 model. PLS1 models built using fused spectra data and a multimodal (i.e., analyzed separately) approach yielded similar information, resulting in percent root-mean-square error of prediction values of 0.9-5.7% for the seven factors. The optical techniques and data processing strategies established in this study allow for the direct analysis of numerous species without measuring luminescence lifetimes or relying on a standard addition approach, making it optimal for near-real-time, in situ measurements. Nuclear reactor modeling helped bound training set conditions and identified elemental ratios of lanthanide fission products to characterize the burnup of irradiated nuclear fuel. Leveraging fluorescence, spectrophotometry, experimental design, and chemometrics can enable the remote quantification and characterization of complex systems with numerous species, monitor system performance, help identify the source of materials, and enable rapid high-throughput experiments in a variety of industrial processes and fundamental studies.

Lanthanide MOF-based luminescent sensor arrays for the detection of castration-resistant prostate cancer curing drugs and biomarkers.

In recent years, castration-resistant prostate cancer (CRPC) has profoundly impacted the lives of many men, and early diagnosis of medication and illness is crucial. Therefore, a highly efficient detection method for CRPC biomarkers and curing drugs is required. However, the complex and diverse structures of CRPC drugs pose significant challenges for their detection and differentiation. Lanthanide metal-organic frameworks (Ln-MOFs) show great potential for sensing applications due to their intense and characteristic luminescence. In this work, a series of new bimetallic Ln-MOFs (EuxTb1-x-MOF) based luminescent sensor arrays have been developed to identify CRPC drugs, including in mixtures, via principal component analysis (PCA) and hierarchical cluster analysis (HCA) methods. These Ln-MOFs are built with a highly conjugated H2L linker (H2L = 5-(4-(triazole-1-yl)phenyl)isophthalic acid) and exhibit robust strong luminescence emissions (mainly located at 543 and 614 nm) and high energy transfer efficiencies. More specifically, Eu0.096Tb0.904-MOF (MOF 3) has demonstrated good sensing performances for CRPC curing drugs in real human serum samples. Furthermore, the curing drug hydroxyflutamide has been combined with MOF 3, to construct a robust composite sensing platform MOF 3@hydroxyflutamide for highly efficient detection of CRPC biomarkers such as the androgen receptor (AR) and prostate-specific antigen (PSA). Finally, luminescence lifetime measurements, zeta potential measurements, and density functional theory (DFT) calculations were performed to gain insights into the sensing mechanism.

Highly luminescent Gd2O2S:Er3+,Yb3+ upconversion microcrystals obtained by a time- and energy-saving microwave-assisted solid-state synthesis

Er3+-doped and Er3+,Yb3+-co-doped Gd2O2S are one of the most efficient upconversion (UC) materials available to date. However, preparing lanthanide oxysulfides can be challenging as it requires several hours of heating at>1000 °C in high power furnaces. Nonetheless, in designing a new synthesis technology for UC materials, one should consider that these systems suffer from defect quenching, responsible for significant optical energy losses. In this work, the microwave-assisted solid-state (MASS) synthesis was explored as an alternative to synthesize this class of materials, using two different starting compounds – lanthanide oxides (Ln2O3) and hydroxycarbonates (Ln(OH)CO3), where Ln3+: Gd, Er, Yb. Different Er3+,Yb3+ concentrations were investigated, and the Er3+(5%),Yb3+(5%) and Er3+(1%),Yb3+(10%) were shown to give the most intense UC output comparable to commercially available materials. Using Ln(OH)CO3 instead of the more common Ln2O3 for the MASS synthesis contributed to higher UC efficiencies and a more homogeneous Er3+ and especially Yb3+ distribution through the Gd2O2S lattice as verified by luminescence lifetime measurements. These high-quality materials were prepared in a simple two-step synthesis of 50 min and using a domestic microwave oven, leading to a remarkable decrease of 79% in processing time and 93% in energy consumption, making the MASS method suitable to be explored as an alternative synthesis methodology for high performance UC materials.

Bipyridil-based chelators for Gd(III) complexation: kinetic, structural and relaxation properties.

