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BackgroundAcute gastrointestinal (GI) illnesses are of the most common problems evaluated by physicians and some of the most preventable. There is evidence of GI pathogen transmission when people are in close contact. The COVID-19 pandemic led to the sudden implementation of widespread social distancing measures in the United States. There is strong evidence that social distancing measures impact the spread of SARS-CoV-2, and a growing body of research indicates that these measures also decrease the transmission of other respiratory pathogens. ObjectiveThis study aims to investigate the impact of COVID-19 social distancing mandates on the GI pathogen positivity rates. MethodsDeidentified GI Panel polymerase chain reaction test results from a routinely collected diagnostic database from January 1, 2019, through August 31, 2020, were analyzed for the GI pathogen positivity percentage. An interrupted time series analysis was performed, using social distancing mandate issue dates as the intervention date. The following 3 target organisms were chosen for the final analysis to represent different primary transmission routes: adenovirus F40 and 41, norovirus GI and GII, and Escherichia coli O157. ResultsIn total, 84,223 test results from 9 states were included in the final data set. With the exception of E coli O157 in Kansas, Michigan, and Nebraska, we observed an immediate decrease in positivity percentage during the week of social distancing mandates for all other targets and states. Norovirus GI and GII showed the most notable drop in positivity, whereas E coli O157 appeared to be least impacted by social distancing mandates. Although we acknowledge the analysis has a multiple testing problem, the majority of our significant results showed significance even below the .01 level. ConclusionsThis study aimed to investigate the impact of social distancing mandates for COVID-19 on GI pathogen positivity, and we discovered that social distancing measures in fact decreased GI pathogen positivity initially. The use of similar measures may prove useful in GI pathogen outbreaks. The use of a unique diagnostic database in this study exhibits the potential for its use as a public health surveillance tool.

The conventional energy transfer pathway in organic lanthanide complexes is purported to be from the excited singlet state of the chromophore to the triplet state and subsequently directly to the emitting state of the trivalent lanthanide ion. In this work, we found that the energy transfer occurs from the triplet state to the nearest energy level, instead of directly to the emitting state of the lanthanide ion. The triplet decay rate for different lanthanide ions follows an energy gap law from the triplet level to the receiving level of the lanthanide ion. Three different categories of complexes were synthesized and inspected using different techniques, demonstrating the universality of our findings. This work renews the insights to conventional findings, highlighting the importance of the energy gap between the triplet state and the nearest lanthanide energy level in optimization of light harvesting. The rationale of ligand design of chromophores should be reconsidered, leading to various applications of lanthanide complexes with enhanced quantum yield and brightness., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Cr 3+ doped near-infrared phosphors hold significant applications and generate considerable research interest. The critical parameter for assessing the strength of the crystal field for Cr 3+ in the Tanabe-Sugano diagram is the boundary value of Dq/B, representing the ratio of crystal field splitting to the Racah parameter B. Nevertheless, there are conflicting values for this parameter, as reported in various studies, such as 2.1, 2.2, and 2.3 for C/B = 4.5-4.8. Moreover, some Cr 3+ doped phosphors with wide-band emissions exhibit a Dq/B value that falls within the region of a contradictory strong field. In this study, we numerically determine the boundary value of Dq/B, which distinguishes between strong and weak fields. The results then demonstrate a dependence on the host material and are correlated with the values of Racah parameters B and C. This work resolves the inconsistency between the boundary values of Dq/B and the emission profile of Cr 3+ , providing researchers with a more profound comprehension of Cr 3+ luminescence.

Undoped Y 2 Ti 2 O 7 exhibits impurity emission bands at low temperatures due to Mn 4+ and Cr 3+ , as established by codoping with these ions. Contrary to a recent report by Wang et al., ACS Appl. Mater. Interfaces 2022 , 14 , 36834-36844, we do not observe Bi 3+ emission in this codoped host, as also is the case for Fe 3+ . The emission reported in that paper as being due to Bi 3+ in fact corresponds to Cr 3+ emission. The Cr 3+ and Mn 4+ emissions are quenched with increasing temperature, so that Mn 4+ emission is scarcely observed above 80 K. We present variable temperature optical data for Y 2 Ti 2 O 7 and this host codoped with Mn, Cr, Fe, and Bi, as well as a theoretical justification of our results.

The responsive control of energy transfer (ET) plays a key role in the broad applications of lanthanide-doped nanomaterials. Photonic crystals (PCs) are excellent materials for ET regulation. Among the numerous materials that can be used to fabricate PCs, chiral nematic liquid crystals are highly attractive due to their good photoelectric responsiveness and biocompatibility. Here, the mechanisms of ET and the photonic effect of chiral nematic structures on ET are introduced; the regulation methods of chiral nematic structures and the resulting changes in ET of lanthanide-doped nanomaterials are highlighted; and the challenges and promising opportunities for ET in chiral nematic structures are discussed., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Orange Eu 2+ -doped phosphors are essential for light-emitting diodes for cornering lights to prevent fatal road accidents at night, but such phosphors require features of high thermal, chemical stability and facile synthesis. This study reports a series of yellow-orange-red emitting SrAl 2 Si 3 ON 6 :Eu 2+ oxynitride phosphors, derived from the SrAlSi 4 N 7 nitride iso-structure by replacing Si 4+ -N 3- with Al 3+ -O 2- . The introduction of a certain amount of oxygen enabled the facile synthesis under atmospheric pressure using the air-stable raw materials SrCO 3 , Eu 2 O 3 , AlN and Si 3 N 4 . SrAl 2 Si 3 ON 6 has a smaller band gap and lower structure rigidity than SrAlSi 4 N 7 (5.19 eV vs 5.50 eV, Debye temperature 719 K vs 760 K), but exhibits higher thermal stability with 100 % of room temperature intensity remaining at 150 °C compared to 85 % for SrAlSi 4 N 7 . Electron paramagnetic resonance, thermoluminescence and density functional theory revealed that the oxygen vacancy electron traps compensated the thermal loss. Additionally, no decrease in emission intensity was found after either being heated at 500 °C for 2 hours or being immersed in water for 20 days, implying both of the thermal and chemical stability of SrAl 2 Si 3 ON 6 :Eu 2+ phosphors. The strategy of oxynitride-introduction from nitride promotes the development of low-cost thermally and chemically stable luminescent materials., (© 2023 Wiley-VCH GmbH.)

