Electrochemical Ce(III)/Ce(IV) Redox Behavior and Ce Oxide Nanostructure Recovery over Thio-Terpyridine-Functionalized Au/Carbon Paper Electrodes.

Understanding the electrochemical behaviors of Ce(III)/Ce(IV) ions is essential for better treatment, separation, and recycling of lanthanide (Ln) and actinide (An) elements. Herein, electrochemical redox behavior and interconversion of Ce(III)/Ce(IV) ions and their recoveries were demonstrated over newly developed thio-terpyridine-functionalized Au-modified carbon paper electrodes in acidic and neutral electrolytes. Cyclic voltammetry and amperometry were performed for the electrodes with and without thio-terpyridine functionalization. Ce oxide nanostructure recovery was successfully conducted by amperometry, and the electrodeposited nanostructured Ce materials were fully characterized by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction crystallography, and X-ray photoelectron spectroscopy. Geometry optimization and the electronic energy state calculations were conducted by density functional theory at the B3LYP/GENECP level for the complexes of Ce(III) and Ce(IV) ions with the thio-terpyridine in an aqueous state. The present unique results provide valuable information on understanding redox behaviors of Ln and An ions for their recycling and treatment processes.

Blue-Light-Emitting Photostable Hybrid Films for High-Efficiency Large-Area Light Converter and Photonic Applications.

A blue fluorophore of Schiff base zinc complex is prepared by a hydrolysis-free solution-based synthetic method. Under ultraviolet (UV) excitation, the complex produces blue emission with a quantum yield ( Q) of 42.6% in methylene chloride and 24.0% in standalone powder form. Quantum mechanical calculations show that the blue emission is generated by the change in the chemical state of the ligand associated with the complexation with Zn cations. Thin films of Zn complexes incorporated in polymethylmethacrylate (PMMA) and cellulose acetate butyrate (CAB) polymers are also prepared by dispersing the complexes into the polymer matrices. These hybrid polymer films exhibit several notable features, particularly enhanced luminescence efficiency (with maximum Q of 85.8% for PMMA and 30.0% for CAB) and scalability for fabrication over a large area while retaining the original properties of the host polymers. Light-emitting diodes are also fabricated using the CAB hybrid thin films, and they show a Q of 43.2% with excellent photostability. The complex and its hybrid films demonstrate their great potential for such applications as UV-to-blue conversion devices in photoelectronics, solar-cell concentrators, solid-state lighting and display, and greenhouse agriculture.

White and Tunable Emission from and Rhodamine B Detection by Modified Zinc Oxide Nanowalls.

To gain better optical and optoelectrical properties, doping trivalent lanthanide cations into host materials is a very attractive approach in nanoscience. Here, we use a transparent conducting oxide, zinc oxide, as the host material to directly embed trivalent terbium cations without the need for any postgrowth treatment, and we investigate the photophysical effect of the dopant. Trivalent Tb cations embedded in ZnO nanowalls produce hypersensitive green emission (at 545 nm, corresponding to the 5D4 → 7F5 transition) and convert the emission color of ZnO from yellow into white. Evidently, the photoluminescence emission intensity of Tb(III) is further increased by close to 10-fold due to the plasmonic effect introduced by noble metal (Ag and Pt) nanoparticles. The characteristic Tb(III) emission is found to be tunable from white to red and is examined for its potential chemosensing application for rhodamine B involving a plausible cascade energy transfer mechanism from ZnO to rhodamine B via Tb(III) cations.

Photoluminescence profiles and fast/slow annealing effects of Eu(III)/Tb(III)-codoped silica phosphor materials.

A silica (SiO2) nanoparticle matrix was codoped with luminescent Eu(III) and Tb(III) ions using a modified Stöber method. The effects of fast and slow thermal annealing on photoluminescence profile imaging were examined. Slow annealing treatment suppressed more quenching sites than fast thermal annealing to further increase the photoluminescence signals. The photoluminescence signals observed between 450 and 720 nm were assigned to the (5)D(0) → (7)F(J) (J = 0,1,2,3,4) of Eu(III) and the (5)D(4) → (7)F(J) (J = 6,5,4,3) transitions of Tb(III). Photoluminescence was largely sensitized by indirect excitation and was much stronger than that generated by direct excitation. The Eu(III) and Tb(III) ions were doped at lower symmetry sites in the silica matrix.

Structural and photophysical properties of HPPCO (4-hydroxy-5-phenyl-6H-pyrido[3,2,1-jk]carbazol-6-one) derivatives.