In the last 20 years, research in the field of MRI (magnetic resonance imaging) contrast agents (CAs) has been intensified due to the emergence of a disease called nephrogenic systemic fibrosis (NSF). NSF has been linked to the in vivo dissociation of certain Gd(III)-based compounds applied in MRI as CAs. To prevent the dechelation of the probes after intravenous injection, the improvement of their in vivo stability is highly desired. The inertness of the Gd(III) chelates can be increased through the rigidification of the ligand structure. One of the potential ligands is (2,2',2'',2'''-(([2,2'-bipyridine]-6,6'-diylbis(methylene))bis(azanetriyl))tetraacetic acid) (H4DIPTA), which has been successfully used as a fluorescent probe for lanthanides; however, it has never been considered as a potential chelator for Gd(III) ions. In this paper, we report the thermodynamic, kinetic and structural features of the complex formed between Gd(III) and DIPTA. Since the solubility of the [Gd(DIPTA)]- chelate is very low under acidic conditions, hampering its thermodynamic characterization, we can only assume that its stability is close to that determined for the structural analogue [Gd(FENTA)]- (H4FENTA: (1,10-phenanthroline-2,9-diyl)bis(methyliminodiacetic acid)), which is similar to that determined for the agent [Gd(DTPA)]2- routinely used in clinical practice. Unfortunately, the inertness of [Gd(DIPTA)]- is significantly lower (t1/2 = 1.34 h) than that observed for [Gd(EGTA)]- and [Gd(DTPA)]2- as a result of its spontaneous dissociation pathway during dechelation. The relaxivity values of [Gd(DIPTA)]- are comparable with those of [Gd(FENTA)]- and somewhat higher than the values characterizing [Gd(DTPA)]2-. Luminescence lifetime measurements indicate the presence of one water molecule (q = 1) in the inner sphere of the complex with a relatively high water exchange rate (k298ex = 43(5) × 106 s-1). DFT calculations suggest a rigid distorted tricapped trigonal prismatic polyhedron for the Gd(III) complex. On the basis of these results, we can conclude that the bipyridine backbone is not favourable with respect to the inertness of the chelate.

Bright green emitting Terbium-MOF with high quantum yield achieved through post synthetic modifications

A luminescent material with high brightness and good quantum yield is the need of our multifunctional applications in the area of light emitting diodes (LEDs), bioimaging and anticounterfeiting. But most of the work in this area focuses on lanthanide ion doped inorganic materials which have issues with lattice strain, doping related issues of/and charge compensating defect, and lack of tunability. Here in this work we have utilized the potential of metal organic framework (MOF) for inducing terbium luminescence in Tb-BDC-NH2 (BDC = 1, 4-benzenedicarboxylate) MOF and probe the effect of different organic linker's viz. 2-pyridine carboxaldehyde (PC), maleic anhydride (MA), sulfamic acid (SA), diphenylphosphoryl chloride (DPC), etc. All the samples revealed green luminescence of terbium via ligand sensitization through BDC. The highest emission intensity with many fold increases in green emission with absolute quantum yield (QY) ∼ 33% was observed in Tb-BDC-DPC. The same has been ascribed to highest host sensitized energy transfer and unique rod shaped morphology of Tb-BDC-DPC. Luminescence lifetime measurements suggested non-homogenous distribution of terbium ions in the MOF with majority having non-asymmetric environment. High QY, longer excited state lifetime coupled with rod shaped morphology and higher thermal stability makes Tb-BDC-DPC an excellent candidate for green phosphor for phosphor converted light emitting diodes (pc-LEDs).

Luminescence properties of europium (III)-based metal–organic frameworks: Influence of varied organic linkers

Four new functionalized europium (Eu) based MOFs; Eu-BDC-PC, Eu-BDC-MA, Eu-BDC-SA, and Eu-BDC-DPC were synthesized with different organic linker's through post synthetic modification (PSM) strategy using Eu-BDC-NH2. The obtained Eu-MOFs were investigated for photoluminescence studies. Pristine Eu-BDC-NH2, functionalized Eu-BDC-PC and Eu-BDC-DPC depicted very intense red emission. While, Eu-BDC-MA and Eu-BDC-SA depicted fairly low red emission, this is attributed to differences in energy transfer from linkers to europium metal. The asymmetry ratio values of pristine Eu-BDC-NH2 and functionalized Eu-BDC-PC suggested that very low symmetry around europium ion. On the other hand, asymmetry value is relatively lower in Eu-BDC-DPC indicates the high symmetry around europium metal compared to Eu-BDC-NH2 and Eu-BDC-PC. Luminescence lifetime measurements in all the samples depicted monoexponential decay suggested homogenous distribution of europium ions in the MOF without inversion symmetry. The fluorescence lifetime values of all the functionalized Eu-MOFs (<0.57 ms) are less than the pristine Eu-BDC-NH2 (0.87 ms). The color correlated temperature (CCT) value of Eu-BDC-MA (10,000 K) and Eu-BDC-SA (4800 K) suggested near white emission with bluish hue know as cool white. Judd-Ofelt analysis also performed for all the Eu-MOFs. The trend in JO parameter and branching ratio suggests high color purity of pristine and Eu-BDC-PC samples where the Eu-BDC-DPC samples has higher excited state lifetime. Therefore, the work explained here will surely give a path to synthesize varied Ln-based MOFs with high efficiency for optoelectronic devices and LEDs by further tuning the light via PSM.