The excitation energy transfer (ET) pathway and mechanism from an organic antenna to a lanthanide ion has been the subject of discussion for many decades. In the case of europium (Eu 3+ ), it has been suggested that the transfer originates from the ligand singlet state or a triplet state. Taking the lanthanide complex Eu(TTA) 3 (H 2 O) 2 as an example, we have investigated the spectra and luminescence kinetics, mainly at room temperature and 77 K, to acquire the necessary experimental data. We put forward an experimental and theoretical approach to measure the energy transfer rates from the antenna to different Eu 3+ levels using the Dexter formulation. We find that transfer from the ligand singlet state to Eu 3+ may account for the ET pathway, by combined electric dipole-electric dipole (ED-ED) and ED-electric quadrupole (EQ) mechanisms. The contributions from the triplet state by these mechanisms are very small. An independent systems rate equation approach can effectively model the experimental kinetics results. The model utilizes the cooperative processes that take place on the metal ion and ligand and considers S 0 , S 1 , and T 1 ligand states in addition to 7 F 0,1 , 5 D 0 , 5 D 1 , and 5 DJ (= 5 L 6 , 5 D 3 , 5 D 2 combined) Eu 3+ states. The triplet exchange ET rate is estimated to be of the order 10 7 s -1 . The observation of a nanosecond risetime for the Eu 3+ 5 D 1 level does not enable the assignment of the ET route or the mechanism. Furthermore, the 5 D 1 risetime may be contributed by several processes. Observation of its temperature dependence and also that of the ground-state population can supply useful information concerning the mechanism because the change in metal-ion internal conversion rate has a greater effect than changes in singlet or triplet nonradiative rates. A critical comparison is included for the model of Malta employed in the online software LUMPAC and JOYSpectra. The theoretical treatment of the exchange mechanism and its contribution are now being considered.

The effect of temperature upon the lanthanide luminescence lifetime and intensity has been investigated in toluene solution for the complexes LnPhen(TTA) 3 (Ln = Eu, Sm, Nd, Yb; Phen = 1,10-phenanthroline; TTA = thenoyltrifluoroacetonate). Thermally excited back-transfer to a charge transfer state was found to occur for Ln = Eu and can be explained by lifetime and intensity back-transfer models. The emission intensity and lifetime were also quenched with increasing temperature for Ln = Sm, and the activation energy for nonradiative decay is similar to that for the thermal population of Sm 3+ excited states. Unusual behavior for lifetime and intensity was found for both Ln = Nd, Yb. The usually assumed equivalence of τ/τ 0 = I / I 0 (where τ is lifetime and I is intensity) does not hold for these cases. We infer that for these lanthanide systems the intensity decreases with temperature in the stage prior to population of the luminescent state. The lifetime changes are discussed.

Eu 2+ -activated alkali-lithosilicate phosphors exhibit narrow-band emissions that are attractive to high color-rendition and wide color-gamut displays. The microscopic mechanism behind the small emission bandwidth is not presently understood. Here, we report an explicit calculation of the vibronic process occurring in the narrow-band green emission of Rb 2 Na 2 [Li 3 SiO 4 ] 4 :Eu 2+ . We show that due to the high rigidity of the host material, the structural strain induced by the localized Eu 2+ 4f-5d excitation is distributed among the atoms far beyond the first coordination shell and hence reduces the local structural relaxation around Eu 2+ . The emission bandshape is thus mainly controlled by the coupling of the electronic transition with the phonon modes associated with motions of host constituent atoms, which was further validated by the good agreement of the calculated bandshape with the experiment. The results provide insights into the generation of narrow-band emission and improve our knowledge on electron-phonon coupling of 4f-5d transitions in phosphors.

Emission from the triplet state of an organo-lanthanide complex is observed only when the energy transfer to the lanthanide ion is absent. The triplet state lifetime under cryogenic conditions for organo-lanthanide compounds usually ranges up to tens of milliseconds. The compound LaL1(TTA) 3 reported herein exhibits 77 K phosphorescence observable by the naked eye for up to 30 s. Optical spectroscopy, density functional theory (DFT) and time-dependent DFT techniques have been applied to investigate the photophysical processes of this compound. In particular, on-off continuous irradiation cycles reveal a charging behaviour of the emission which is associated with triplet-triplet absorption because it shows a shorter rise lifetime than the corresponding decay lifetime and it varies with illumination intensity. The discovery of the behaviour of this compound provides insight into important photophysical processes of the triplet state of organo-lanthanide systems and may open new fields of application such as data encryption, anti-counterfeiting and temperature switching., (© 2021. The Author(s).)

Supported by experimental work, wavefunction theory (WFT) calculations and density functional theory (DFT) calculations employing a range of functionals have been performed for two lanthanide complexes to investigate, in gas and solution phases, the representations of frontier orbitals and the orbital transitions between singlet states. The orbital transitions calculated using CASSCF/NEVTP2 served as reference. Functionals with a higher proportion of Hartree-Fock exchange gave better agreement with WFT. The choice of functional is therefore important for understanding the nature of orbital transitions and this is especially relevant in formulating antenna-metal ion energy transfer (ET) mechanisms.