Proton-substitution effects of 4-hydroxy-5-phenyl-6H-pyrido[3,2,1-jk]carbazol-6-one (HPPCO) on structural and photophysical properties were presented. HPPCO crystallized in the orthorhombic space group Pbca with an intermolecular hydrogen bonding between OH and oxygen atom of the carbonyl. The proton-substituted derivatives, 6-oxo-5-phenyl-6H-pyrido[3,2,1-jk]carbazol-4-yl acetate (OPPCA) and 6-oxo-5-phenyl-6H-pyrido[3,2,1-jk]carbazol-4-yl benzoate (OPPCB), crystallized in the monoclinic P21/c space group. For OPPCA and OPPCB, a weak interaction between carbonyl oxygen atom in the substituted group and carbon atom in the fused ring was responsible for three-dimensional arrangements. In addition, 6-oxo-5-phenyl-6H-pyrido[3,2,1-jk]carbazol-4-yl furan-2-carboxylate (OPPCF), and 6-oxo-5-phenyl-6H-pyrido[3,2,1-jk]carbazol-4-yl naphthoate (OPPCN) were also synthesized. HPPCO and the four derivatives excited by ultraviolet (UV) light produced blue emission. Proton substitution of the OH group significantly increased the radiative transitions and moderately decreased the non-radiative transitions. Consequently the luminescence quantum yields of the derivatives enhanced more than 4.6-fold, no matter what the groups were substituted. Structural and optical properties were further determined using density functional theory (DFT) and ZINDO calculations. The planar structure of the pyridocarbazole-fused ring resulted in π→π(*) electronic transitions within the main frame, with an additional transition from the n(O) of carbonyl to the π(*) of the main frame. The three excited states that arose from these transitions were responsible for the blue luminescence.

Synthesis and characterization of Eu(III)-incorporated silica nanoparticles for application to UV-LED.

A tetrakis(dibenzylmethanido) Eu(III) complex as a ultraviolet (UV) excited phosphor was synthesized, and incorporated with mesoporous silica as core-shell (CS), outer-shell (OS) and intermediate-shell (IS) architectures, using a combination of the self-organization process and the Stöber method. Exciting the Eu(III) complex at UV light produced a strong sensitized red-emission from Eu(III) by energy transfer from the ligand. Phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by casting the powdered complex and the incorporated silica nanoparticles onto a 365-nm InGaN chip, and their optical properties and thermal stability were investigated in terms of the chromaticity index and the intensity decay, respectively. The CS silica nanoparticle casted UV-LED exhibited the best perfomence with strong intensity and excellent thermal stability.

Sensitized luminescence of Eu(III) complexes with Schiff-base and 1,10-phenanthroline: role of Schiff-base as a sensitizer.

The synthesis and characterization of two europium(III) complexes, [Eu(L)(H2O)]Cl and [Eu(L)(phen)(H2O)]Cl (L=N,N'-bis(salicylidene)-3,6-dioxa-1,8-diaminooctanato and phen=1,10-phenanthroline) are reported. Exciting the Eu(III) complexes with near-UV light resulted in sensitized red luminescence by a transfer of energy from the triplet excited states of L to the Eu(III) ion. Introducing phen to the complex increased the quantum yield of the L-sensitized luminescence of [Eu(L)(phen)(H2O)](+) by more than 18 times relative to [Eu(L)(H2O)](+). The optimized structures and the configurational interaction singles (CIS) of the [Eu(L)(phen)(H2O)](+) and [Eu(L)(H2O)](+) molecules were theoretically studied using ab initio Hartree-Fock (HF). The theoretical calculations showed that the first nearly degenerate 1A and 2A excited states, more specifically the π→π(*) transitions of the two phenolate terminals, contributed significantly to the energy transfer process. Although the phen excitation route was forbidden in [Eu(L)(phen)(H2O)](+), the coordination of phen enhanced the absorbing ability of L markedly and caused the energy transfer from the 1A and 2A states to the (5)D1 and (5)D0 states of Eu(III) to predominate over any radiative and nonradiative processes occurring between the excited states and the ground states of the L moiety. Consequently, the quantum yield of the sensitized luminescence was enhanced significantly in [Eu(L)(phen)(H2O)](+).

Synthesis and photophysical properties of an Eu(II)-complex/PS blend: role of Ag nanoparticles in surface-enhanced luminescence.