Simultaneous Occurrence of Vapochromism and Vapoluminescence in Formaldehyde-Responsive Amino-Functionalized Copper(I) Polymorphic Coordination Polymers

The use of vapor-responsive chromic materials in sensing applications for the detection of harmful volatile organic chemicals is rapidly expanding. Herein, four new amino-functionalized Cu(I) coordination polymers of [CuI(pyt-NH2)]n (1) and (2) and [CuSCN(pyt-NH2)]n (3) and (4) (where pyt-NH2 = 2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole) were successfully synthesized. Single-crystal X-ray diffraction analysis reveals that 1 and 2 are iodo-based polymorphs, while 3 and 4 are thiocyanato-based polymorphs. They possess densely diverse crystalline architectures decorated by uncoordinated amino groups as a binding site. Also, 1-4 show a variety of color and luminescence based on the structural diversity. Remarkably, 1 and 2 undergo the change of color and naked-eye solid-state luminescence in response to formaldehyde (FA) vapor, demonstrating simultaneous vapochromism and vapoluminescence. The chromic Cu(I) coordination polymers in this work present for the first time dual-mode vapochromism and vapoluminescence in a highly selective response to FA vapor. The responsive mechanism has been clarified by Fourier transform infrared spectroscopy (FT-IR), electrospray ionization mass spectrometry (ESI-MS), 1H nuclear magnetic resonance (NMR), powder X-ray diffraction (PXRD), and luminescence lifetime measurements, which reveal carbinolamine formation via the specific reaction between FA and the active amino groups of coordinated pyt-NH2. The carbinolamine formation can trigger the structural transformation of 1 and 2, leading to the concurrently selective vapochromism and vapoluminescence induced by FA vapor.

Microsecond-resolved smartphone time-gated luminescence spectroscopy.

Time-gated luminescence spectra are usually measured by laboratory instruments equipped with high-speed excitation sources and spectrometers, which are always bulky and expensive. To reduce the reliance on expensive laboratory instruments, we demonstrate the first, to the best of our knowledge, use of a smartphone for the detection of time-gated luminescence spectra. A mechanical chopper is used as the detection shutter and an optical switch is placed at the edge of the wheel to convert the chopping signal into a transistor-transistor logic (TTL) signal which is used to control the excitation source and achieve synchronization. The time-gated luminescence spectra at different delay times of Eu(TTA)3 powder and the solutions of Eu-tetracycline complex are successfully detected with a temporal resolution of tens of microseconds by the proposed approach. We believe our approach offers a route toward portable instruments for the measurement of luminescence spectra and lifetimes.

Experimental and Theoretical Studies of the Site Occupancy and Luminescence of Ce3+ in LiSr4(BO3)3 for Potential X-ray Detecting Applications.

Ce3+-doped LiSr4(BO3)3 phosphors have been prepared by a high-temperature solid-state reaction method, and structural refinement of the host compound has been performed. The excitation and emission spectra in the vacuum ultraviolet-ultraviolet-visible range at cryogenic temperatures reveal that Ce3+ ions preferentially occupy eight-coordinated Sr2+ sites in LiSr4(BO3)3. Such experimental attribution is well corroborated by the calculated 4f-5d transition energies and defect formation energies of Ce3+ ions at two distinct Sr2+ sites in the first-principles framework. In addition, the doping concentration-dependent luminescence and the temperature-dependent luminescence are systematically investigated by luminescence intensity and lifetime measurements, respectively. This shows that concentration quenching does not occur in the investigated doping range, but inhomogeneous broadening exists in the concentrated samples. With the estimated thermal quenching activation energy, the discussions on the thermal quenching mechanisms suggest that the thermal-ionization process of the 5d electron is a dominant channel for thermal quenching of Ce3+ luminescence, despite the fact that thermally activated concentration quenching cannot be excluded for the highly doped samples. Finally, the X-ray excited luminescence measurement demonstrates the promising applications of the phosphors in X-ray detection.