The spontaneous emission rate (SER) of a chromophore in a nanoparticle (NP) is determined by the modification of the electric field by its environment. Previous studies of this local field effect have dispersed NPs in non-chemically interacting media of different refractive index (RI) and measured the emission lifetimes. Unfortunately, the applicable solvents cover only a small range of RI so that the test of a theoretical model is limited. We have utilized the variation of temperature to modify RI so that a more comprehensive test of a model can be achieved. Yttrium aluminium garnet (YAG) NPs doped with Ce 3+ ions were immersed in different alcohols and the lifetime of the electric dipole allowed 5d 1 → 4f 1 transition was measured at different temperatures in each case. In order to clarify and confirm our results we have employed two different dopant concentrations of Ce/Y, near 1.3 at% and 0.13 at%. The Ce 3+ lifetimes were well-fitted to a formula relating the decay rate to the dielectric parameters of the nanocomposite and the volumetric content of the NPs. Two parameters were derived: the SER of the bulk material (found to be effectively constant) and the nonradiative decay rate, which varied as the multiphonon relaxation rate for the more heavily-doped materials. The emission from the YAG:Ce 3+ NPs was attributed to Ce 3+ ions with 8-coordination to oxygen in addition to surface Ce 3+ ions with lower coordination number. The bulk radiative lifetime was determined as 66 ± 3 ns.

Experimental variation of the volume ratio (filling factor: i.e., volume of nanoparticles (NPs) compared with that of medium) of nanocomposite materials with doped lanthanide ions demonstrates that it has a significant affect upon local field effects. Lanthanum orthophosphate NPs are doped with Eu 3+ and/or Tb 3+ and immersed in organic solvents and lead borate glasses for Tb 3+ 5 D 4 lifetime measurements. For media with a refractive index (n med ) less than that of LaPO 4 (n np = 1.79), the 5 D 4 emission decay rate increases with increasing volume ratio of the NPs, whereas for n med > 1.79, the decay rate decreases with increasing volume ratio. Fitting with the model of Pukhov provides an estimation of the radiative lifetime of 5 D 4 and the quantum yield. Energy transfer (ET) from Tb 3+ to Eu 3+ occurs in co-doped LaPO 4 NPs with excitation into a Tb 3+ absorption band. The ET rate is independent on n med and the energy transfer efficiency decreases with an increase in n med . The behavior of ET rate with regard to the local field is consistent with the Dexter, but not Förster, equation for ET rate involving the electric dipole-electric dipole mechanism. This has consequences when using the spectroscopic ruler approach to measure distances between donor-acceptor chromophores., (© 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A reversible and sensitive pH probe DPE-Rh operates by Förster resonance energy transfer from 1,2-diphenylethyne (DPE) to Rhodamine B (Rh). In the presence of H + , the spirolactam ring of the Rhodamine B unit was opened and this resulted in ca. 1000-fold enhancement of fluorescence intensity with linear change over the pH range of 2.0 to 5.5. The Förster resonance energy transfer offered this probe an effective excitation-emission wavelength shift of around 240 nm with about 100 % quenching of the donor emission. The response of the sensor is tolerant towards a wide range of metal ions and the sensing mechanism was deduced by 1 H NMR spectrometry. This FRET-based molecule not only provides a sensitive pH probe, but also suggests an effective strategy to eliminate the interference of excitation light., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Although lanthanide double-decker complexes with hetero-macrocyclic ligands as functional luminescent and magnetic materials have promising properties, their inferior water solubility has negated their biomedical applications. Herein, four water-soluble homoleptic lanthanide ( Ln   =   Gd , Er , Yb and La ) sandwiches with diethylene-glycol-disubstituted porphyrins ( DD ) are reported, with their structures proven by both quantum chemical calculations and scanning tunneling microscopy. Our findings demonstrate that the near-infrared emission intensity and singlet oxygen ( 1 O 2 ) quantum yields of YbDD and GdDD in aqueous media are higher than those of the reported capped lanthanide monoporphyrinato analogues, YbN and GdN ; the brightness and luminescence lifetime in water of YbDD are greater than those of YbN . This work provides a new dimension for the future design and development of molecular theranostics-based water-soluble double-decker lanthanide bisporphyrinates., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest.

The energy transfer (ET) between Tb 3+ and Eu 3+ is investigated experimentally and with available theoretical models in the regime of high Tb 3+ concentrations in ≈30 nm LaPO 4 nanoparticles at room temperature. The ET efficiency approaches 100% even for lightly Eu 3+ -doped materials. The major conclusion from the use of pulsed laser excitation and switched-off continuous wave laser diode excitation is that the energy migration between Tb 3+ ions, situated on La 3+ sites with ≈4 Å separation, is not fast. The quenching of Tb 3+ emission in singly doped LaPO 4 only reduces the luminescence lifetime by ≈50% in heavily doped samples. Various theoretical models are applied to simulate the luminescence decays of Tb 3+ and Tb 3+ , Eu 3+ -doped LaPO 4 samples of various concentrations and the transfer mechanism is identified as forced electric dipole at each ion., Competing Interests: The authors declare no conflict of interest.

Herein, we have investigated spectral structure and intensity changes in a bimetallic lanthanide complex comprising La3+ and Eu3+, with the ions coordinated to silent and antenna ligands, when their positions are interchanged. Comparison of the fluorescence decay of a ligand in the presence and absence of La3+ has enabled internal nonradiative decay rates to be determined. The effects upon Eu3+ emission spectra resulting from changes in its environment at a distance of ∼10 Å, and upon changing from the solid state to solution, were also investigated. Conclusive results to these investigations were achieved from the electronic excitation spectra, emission spectra and emission decay measurements of cyc-phen, cycLn1-phLn2, cycLn-phen and phLn (Ln = La, Eu; cyc = substituted 1,4,7,10-tetrazacyclododecane; phen = 1,10-phenanthroline; ph = phen(pdtc)3, pdtc = pyrrolidine-1-carbodithioate) recorded in the solid state, at 298 K and ∼10 K, and in solution. Ligand fluorescence was observed in all cases at room temperature, and phosphorescence was observed at 77 K, except for cyc-phen. The phosphorescence lifetimes of the La3+ complexes extend up to 180 ms. Our results support the concept that the lowest excited states of the complexes are localized on individual ligands, in the present case phen, rather than delocalized over the entire molecule.