A novel Eu(II) complex with 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate (EHHEHP or PC88A) was synthesized and blended with polystyrene polymer (PS). Both an independent complex and the Eu(II)/PS blend excited by near-UV light produced blue luminescence, arising from the 5d→ 4f transitions of Eu(II). Time-dependent density functional theory (TD-DFT) calculations on electronic structures of the complex molecule indicated that the absorbing and emitting center was associated with the (2)A(d(z(2))) state under the C(2) crystal field. We also synthesized silver nanoparticles (Ag NPs) with an average particle size of 4.48 nm (σ = 0.91 nm) using EHHEHP as a stabilizer. The effects of Ag NPs as a colloidal suspension and an interfacial layer on the luminescence intensity of the blend were investigated as functions of the concentration of Ag NPs and the thickness of the Ag NP layer, respectively. The critical concentration of the colloidal Ag NPs and the critical thickness of the interfacial Ag NP layer were ∼355 ppm and ∼0.16 µm, respectively. Under critical conditions, the Ag NPs increased the luminescence intensity by 4.4 times as a colloidal suspension in CH(2)Cl(2) and 2.2 times as an interfacial-layer state.

Luminescence properties of 4-hydroxy-5-phenylpyrido[3,2,1-jk]carbazol-6-one: solvatochromism and sensitivity to amine solution.

A detailed photophysical analysis of 4-hydroxy-5-phenylpyrido[3,2,1-jk]carbazol-6-one (HPPCO) is presented. When exposed to UV light, the compound produced deep blue to green luminescence, depending on the solvent. The luminescence peak shifts with the Gutmann donor number (DN) of the solvent and the proton substitution affects luminescence; a correlation between quantum yield and decay time indicated that proton transfer plays a key role in the observed solvatochromism. The ground-state deprotonation of HPPCO was apparently evidenced from the absorption and/or the excitation spectra in the solvents with large DN values. DFT and ZINDO calculations on the structural and optical properties have shown that deprotonation increases the contribution of oxygen atoms to the HOMO, thereby lowering the transition energy from the HOMO to the LUMO. Because the luminescence properties of HPPCO depend on proton transfer, it may be used to detect and quantitate amines in solution. The sensitivity of the luminescence to various amines was ∼10(5) M(-1) and was more effective in ethanol than in methanol.

Optical and conformational studies on benzobisthiazole derivatives.

2,6-Didodecyl-4,8-diphenyl-benzo[1,2-d;4,5-d']bisthiazole (3) and 2,6-didodecyl-4,8-dipyrrole-2-yl-benzo[1,2-d;4,5-d']bisthiazole (5) were synthesized, and their optical properties were investigated in solution and in the solid state. Compounds 3 and 5 were excited with the 325 nm He-Cd laser line to produce blue and green luminescence, respectively. The luminescence of 5 (Phi = 14%) was more efficient than that of 3 (Phi = 5%). Structural and optical properties were further determined with DFT and ZINDO calculations. The planar structure of 5 results in pi --> pi* electronic transitions from the pyrrole moiety to the benzobisthiazole frame, while the twisted geometry of 3 results in luminescence strongly associated with the pi --> pi* transitions within the benzothiazole frame. The effect of solvent on the luminescence properties of 5 is summarized as competition between intra- and intermolecular NH...N hydrogen bonds.

Sensitized near-IR luminescence of Ln(III) complexes with benzothiazole derivatives.

Lanthanide complexes with benzothiazole derivatives (Btz-R, R = OCH(3) and OH) and terpyridine (tpy) ligands were synthesized, and their photophysical properties were precisely investigated. The free Btz-OCH(3) ligand in toluene, excited with UV light, produced the normal emission bands around 410 nm, whereas Btz-OH produced a strong excited-state intramolecular proton transfer (ESIPT) band at 510 nm. The Ln(III) complexes (Ln = Nd, Er, and Yb) exhibited sensitized near-IR luminescence when the Btz-R ligands were excited. The sensitized luminescence quantum yields (Phi(Ln)) of the lanthanide complexes were markedly enhanced by ESIPT: for [Nd(Btz-R)(tpy)] in toluene solution, Phi(Ln) = 0.04% for Btz-OCH(3) and 0.39% for Btz-OH. The sensitized luminescence of the Er(III) complexes (Phi(Ln) = 0.002% for Btz-OCH(3) and 0.009% for Btz-OH) was less efficient than that of the Nd(III) complexes. This difference is due to the smaller energy gap between the emitting and ground levels of the Er(III) ion. The rate constants for the energy transfer from Btz-R to Ln(III) were about approximately 10(9) s(-1), as evaluated by the Förster resonance energy transfer mechanism.

Supramolecular aggregation of mononuclear triorganophosphinegold(I) 2-mercaptobenzamides: solution structures, thermal decomposition, and photoluminescence.