Simultaneous quantification of uranium(VI), samarium, nitric acid, and temperature with combined ensemble learning, laser fluorescence, and Raman scattering for real-time monitoring.

Laser-induced fluorescence spectroscopy (LIFS), Raman spectroscopy, and a stacked regression ensemble was developed for near real-time quantification of uranium(VI) (1-100 μg mL-1), samarium (0-200 μg mL-1) and nitric acid (0.1-4 M) with varying temperature (20 °C-45 °C). LIFS applications range from fundamental lab-scale studies to real-time process monitoring at industrial levels, such as nuclear reprocessing applications, provided the phenomena affecting the fluorescence spectrum are accounted for (e.g., absorption, quenching, complexation). Multiple chemometric models were examined and compared to a more traditional multivariate regression approach called partial least squares (PLS). Results obtained on synthetic samples selected using D-optimal experimental design indicated that a stacked regression method, which included ridge regression, random forest, PLS, and an eXtreme gradient boost algorithm, successfully measured uranium(VI) concentrations directly in nitric acid without measuring luminescence lifetimes or standard addition. The top model resulted in percent root-mean-square error of prediction values of 5.2, 1.9, 3.0, and 2.3% for U(VI), Sm3+, HNO3, and temperature, respectively. The approach may be useful for quantifying fluorescent fission products (e.g., Sm3+) to provide information on burnup of irradiated nuclear fuel. This novel framework reinforces the applicability of LIFS for real-time applications in nuclear fuel cycle applications.

Confinement of Highly Luminescent Silver Nanoclusters in FAUY Zeolite: A Study on the Formation Effects of Silver Nanoclusters and the Sensitization of Tb3+

In this research, highly luminescent silver nanoclusters (Ag NCs) were prepared by using Na-FAUY zeolite as a scaffold to hinder their aggregation, and efficient energy transfer from Ag NCs to Tb3+ was realized in Ag+-Tb3+ dual-exchanged Na-FAUY zeolites and then proved by steady spectral and luminescence lifetime measurements. Furthermore, the effects of Ag+ loading amount, thermal treatment, and Tb3+ loading on the luminescence properties of Ag NCs were studied, and the optimized doping and preparing conditions were obtained. X-ray photoelectron spectroscopy together with spectral measurements indicated that the available sites for Tb3+ and Ag+ are competitive and Tb3+ doping may hinder the effective formation of Ag NCs. It is also indicated that the loading of Tb3+ may lead to reduced Si/Al ratios, which greatly influence the luminescence property and chemical state of Ag NCs, e.g., a high Si/Al ratio leads to blueshift emission and stronger ionic of Ag NCs. This research may benefit the design of Ag NCs-involved luminescent zeolites that have potential applications for photonic devices like LEDs and 3D displays.

Spectroscopic properties and energy transfer in Nd3+/Yb3+ co-doped yttrium aluminum garnet

High-quality Nd,Yb:YAG crystal with 5 at. % Yb3+ and 0.5 at. % Nd3+ was grown using the Czochralski method. A complete optical characterization was reported including absorption, excitation spectra and luminescence lifetime measurements at room temperature and emission spectra at temperatures ranging from 300 K to 800 K. The emission spectra of Nd3+/Yb3+ co-doped YAG were measured for different excitation wavelengths 808 nm and 940 nm. The presence of Yb3+ emission after excitation in the 4F5/2 and 4F3/2 levels of Nd3+ together with the 4I9/2→ 4F5/2 and 4I9/2→ 4F3/2 bands of Nd3+ in the excitation spectra of Yb3+ ions confirm that energy transfer occurs from Nd3+ to Yb3+. On the other hand, the back transfer from Yb3+ to Nd3+ can be neglected. This conclusion is also in agreement with the vanishing overlap between the Yb3+ emission and Nd3+ absorption. The analysis of the luminescence decay curves obtained after pulsed excitation has been used to further explore energy transfer processes and the interaction mechanism.

Lanthanide DO3A-Complexes Bearing Peptide Substrates: The Effect of Peptidic Side Chains on Metal Coordination and Relaxivity.