The optical thermometer has shown great promise for use in the fields of aeronautical engineering, environmental monitoring and medical diagnosis. Self-referencing lanthanide thermo-probes distinguish themselves because of their accuracy, calibration, photostability, and temporal dimension of signal. However, the use of conventional lanthanide-doped materials is limited by their poor reproducibility, random distance between energy transfer pairs and interference by energy migration, thereby restricting their utility. Herein, a strategy for synthesizing hetero-dinuclear complexes that comprise chemically similar lanthanides is introduced in which a pair of thermosensitive dinuclear complexes, cycTb-phEu and cycEu-phTb, were synthesized. Their structures were geometrically optimized with an internuclear distance of approximately 10.6Å. The sensitive linear temperature-dependent luminescent intensity ratios of europium and terbium emission over a wide temperature range (50-298K and 10-200K, respectively) and their temporal dimension responses indicate that both dinuclear complexes can act as excellent self-referencing thermometers. The energy transfer from Tb 3+ to Eu 3+ is thermally activated, with the most important pathway involving the 7 F 1 Eu 3+ J -multiplet at room temperature. The energy transfer from the antenna to Eu 3+ was simulated, and it was found that the most important ligand contributions to the rate come from transfers to the Eu 3+ upper states rather than direct ligand-metal transfer to 5 D 1 or 5 D 0 . As the first molecular-based thermometer with clear validation of the metal ratio and a fixed distance between the metal pairs, these dinuclear complexes can be used as new materials for temperature sensing and can provide a new platform for understanding the energy transfer between lanthanide ions., Competing Interests: The authors declare that they have no conflict of interest.

The Ce 3+ ion in Cs 2 NaCe(NO 2 ) 6 (I), which comprises the unusual T h site symmetry of the Ce(NO 2 ) 6 3- ion, demonstrates the largest Ce-O Stokes shift of 8715 cm -1 and the low emission quenching temperature of 53 K. The activation energy for quenching changes with temperature, attributed to relative shifts of the two potential energy curves involved. The splitting of the Ce 3+ 5d 1 state into two levels separated by 4925 cm -1 is accounted for by a first principles calculation using the crystal structure data of I. The NO 2 - energy levels and spectra were investigated also in Cs 2 NaLa(NO 2 ) 6 and modelled by hybrid DFT. The vibrational and electronic spectral properties have been thoroughly investigated and rationalized at temperatures down to 10 K. A comparison of Stokes shifts with other Ce-O systems emphasizes the dependence upon the coordination number of Ce 3+ .

Many treatments of energy transfer (ET) phenomena in current literature employ incorrect arguments and formulae and are not quantitative enough. This is unfortunate because we witness important breakthroughs from ET experiments in nanoscience. This review aims to clarify basic principles by focusing upon Förster-Dexter electric dipole-electric dipole (ED-ED) ET. The roles of ET in upconversion, downconversion and the antenna effect are described and the clichés and simple formulae to be avoided in ET studies are highlighted with alternative treatments provided.

The crystal structure and electronic spectra of the T h symmetry hexanitritoytterbate(III) anion have been studied in Cs 2 NaY 0.96 Yb 0.04 (NO 2 ) 6 , which crystallizes in the cubic space group Fm3̅. The emission from Yb 3+ can be excited via the NO 2 - antenna. The latter electronic transition is situated at more than twice the energy of the former, but at room temperature, one photon absorbed at 470 nm in the triplet state produces no more than one photon emitted. Some degree of quantum cutting is observed at 298 K under 420 nm excitation into the singlet state and at 25 K using excitation into either state. The quantum efficiency is ∼10% at 25 K. The energy level scheme of Yb 3+ has been deduced from excitation and emission spectra and calculated by crystal field theory. New improved energy level calculations are also reported for the Cs 2 NaLn(NO 2 ) 6 (Ln = Pr, Eu, Tb) series using the f- Spectra package. The neat crystal Cs 2 NaYb(NO 2 ) 6 has also been studied, but results were unsatisfactory due to sample decomposition, and this chemical instability makes it unsuitable for applications.

A cell-permeable ytterbium complex shows reversible binding with Hg 2+ in aqueous solution and in vitroby off-on visible and NIR emission. The fast response and 150 nM sensitivity of Hg 2+ detection is based upon FRET and the lanthanide antenna effect. The reversible Hg 2+ detection can be performed in vitro, and the binding mechanism is suggested by NMR employing the motif structure in a La complex and by DFT calculations.

