Jun-Gill Kang

Determination of the structure of EuTETA and the luminescence properties of EuTETA and EuDOTA (TETA=1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetate and DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate)

Abstract The crystal structure and the luminescence of the complex Na[Eu(TETA)]·2H2O·4NaCl (TETA=1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraacetate) have been determined. The space group is P 1 , and the lattice parameters are a=9.283(2) A, b=17.794(3) A, c=19.8087(17) A, α=70.733(11)°, β=83.474(12)°, γ=88.478(18)°, V=3068.6(9) A3, ρ=1.890 g cm−3, and Z=2. The luminescence of Na[EuDOTA·H2O]·3H2O (DOTA=1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) has also been reported. In the TETA macrocycle, the Eu(III) is completely encapsulated via coordination to the four nitrogen atoms and the four carboxylate oxygen atoms of the ligand. The geometry of the eight-coordinate polyhedron is a strongly distorted dodecahedron. The characteristic feature in the geometry is the conformation of the pendant carboxylate arms. The asymmetric unit consists of two independent molecules, differentiated from the helicities of the pendant arms. When the EuTETA and EuDOTA crystals are excited by UV light, they produce very characteristic luminescences responsible for the 5D0→7FJ (J=0, 1, 2, 3, 4) transitions. Unlike the EuDOTA complex, the luminescence structure of the EuTETA complex is significantly affected by the crystalline state. This might be due to the rigidity of the complex. The energy-level schemes of the 7FJ states and detailed assignments for the observed luminescence lines of the EuTETA and EuDOTA complexes have been proposed by phenomenological simulation in the framework of the crystal-field Hamiltonian.

Luminescence and crystal-field parameters of Eu(III) and Tb(III) complexes with nitrilotriacetate

Luminescence spectra of [Eu(NTA)2·H2O]3− and [Tb(NTA)2·H2O]3− crystals measured at 78.8 K are reported. When the crystals are excited by UV light, they produce very characteristic luminescence lines in the 580–720 nm region for [Eu(NTA)2·H2O]3− and in the 450–700 nm region for [Tb(NTA)2·H2O]3−. The energy-level schemes of the 7FJ states and the emitting level for Eu(III) and Tb(III) ions have been proposed by phenomenological simulation in the framework of crystal-field Hamiltonian. The set of refined crystal-field parameters under the C2V site symmetry of the two ions satisfactorily produce good fits between calculated and experimentally observed energy-level structures, associated with the fine splitting of the luminescence lines in the 5D0→7FJ (J=0–4) transitions of the Eu(III) ion in [Eu(NTA)2·H2O]3− and in the 5D4→7FJ (J=6–0) transitions of the Tb(III) ion in [Tb(NTA)2·H2O]3−.

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.

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.

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.

Temperature effect on photoluminescent properties of red light-emitting materials based on Ru(II)-chelated complexes

Abstract A new class of silicon-based copolymers containing Ru(II)-chelated complexes for new red light-emitting materials was developed by well-known Heck reaction between distyrylsilane monomer and the difunctionalized metal-chelated complexes. Ru(II)-chelated copolymers I and II showed one strong band approximately 265–289 nm for ligand units, one strong absorption band approximately 386–392 nm for π-conjugated backbones, and a broad shoulder metal-to-ligand charge transfer band approximately 460–465 nm. Ru(II)-chelated polymers exhibited a negligibly broad band approximately 495–500 nm in the greenish blue region and one/or two strong bands in the red region at room temperature. The photoluminescent (PL) properties of all materials as a function of temperatures were also investigated. With a photoexcitation wavelength of 325 nm at various temperatures, their PL intensity approximately 673–675 nm increased gradually with decreasing temperature, due to the restraint of the thermal relaxation decay.

Ignition delay times of nitromethaneoxygenargon mixtures behind reflected shock

The substituted NO 2 reduced the role of oxygen as the promotor of the detonation and decreased the activation energy, compared with the case of methane. It could be due to one of two factors: the C-N bond energy or the reactivity of the NO 2 radical deriving additional branching chain processes for the detonation reaction

Photophysics of RbCl co-doped with Eu2+ and Eu3+

Abstract Excitation and luminescence spectra of RbCl co-doped with divalent and trivalent europium ions are reported. Spectral dips appearing in the blue emission from Eu 2+ are resulted from the radiative energy transfer from Eu 2+ to Eu 3+ and consequently induces the luminescence from Eu 3+ that is responsible for the 5 D 0 → 7 F J ( J =0, 1, 2, 3, 4) transitions. The induced luminescence has been characterized as a function of temperature and a decay time. In addition, the polarized emission from RbCl doped with only Eu 2+ is also reported.

Spectroscopic studies of Sb3+ color centers in alkali halide single crystals

The emission from KCl: Sb3+ and KI: Sb3+ excited in the A‐absorption band was measured as a function of exciting photon energy and temperature. The A‐band excitation produced two emission bands for KCl: Sb3+ and a single band for KI: Sb3+. The definitive assignment of these bands is presented in terms of the adiabatic potential energy surface (APES), in which the effect of the spin–orbit interaction (SO) on the Jahn–Teller (JT) interaction coupling to the Eg mode is taken into account. The polarization spectrum and the angular dependence of polarization ratio of the A‐band emission were also studied to determine the symmetry axes of the Sb3+ –vacancies complex. The results indicate that the anisotropy is associated with the relaxed excited state (RES) of Sb3+. It is also found that the JT interaction coupling to the T2g mode and the vacancies, situated in the next‐nearest‐neighbor (nnn) and the nearest‐neighbor (nn) positions to the Sb3+ ion, give rise to an additive perturbation.

Polarization of A-band emission from KX:Pb2+ (X = Cl, Br and I)

Abstract The angular dependence of the polarization of the A-band emission from KX: Pb 2+ is measured at low temperature to determine the symmetry axes of the Pb 2+ −v c − dipoles. The results indicate that a Pb 2+ −v c − pair is located along a C 4 crystallographic axis. This implies that the cation vacancy is situated in the next-nearer neighbor (nnn) position to the Pb 2+ impurity. The temperature dependence of the polarization of the A-band emission is also investigated and the results are treated in terms of the same model used to described the decay kinetics.