Two DO3A-type ligands conjugated to substrates of urokinase (L3) and caspase-3 (L4) via a propyl-amide linker were synthesized and their lanthanide(III) (Ln3+) complexes studied. A model compound without peptide substrate (L2) and an amine derivative ligand mimicking the state after enzymatic cleavage (L1) were also prepared. Proton Nuclear Magnetic Relaxation Dispersion (NMRD) profiles recorded on the gadolinium(III) (Gd3+) complexes, complemented with the assessment of hydration numbers via luminescence lifetime measurements on the Eu3+ analogues, allowed us to characterize the lanthanide coordination sphere in the chelates. These data suggest that the potential donor groups of the peptide side chains (carboxylate, amine) interfere in metal coordination, leading to non-hydrated LnL3 and LnL4 complexes. Nevertheless, GdL3 and GdL4 retain a relatively high relaxivity due to an important second-sphere contribution generated by the strongly hydrophilic peptide chain. Weak PARACEST effects are detected for the amine-derivative EuL1 and NdL1 chelates. Unfortunately, the GdL3 and GdL4 complexes are not significantly converted by the enzymes. The lack of enzymatic recognition of these complexes can likely be explained by the participation of donor groups from the peptide side chain in metal coordination.

Characterization of Ce:CSSO, Pr:CSSO, and co-doped Ce,Pr:CSSO phosphors for aerosol phosphor thermometry

The phosphor Ce:Ca3Sc2Si3O12(Ce:CSSO) was recently investigated for aerosol phosphor thermometry (APT) and shown to be capable of temperature imaging up to at least 1400 K. To date, no thorough characterization of the temperature dependent emission properties of the phosphor has been performed up to 1400 K. Additionally, due to limited sensitivity over certain temperature ranges continuous temperature imaging from 300 to 1400 K was not possible. Here, cerium and praseodymium doped into CSSO are investigated to address these limitations. Singly-doped Ce:CSSO and Pr:CSSO, and co-doped Ce,Pr:CSSO phosphor samples were studied. Emission lifetimes and quenching behavior were characterized in a tube furnace for each phosphor. Results from the singly-doped phosphors were used to interpret the co-doped phosphor results. The phosphor characterization data was used to estimate thermometry performance at temperatures relevant to low-temperature ignition studies in engines. The proposed diagnostic uses a combination of co-doped APT, host-referenced APT, and scattering-referenced APT approaches to increase the range over which high-precision temperature measurements can be made. Characterization results include the first reported measurements of luminescence lifetimes for Ce:CSSO and Pr:CSSO at temperatures up to 1400 K, and the highest reported quenching temperature for a phosphor using 4f5d emission (1230 K for Ce:CSSO). Furnace measurements showed a normalized temperature-sensitivity of % K−1 from room temperature to 1400 K for at least one diagnostic approach using the co-doped Ce,Pr:CSSO phosphor. Estimates suggest that the co-doped Ce,Pr:CSSO phosphor is feasible for APT at temperatures ranging from 300 to 925 K and 1030 to at least 1400 K, with better than 40-K single-shot precision. The performance of Ce:CSSO and Ce,Pr:CSSO are similar throughout the investigated temperature range.

A Fluorous Phosphate for the Effective Extraction of LnIII from Nitrate Media: Comparison with A Conventional Organic Phosphate

ABSTRACT We compare the extraction and separation performance of a newly developed fluorous extractant, tris(4,4,5,5,6,6,7,7,7-nonafluoroheptyl) phosphate (TFP) in a fluorinated diluent perfluorohexane, for trivalent lanthanide ions (LnIII) with a conventional organic extractant, tri-n-butyl phosphate (TBP) in n-octane. Interestingly, the fluorinated extractant TFP exhibits a superior extraction performance for LnIII than the organic extractant TBP, despite the tendency of hydrocarbon fluorination to reduce the extraction performance. Furthermore, the high separation factors among LnIII by TFP suggest that the separation performance of TFP is superior to that of TBP. We proved the superior extraction and separation performance of TFP by comparing the coordination environment of the extracted TFP and TBP complexes, the fluorous phase, and the organic phase. From a microscopic perspective, luminescence lifetime measurements and extended X-ray absorption fine structure spectroscopy revealed the near coordination environment of EuIII in the extracted complex of the extracting phase. Hydrating water scarcely exists in the EuIII-TFP complex, while the EuIII-TBP complex has at least one hydrating water molecule. On the other hand, from a macroscopic perspective, water and nitrate anion transport into the extracting phase during EuIII extraction are revealing. The large amounts of water and NO3 − anions in the organic phase compared to those in the fluorous phase suggest that the extraction of water and NO3 − anions somehow impairs the extraction of EuIII into the organic phase. Hence, TFP in a fluorinated diluent can be used as an alternative extraction and separation system for LnIII.