Aerosols affect the insolation at ground and thus the Aerosol Optical Depth (AOD, a measure of aerosol pollution) plays an important role on the variation of the Physiological Equivalent Temperature (PET) at locations with different aerosol climatology. The aerosol effects upon PET were studied for the first time at four East Asian cities by coupling a radiative transfer model and a human thermal comfort model which were previously well evaluated. Evident with the MODIS and AERONET AOD observations, the aerosol pollution at Beijing and Seoul was higher than at Chiayi (Taiwan) and Hong Kong. Based on the AERONET data, with background AOD levels the selected temperate cities had similar clear-sky PET values especially during summertime, due to their locations at similar latitudes. This also applied to the sub-tropical cities. Increase in the AOD level to the seasonal average one led to an increase in diffuse solar radiation and in turn an increase in PET for people living in all the cities. However, the heavy aerosol loading environment in Beijing and Seoul in summertime (AODs > 3.0 in episodic situations) reduced the total radiative flux and thus PET values in the cities. On the contrary, relatively lower episodic AOD levels in Chiayi and Hong Kong led to strong diffuse and still strong direct radiative fluxes and resulted in higher PET values, relative to those with seasonal averaged AOD levels. People tended to feel from "hot" to "very hot" during summertime when the AOD reached their average levels from the background level. This implies that in future aerosol effects add further burden to the thermal environment apart from the effects of greenhouse gas-induced global warming. Understanding the interaction between ambient aerosols and outdoor thermal environment is an important first step for effective mitigation measures such as urban greening to reduce the risk of human heat stress. It is also critical to make cities more attractive and enhancing to human well-being to achieve enhancing sustainable urbanization as one of the principal goals for the Nature-based Solutions., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Samples of the Ca 3 Sc 2 Si 3 O 12 (CSS) host singly doped with Eu 2+ or Yb 3+ , doubly doped with Eu 2+ and Yb 3+ , and triply doped with Ce 3+ , Eu 2+ and Yb 3+ were synthesized by a sol-gel combustion process under reducing conditions. Unlike previous reports of Eu 2+ →Yb 3+ energy transfer in other systems, the energy transfer is resonant in the CSS host and the transfer efficiency reaches 100 % for lightly doped samples. The transfer mechanism is multipolar rather than electron transfer for the sample compositions employed herein. The emission intensity of Yb 3+ is further enhanced by co-doping with Ce 3+ in addition to Eu 2+ . The quantum efficiencies of the doped materials range between 9 % and 93 %., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The downshifting from Ce(3+) blue emission to Yb(3+) near-infrared emission has been studied in the garnet host Ca2.8-2xCe0.1YbxNa0.1+xSc2Si3O12 (x = 0-0.36). The downshifting does not involve quantum cutting, but one incident blue photon is transferred from Ce(3+) to Yb(3+) with an energy transfer efficiency up to 90% when x = 0.36 for the Yb(3+) dopant ion. For x ≤ 0.15, a multiphonon-assisted electric dipole-electric quadrupole mechanism of energy transfer dominates, while for the highest concentration of Yb(3+) employed, the electron transfer mechanism is confirmed. A temperature-dependent increase of the Ce(3+) → Yb(3+) energy transfer rate does not exclusively indicate the electron transfer mechanism. The application of the material to solar energy conversion is indicated.

Analyses of the crystal field energy levels of the series LaCl3:Ln(3+) using a semiempirical Hamiltonian shows that only five ions (Pr, Nd, Pm, Dy, Ho) meet the criteria to avoid overfitting of the atomic part. A new parameter (SNES) has been introduced to represent the strength of the normalized electrostatic repulsion for these ions. This parameter varies linearly (R(2)adj = 0.9994, N = 5) with the reciprocal of the radius of the tripositive lanthanide ion, as expected from the form of repulsive Coulomb interaction. The Slater parameters from the crystal field analyses, F(k)(corr) (i.e., corrected for the effects of the two-particle component of the three-body operator associated with the T(2) parameter), exhibit an exponential variation with the number of electrons, n, in 4f(n). This is explained by reference to the radial part of a hydrogen-like wave function. The ratio of F(k)(corr) with the ab initio free ion Slater parameter F(k)(ab initio) varies linearly with n. Fitted parameters F(k)(corr: free ion) from the free ion data for Pr(3+) and Nd(3+) show that the corresponding ab initio values are between 14 and 27% too high. The spin-orbit coupling constant from crystal field analyses (ζ4f) exhibits a quartic variation with atomic number, and the ratio ζ4f/ζ4f(ab initio) follows an exponential growth model with n. The results serve to confirm the hypothesis that smooth trends can be observed across the Ln(3+) series for the fitted parameters despite the fact that the majority of experimental data is lacking.

Ten substituted benzoate complexes of Pr(3+) of the type [Pr(XC6H4COO)3(H2O)n(DMF)m]p·(DMF)q (X = OCH3, NO2, OH, F, Cl, NH2) have been synthesized, and for eight of these crystallographic data are available. The electronic absorption and emission spectra of the complexes have been recorded and interpreted at temperatures down to 10 K for transitions involving the (3)P0 and (1)D2 J-multiplet terms. Generally, the electron-withdrawing groups X in the benzoate moiety lead to higher (3)P0 energy than electron-donating groups. Empirical relations have been found between the energies of the (3)P0 and (1)D2(1) levels and the Hammett sigma constants for substituents and the unit cell volume per Pr(3+) ion. The latter relationship is indicative of a correlation between the electronic state energy and the ligand dipole polarizability. This has been confirmed by reference to literature data for the LaX3:Pr(3+) systems, so that the ligand dipole polarizability is a key factor in determining the nephelauxetic shifts of 4f(N) ions in crystals.

Some features of the interaction of the 4f(N) configuration of tripositive lanthanide ions (Ln(3+)) with excited configurations have been investigated. The calculated barycenter energies of the same parity 4f(N-1)6p, 4f(N+1)5p(5), and 4f(N-1)5f configurations for Ln(3+), relative to those of 4f(N), are fitted well by exponential functions. The 4f(N) barycenter energies of Ln(3+) in Y3Al5O12/Ln(3+) lie in the band gap, with the exceptions of Tb(3+) and Yb(3+), where they are situated in the conduction and valence bands, respectively. The configuration interaction parameters α, β, and γ, which are fitted in the usual phenomenological Hamiltonian to calculate the crystal field energies of Ln(3+), exhibit quite variable magnitudes in the literature due to incomplete energy level data sets, energy level misassignments and fitting errors. For LaCl3/Ln(3+), 83% of the variation of α and 50% of that for β can be explained by the change in the difference in barycenter energy with the predominant interacting configuration. The parameter γ is strongly correlated with the Slater parameter F(2) and is not well-determined in most calculations. The values of the electrostatically correlated spin-other orbit parameter P(2) vary smoothly across the Ln(3+) series with the barycenter difference between the 4f(N) and 4f(N-1)5f configurations. Calculations of the P(k) (k = 2, 4, and 6) values for Pr(3+) show that 4f → nf excitations only account for ∼65% of the value of P(2) for LaCl3/Pr(3+) and 35% of that in Y3Al5O12/Pr(3+). The role of the ligand is therefore important in determining the value, and a discussion is included of the present state of configuration-interaction-assisted crystal field calculations. Further progress cannot be made in the above areas until more reliable and complete energy level data sets are available for the Ln(3+) series of ions in crystals.