The crystal structures of R3PAu[SC6H4C(=O)NH2-2], R = Et (1), Ph (2), and Cy (3) show linear coordination geometries for gold defined by sulfur and phosphorus atoms. Supramolecular aggregation via {...H-N-C=O}2 synthons lead to dimeric aggregates in each case. In (1) and (2), the aggregates are spherical, but steric effects exerted by cyclohexyl rings in (3) dictate a rodlike form; no Au...Au interactions were noted in the crystal structures. Solvent dependence in their NMR spectra is correlated with intra- and intermolecular hydrogen bonding. The compounds uniformly decompose under controlled conditions to give gold. The complexes excited by UV light produce strong blue-green luminescence. The configuration interaction singles (CIS) post-Hartree-Fock (HF) calculations for the compounds indicate that it is the charge transfer from the sulfur and pi-orbitals of SC6H4C(=O)NH2-2 to gold that produce the emission from gold. The assignment of the observed luminescence is presented in terms of the relaxed excited states of gold, in which the vibronic interactions for three p-orbitals of gold are taken into account.

Photophysical properties and energy transfer pathway of Er(III) complexes with Pt-porphyrin and terpyridine ligands.

The photophysical properties of Er(III) complexes coordinated with platinum[5,10,15-triphenyl-20-(4-carboxyphenyl)-porphyrin] (PtP) and terpyridine (tpy) ligands in organic solution were investigated. The Er(III) complex emitted sensitized near-IR (NIR) luminescence when the PtP ligands were excited under deoxygenated conditions. The quantum yield (PhiLn) of the sensitized luminescence was 0.015%, as evaluated from luminescence lifetime. The photophysical studies and theoretical calculations suggest that the Förster resonance mechanism is very suitable for the energy transfer from PtP to the Er(III) ion and occurred through the first triplet excited state of PtP. The 12.3% energy transfer from the triplet state to the 4F9/2 and 4I9/2 states of Er(III) occurred with a rate distribution of 3.36x10(5) and 6.67x10(4) s(-1), respectively. In addition, the observed triplet quantum yield of the PtP ligand in [Ln(PtP)3(tpy)] proved that the energy transfer from the singlet excited state of the PtP ligand to the Er(III) ion did not take place.

Separating Ag, B, Cd, Dy, Eu, and Sm in a Gd matrix using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester extraction chromatography for ICP-AES analysis.

The separation procedure for Ag, B, Cd, Dy, Eu and Sm as impurities in Gd matrix using ICP-AES technique with an extraction chromatographic column has been developed. The spectral interference of the Gd matrix on the elements was eliminated using a chromatography technique with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) as the mobile phase and XAD-16 resin as the stationary phase. Ag(+), B(4)O(7)(2-), and Cd(2+) were eluted with 0.1M HNO(3), while rare earth ions were not. The best eluent for separating Eu and Sm in the Gd matrix was 0.3M HNO(3). The limit of quantitation for these elements was 0.6-3.0ng mL(-1). The recovery of Ag, B, and Cd was 90-104% using 0.1M HNO(3) as the eluent, while that of Eu, Gd, and Sm ranged from 100 to 102% with 0.3M HNO(3). Dy was recovered quantitatively with 4M HNO(3). The relative standard deviation of the methods for a set of three replicates was between 1.0 and 15.4% for the synthetic and standard Gd solutions. The proposed separation procedure was used to measure Ag, B, Cd, Dy, Eu, and Sm in a standard Gd solution.

Photophysical properties of near-infrared-emitting Ln(III) complexes with 1-(9-Anthryl)-4,4,4-trifluoro-1,3-butandione (Ln = Nd and Er).

We report the synthesis and photophysical properties of Nd(III) and Er(III) complexes with 1-(9-anthryl)-4,4,4-trifluoro-1,3-butandione (9-ATFB). The complexes of [Nd(9-ATFB)4]- and [Er(9-ATFB)4]- produced sensitized near-infrared (NIR) luminescence via the excitation of anthracene. This suggests that the intramolecular energy transfer occurred from the singlet excited state of anthracene to the resonance levels of the metal ions, since the phosphorescence of anthracene is forbidden under normal conditions. The observed quantum yield of the visible luminescence showed that the energy transfer is more efficient for [Nd(9-ATFB)4]- than for [Er(9-ATFB)4]-. The lifetimes of the NIR luminescence of the complexes were in the microsecond range. The quantum yields of the sensitized NIR of the complexes were estimated using the lifetime and the energy-transfer quantum yield.