5-HT1A targeting PARCEST agent DO3AM-MPP with potential for receptor imaging: Synthesis, physico-chemical and MR studies

Contrast enhancement in MRI using magnetization or saturation transfer techniques promises better sensitivity, and faster acquisition compared to T1 or T2 contrast. This work reports the synthesis and evaluation of 5-HT1A targeted PARACEST MRI contrast agent using 1,4,7,10-tetraazacycloDOdecane-4,7,10-triacetAMide (DO3AM) as the bifunctional chelator, and 5-HT1A-antagonist methoxyphenyl piperazine (MPP) as a targeting unit. The multi-step synthesis led to the MPP conjugated DO3AM with 60% yield. CEST-related physicochemical parameters were evaluated after loading DO3AM-MPP with paramagnetic MRI active lanthanides: Gadolinium (Gd-DO3AM-MPP) and Europium (Eu-DO3AM-MPP). Luminescence lifetime measurements with Eu-DO3AM-MPP and computational DFT studies using Gd-DO3AM-MPP revealed the coordination of one water molecule (q = 1.43) with metal-water distance (rM-H2O) of 2.7 Å and water residence time (τm) of 0.23 ms. The dissociation constant of Kd 62 ± 0.02 pM as evaluated from fluorescence quenching of 5-HT1A (protein) and docking score of −4.81 in theoretical evaluation reflect the binding potential of the complex Gd-DO3AM-MPP with the receptor 5-HT1A. Insights of the docked pose reflect the importance of NH2 (amide) and aromatic ring in Gd-DO3AM-MPP while interacting with Ser 374 and Phe 370 in the antagonist binding pocket of 5-HT1A. Gd-DO3AM-MPP shows longitudinal relaxivity 5.85 mM−1s−1 with a water residence lifetime of 0.93 ms in hippocampal homogenate containing 5-HT1A. The potentiometric titration of DO3AM-MPP showed strong selectivity for Gd3+ over physiological metal ions such as Zn2+ and Cu2+. The in vitro and in vivo studies confirmed the minimal cytotoxicity and presential binding of Gd-DO3AM-MPP with 5-HT1A receptor in the hippocampus region of the mice. Summarizing, the complex Gd-DO3AM-MPP can have a potential for CEST imaging of 5-HT1A receptors.

Unmodified Rose Bengal photosensitizer conjugated with NaYF4:Yb,Er upconverting nanoparticles for efficient photodynamic therapy

In photodynamic therapy (PDT), photosensitizer (PS) molecules are irradiated by light to generate reactive oxygen species (ROS), the presence of which subsequently leads to cell death. At present, the modality is limited to the treatment of skin diseases because of the low tissue penetration of visible or ultraviolet light required for producing ROS. To increase tissue penetration and extend the therapeutic possibilities of PDT to the treatment of deep-seated cancer, rare-earth doped nanoparticles capable of up-converting infrared to visible light are investigated. These up-converting nanoparticles (UCNPs) are conjugated with PS molecules to efficiently generate ROS. In this work, we employ hexagonal β-NaYF4:Yb3 + ,Er3 + as UCNPs and Rose Bengal (RB) as PS molecules and demonstrate efficient in vitro PDT using this nanoformulation. Covalent bonding of the RB molecules is accomplished without their functionalization—an approach which is expected to increase the efficiency of ROS generation by 30%. Spectroscopic studies reveal that our approach results in UCNP surface fully covered with RB molecules. The energy transfer from UCNPs to RB is predominantly non-radiative as evidenced by luminescence lifetime measurements. As a result, ROS are generated as efficiently as under visible light illumination. The in vitro PDT is tested on murine breast 4T1 cancer cells incubated with 250 µg ml−1 of the nanoparticles and irradiated with NIR light under power density of 2 W cm−2 for 10 minutes. After 24 hours, the cell viability decreased to 33% demonstrating a very good treatment efficiency. These results are expected to simplify the protocols for preparation of the PDT agents and lead to improved therapeutic effects.