The well-known nephelauxetic series of ligands describes the change in interelectronic repulsion of the central metal ion, which is reduced on going from the vapor to crystalline state. This study examines the trends and quantifies the mechanism of this series for the lanthanide ion Pr(3+), with the 4f(2) electronic configuration. A new and concise measurement by a single parameter, σee, is introduced to quantify the overall strength of interelectronic repulsion, as the alternative to the Slater parameters, F(k) (k = 2, 4, 6). Energy parameters have been derived from the literature electronic spectra of Pr(3+), in the free ion and in various crystalline hosts, with new calculations in some cases. It is found that at least the first 12 of the 13 multiplet terms of Pr(3+) must be well-determined to obtain reliable parameter values. The shifts of various energy levels for changes in the Slater parameters are not uniform in direction. For the various Pr(3+) solid-state systems, the change in σee is only up to ∼5%, with the magnitude of σee in the order F(-) > Cl(-) > O(2-) ≈ Br(-) > C, and decreasing with lower coordination number of the ligand. The decreases of the Slater parameters from the free ion values are reasonably estimated by considering the dielectric constant of the medium. In particular, the magnitude of σee (and of the spin-orbit coupling constant) is proportional to the polarizability of the ligand for F(-), Cl(-), O(2-), and Br(-). The data point scatter for oxide systems is accounted for by considering the individual ligand bond distances. A fair estimation of nephelauxetic effects can be made from some luminescence transition energies, by contrast with Eu(3+) systems where crystal field effects also play a major role. In conclusion, the nephelauxetic effect of Pr(3+) is due to the polarization of the ligand by one 4f electron, and the interaction of the other electron with the induced multipolar moments, of which the dipole moment dominates.

Tripositive europium attracts wide interest in diverse fields such as phosphors, sensors, and time-gated bioimaging agents based upon its optical emission spectra. Some inaccurate descriptions of these spectra are being amplified throughout the literature. In this tutorial review the background of electronic states, energy levels and transition intensities is provided as a pre-requisite for clarifying these misconceptions. The topics discussed encompass the electric dipole nature of intraconfigurational 4f electronic transitions, the use of europium as site symmetry and centrosymmetry probe, as well as an indicator of nephelauxetic effects. The frequently mis-used term Stokes shift is also clarified and alternative terms are given for the situations where it is incorrectly applied.

Relationships involving the interelectronic repulsion parameters, F(k) (k = 2, 4, 6), the spin-orbit coupling constant, ζf, and J-mixing, with the (5)D0-(7)F0 energy, E, have been investigated for Eu(3+) using various approaches. First, the linear relationship between E and the (7)F1 splitting (or the second rank crystal field parameter) is shown to be applicable not only to glasses but also to solid-state crystalline systems with Eu(3+) site symmetry of C2, C2v, or lower. In these cases, the change in (5)D0-(7)F0 energy is mainly due to the J-mixing effect of (7)F(J) (J = 2, 4, 6: most notably J = 2) which depresses (7)F0, whereas the (5)D0 energy is relatively constant. The (5)D0-(7)F0 energy also depends upon certain energy parameters in the Hamiltonian, in particular, F(k) and ζf. Model calculations show that increase in F(4) or F(6) produces an increase in E, whereas increase in F(2) produces a decrease in E. An increase in ζf produces a decrease in E. These findings are rationalized. Most previous 4f(6) crystal field calculations have only considered the F and D terms of Eu(3+) so that the Slater parameters are not well-determined. More reliable energy level data sets and crystal field calculations for Eu(3+) with fluoride, oxide, or chloride ligands have been selected, and certain of these have been repeated since most previous calculations have errors in matrix elements. The fitted Slater parameters have been corrected for the effects of three-body Coulomb interactions. Some systems do not follow the ligand trend F ~ O > Cl for Slater and spin-orbit parameters. From the limited data available, the average values of the corrected Slater parameters are greater for fluoride compared with chloride ligands, but the differences are comparable with the standard deviations of the parameters. There is no clear nephelauxetic series for these three types of ligands, with respect to spin-orbit coupling. Previous correlations of E with various parameters are of limited value because the (5)D0-(7)F0 energy difference not only depends upon the F(k) and ζf parameters but in addition is sensitive to the importance of J-mixing for low symmetry systems.

Although the optical spectra of LnCl(6)(3-) systems are complex, only two crystal field parameters, B(40) and B(60), are required to model the J-multiplet crystal field splittings in octahedral symmetry. It is found that these parameters exhibit R(-5) and R(-7) dependence, respectively, upon the ionic radius Ln(3+)(VI), but not upon the Ln-Cl distance. More generally, the crystal field strengths of LnX(6) systems (X = Br, Cl, F, O) exhibit linear relationships with ligand electronegativity, charge transfer energy, and fractional ionic character of the Ln-X bond.

The luminescence spectra of Eu(3+) doped in a series of double perovskite lattices Ba(2)LnMO(6) (Ln = Y, Gd; M = Nb, Ta) have been recorded at room temperature and 10 K. Together with FT-IR and FT-Raman spectra and aided by DFT vibrational energy calculations, assignments have been made for the crystal field levels of the (5)D(J) (J = 0,1) and (7)F(J) (J = 0-2) multiplets. The luminescence spectra are consistent with monoclinic symmetry of these systems. The crystal field parameters from the fitting of the energy level data set of Ba(2)YNbO(6):Eu(3+) enable the crystal field strength to be calculated, and the order of magnitude is Cl(-) < O(2-) < F(-) for the EuX(6)(n-) (n = 6 for halogen, 9 for oxide) moieties. For these systems, an empirical linear relationship between crystal field strength and electronegativity of ligand X has been found. By contrast, the nephelauxetic series from the depression of the Slater parameter F(2) is Cl(-) ≈ O(2-) > F(-) > free ion for these systems.

Three europium complexes with the terdentate N-donor ligand 2,6-bis(1H-pyrazol-3-yl)pyridine (L) have been synthesized, and their crystal structures have been determined. The ligand/metal ratios in these complexes are 3, 2, and 1. The photophysical properties of the complexes indicate more efficient ligand sensitization of europium emission for the homoleptic complex.

The luminescence spectra of Eu(3+) at a T(h) point-group site in the hexanitritolanthanate systems Cs(2)NaEu((14)NO(2))(6), Cs(2)NaEu((15)NO(2))(6), Rb(2)NaEu((14)NO(2))(6), Cs(2)LiEu((14)NO(2))(6), and Cs(2)NaY((14)NO(2))(6):Eu(3+) have been recorded between 19,500 and 10,500 cm(-1) at temperatures down to 3 K. The spectra comprise magnetic-dipole-allowed zero phonon lines, odd-parity metal-ligand vibrations, internal anion vibrations, and lattice modes, with some weak vibrational progressions based upon vibronic origins. With the aid of density functional theory calculations, the vibrational modes in the vibronic sidebands of transitions have been assigned. The two-center transitions involving NO(2)(-) stretching and scissoring modes are most prominent for the (5)D(0) → (7)F(2) hypersensitive transition. The onset of NO(2)(-) triplet absorption above 20,000 cm(-1) restricts the derived Eu(3+) energy-level data set to the (7)F(J) (J = 0-6) and (5)D(0,1) multiplets. A total of 21 levels have been included in crystal-field energy-level calculations of Eu(3+) in Cs(2)NaEu(NO(2))(6), using seven adjustable parameters, resulting in a mean deviation of ~20 cm(-1). The comparison of our results is made with Eu(3+) in the double nitrate salt. In both cases, the fourth-rank crystal field is comparatively weaker than that in europium hexahaloelpasolites.

Successful doping of Eu3+ ions into ZnO nanocrystals has been realized by using a low temperature wet chemical doping technique. The substitution of Eu3+ for Zn2+ is shown to be dominant in the Eu-doped ZnO nanocrystals by analyzing the X-ray diffraction patterns, transmission electron microscopy images, Raman and selectively excited photoluminescence spectra. Measurement of the luminescence from the samples shows that the excited ZnO transfers the excited energy efficiently to the doped Eu3+ ions, giving rise to efficient emission at red spectral region. The red emission quantum yield is measured to be 31% at room temperature. The temperature dependence of photoluminescence and the photoluminescence excitation spectra have also been investigated, showing strong energy coupling between the ZnO host and Eu3+ ions through free and bound excitons. The result indicates that Eu3+ ion-doped ZnO nanocrystals are promising light-conversion materials and have potential application in highly distinguishable emissive flat panel display and LED backlights.

The Pr(3+) ion in Cs(2)NaPr(NO(2))(6) is situated at a site of T(h) symmetry with 12-coordination to O atoms of bidentate nitrito groups. First-principles calculations of the vibrational modes of the complex were carried out using the density functional theory with the generalized gradient approximation Perdew-Burke-Ernzerhof exchange-correlation functional. The calculations that treated the Pr(3+) 4f electrons as valence electrons showed better agreement with the experimental vibrational assignments compared with those treating the 4f electrons a part of the inner core. The (1)D(2) → (3)H(4) emission spectra of Cs(2)NaPr(NO(2))(6) at 7 K enabled assignments to be made for the crystal-field (CF) levels of the ground-state multiplet. The emission of the dilute system Cs(2)NaY(NO(2))(6):Pr(3+) was dominated by NO(2)(-) triplet emission, which was quenched at elevated temperatures by energy transfer to trace Eu(3+) impurity. From magnetic dipole calculations and the vibronic fingerprint, detailed assignments are given for the complex 10 K electronic absorption spectrum of Cs(2)NaPr(NO(2))(6) between 3940 and 18800 cm(-1), and the derived Pr(3+) 4f(2) energy-level data set has been fitted by calculation. By comparison with Cs(2)NaPrCl(6), the fourth-order CF parameter in Cs(2)NaPr(NO(2))(6) is relatively small so that interaction with a 4fnp configuration is not important. From the NO(2)(-) absorption bands above 20,000 cm(-1), the N-O bond length change upon excitation is small, whereas the angle O-N-O opens by more than 10° in the triplet state. By contrast to the NO(2)(-) internal vibration frequencies, which except for the wagging mode show only minor changes with the environment, the triplet-state energy shows a linear decrease with an increase of the lanthanide (Ln(3+)) ionic radius in Cs(2)NaLn(NO(2))(6). Using the eigenvectors from the energy-level fit, the variation of the inverse magnetic susceptibility with temperature has been calculated between 1 and 100 K and the values are somewhat lower than those from experiment.

The low-temperature absorption and excitation spectra of interconfigurational 4f-5d transitions of Tb(3+) in a cubic fluoride host demonstrate the appearance of a first-order linear Jahn-Teller effect for the high-spin excited states of the excited electronic configuration 4f(7)5d involving 5d t(2g) orbitals. The τ(2g) mode is observed to be responsible for the splitting of the otherwise degenerate 5d t(2g) orbitals., (© 2011 American Chemical Society)

The emission and excitation spectra of Ce(3+) and Pr(3+) doped into the cubic host Cs(2)NaYF(6) have been recorded at room temperature and ∼10 K using synchrotron radiation. The two 5d(1) T(2g) states of Ce(3+) have been located from the excitation spectra, whereas the E(g) state is placed above the host band gap. Decay measurements of the 5d(1) → 4f(1) Ce(3+) emission, and spectra collected using selective excitation, indicate the occupation of more than one type of site by Ce(3+) in this host lattice. By contrast, the location of features in the 4f(1)5d(1) → 4f(2) emission of Pr(3+) is independent of the excitation wavelength. Assignments are presented for some of the 4f(1)5d(1) levels and for the Pr(3+)-F(-) charge transfer band. The 5d emission lifetimes for Ce(3+) and Pr(3+) in the Cs(2)NaYF(6) host are 42 and 29 ± 1 ns, respectively, and are not temperature-dependent., (© 2011 American Chemical Society)

Objective: To evaluate injection-site reactions and serum antibody titers in cattle vaccinated with a clostridial vaccine administered SC or via needle-free transdermal injection., Animals: Sixteen 11-to 12-month-old Herefords., Procedures: Cattle in 2 groups were vaccinated on days 0 and 28 with a commercially available multivalent clostridial vaccine administered SC or transdermally Injection sites and serum antibody titers were evaluated at several time points after vaccination. Serum antibody titers against Clostridium perfringens beta toxin, Clostridium novyi alpha toxin, and Clostridium septicum alpha toxin were determined with an ELISA; Clostridium sordellii lethal toxin titers were determined with a toxin neutralization assay., Results: Firm injection site swellings developed in cattle vaccinated via either route; however, at several observation times, swellings were significantly smaller in cattle vaccinated transdermally. Serum titers against C perfringens beta toxin and C septicum alpha toxin did not differ significantly between groups after vaccination; serum titers against C novyi alpha toxin were not significantly different between groups, except on days 10 and 56, when they were significantly higher in cattle vaccinated SC. Titers against C sordellii lethal toxin were significantly higher in cattle vaccinated SC on several days after vaccination, but titers were not significantly different after day 49., Conclusions and Clinical Relevance: Transdermal vaccination of cattle resulted in serum antibody titers that were similar to those induced via SC vaccination and caused injection-site reactions that were significantly smaller. Transdermal vaccination may be an effective technique for vaccinating cattle against clostridial diseases while minimizing local reactions that often develop after clostridial vaccination.

A multiphoton process to the conduction band of the insulator Er2O3 is reported, which occurs in vacuum under near infrared excitation. The enormous upconversion intensity is two orders of magnitude greater than that in air, and also the intensity ratio for green and red emission bands is inverted. The mechanism is probed by experiments of laser power dependence, cathodoluminescence, photoconductivity dependence and chemical dilution, and it involves cross-relaxation energy transfer upconversion of erbium ions to reach the conduction band. The upconversion color is tunable by changes in pressure, laser diode intensity and wavelength, or dopant ion concentration.

The electronic absorption spectra of single crystals of Cs(2)NaHoF(6) have been recorded in the spectral region between 4700 and 42000 cm(-1) at temperatures down to 10 K. The structure in the (5)I(8) → (5)I(J) (J = 7-4), (5)F(J) (J = 5-1), (5)S(2), (5)G(J) (J = 4-6), (3)K(J) (J = 7, 8) transitions has been analyzed and assigned. The emission spectra (5)S(2) → (5)I(J) (J = 6-8) and (5)G(4) → (5)I(J) (J = 5-7), (5)F(5) have also been recorded at 10 K for crystals of Cs(2)NaHoF(6) and partly also for samples of Cs(2)NaHoF(6):Yb(3+). The spectra comprise magnetic dipole zero phonon lines and electric dipole allowed one-phonon vibronic sidebands. From the detailed interpretation of the emission and absorption spectra, aided by a clear understanding of the vibrational behavior of the HoF(6)(3-) moiety and by magnetic dipole intensity calculations, a data set of 59 energy levels spanning 17 multiplet terms was derived. Crystal field calculations were then performed using a 4f(10) basis, as well as including the configuration interaction with a p-electron configuration. The latter calculation, which employed 14 parameters, gave better agreement with experiment and the mean deviation was 13.5 cm(-1). A comparison with the energy level fittings for Cs(2)NaHoCl(6) has been included. The crystal field parameters for the fluoro- and chloro-systems followed empirically predicted ratios.

Published two photon excitation (TPE) intensities for the cubic elpasolite systems Cs(2)NaTbX(6) (X = Cl, F) have been simulated by a calculation of two photon absorption (TPA) intensities which takes into account electric dipole transitions involving the detailed crystal-field structure of 4f(7)5d intermediate states, as well as the interactions of the 4f(7) core with the d-electron. The intensity calculation employed parameters from an energy level calculation which not only presented an accurate fit, but also yielded parameters consistent with those from other lanthanide ions. The calculated intensities were used to confirm or adjust the previous assignments of energy levels, resulting in some minor revisions. Generally, the TPA intensity simulations were in better agreement with experimental data for the fluoride, rather than the chloride, system and possible reasons for this are given.

We report on multiphoton white-light upconversion in vacuum for Pechini synthesis Yb(3)Al(5)O(12) (YbAG) and combustion synthesis (Yb,Y(2))O(3) nanopowders under IR excitation. Their intense white-light upconversion is attributed to charge transfer luminescence superimposed upon a broadband emission. Unlike common nanoscale phosphors, which show low luminescence efficiency, the intensity of white-light upconversion for nanopowders is similar to that of their bulk counterparts. The luminary efficacy of the upconversion is estimated to be 10-15 lm W(-1), and the Commission Internationale d'Eclairage (CIE) coordinates can be widely tuned by the excitation power, pressure, and codoping ratio. The nano-YbAG sample exhibits a longer buildup time for emission, a higher excitation threshold, and a wider CIE range than the oxide nanopowders.