Steady-state Luminescence Measurements Research Articles

Luminescence of Agrellite Specimen from the Kipawa River Locality

Using steady-state luminescence measurements, the luminescence spectra of Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Dy3+, Er3+ and Yb3+ for the agrellite sample from the Kipawa River region have been measured. The emission spectra of Eu3+ and Dy3+ next to those of Sm3+ and Pr3+ have been measured for characteristic excitation conditions. The most efficient luminescence activator in the studied sample was Ce3+. This ion was also a sensitizer of Pr3+, Sm3+, Eu3+, and Dy3+ luminescence.

Radiation-induced optical change of ion-irradiated CdSeS/ZnS core-shell quantum dots embedded in polyvinyl alcohol

Semiconductor quantum dots (QDs) are receiving increasing interest for the production of scintillator detectors and dosimeters. For this reason, the investigation of the effects of ionizing radiation on the optical properties of QDs has become of great importance. In this paper, we present the optical characterization of colloidal CdSeS/ZnS core-shell quantum dots (QDs) embedded in a polyvinyl alcohol (PVA) matrix and irradiated with 2 MeV H+ and He+ ions at different fluences. With steady-state luminescence measurements, we investigate the ion irradiation effects on the luminescence spectrum of the irradiated samples. With time-resolved luminescence measurements, acquired with a Time Correlated Single Photon Counting (TCSPC) system, we evaluate the radiation-induced change in the QD charge carrier dynamics. Luminescence spectra show the appearance of new features related to damage of the PVA host. Time-resolved measurements highlight a shortening of the QD luminescence time constants as the ion fluence increases.

Photophysical Characterization of the Interactions among Tris(2,2′-bipyridyl)ruthenium(II) Complexes Ion-Exchanged within Zirconium Phosphate

We studied the structures, luminescence, and self-quenching properties of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) two-dimensional arrangements within the layers of zirconium phosphate (ZrP). The intercalation of Ru(bpy)(3)(2+) was accomplished using a hydrated form of zirconium phosphate ZrP. Varying the Ru(bpy)(3)(2+)/ZrP intercalation ratio, different Ru(bpy)(3)(2+)-exchanged ZrP loading levels were achieved. The ion exchange of Ru(bpy)(3)(2+) within ZrP produces a red shift in the metal-to-ligand charge-transfer (MLCT) absorption band of the complex from 452 nm in aqueous solution to 460 nm in ZrP. Steady state luminescence spectra of the Ru(bpy)(3)(2+)-exchanged ZrP materials show an increase in the luminescence intensity with an increase in the Ru(bpy)(3)(2+) loading level until about 0.77 M, where subsequent increases in the loading level produce a decrease in the luminescence (self-quenching region). Time-resolved luminescence measurements are consistent with the steady state luminescence measurements. Analysis of the time domain luminescence measurements in loadings higher than 0.77 M leads to the determination of a collisional quenching rate constant of (1.67 +/- 0.05) x 10(6) M(-1) s(-1). Stern-Volmer analysis of the luminescence quantum yield of Ru(bpy)(3)(2+)-exchanged ZrP materials indicates that static quenching is also involved in the Ru(bpy)(3)(2+) self-quenching mechanism. The quantum yield data behavior might be explained by a model that takes into account collisional quenching and the quasi-static Perrin mechanism. The calculation yields a quenching sphere of action of 14.8 A, which is slightly larger than the collisional radii of two Ru(bpy)(3)(2+) ions (12.2 A), as predicted by the model.

Upconversion in Nd3+-doped glasses: Microscopic theory and spectroscopic measurements

In this work, we report a systematic investigation of upconversion losses and their effects on fluorescence quantum efficiency and fractional thermal loading in Nd3+-doped fluoride glasses. The energy transfer upconversion (γup) parameter, which describes upconversion losses, was experimentally determined using different methods: thermal lens (TL) technique and steady state luminescence (SSL) measurements. Additionally, the upconversion parameter was also obtained from energy transfer models and excited state absorption measurements. The results reveal that the microscopic treatment provided by the energy transfer models is similar to the macroscopic ones achieved from the TL and SSL measurements because similar γup parameters were obtained. Besides, the achieved results also point out the migration-assisted energy transfer according to diffusion-limited regime rather than hopping regime as responsible for the upconversion losses in Nd-doped glasses.

Single- and Two-Photon Properties of a Dye-Derivatized Roussin's Red Salt Ester (Fe2(μ-RS)2(NO)4) with a Large TPA Cross Section

The synthesis, characterization, photochemistry, and two-photon photophysical properties of a new dye-derivatized iron sulfur nitrosyl cluster Fe2(mu-RS)2(NO)4 (AFX-RSE, RS = 2-thioethyl ester of N-phenyl-N-(3-(2-ethoxy)phenyl)-7-(benzothiazol-2-yl)-9,9-diethyl-fluoren-2-yl-amine) were investigated. Under continuous photolysis, AFX-RSE decomposes with modest quantum yields (Phi(diss) = (4.9 +/- 0.9) x 10(-3) at lambda(irr) = 436 nm) as measured from the loss of the nitrosyl bands in the IR absorbance spectrum. Nitric oxide (NO) was qualitatively demonstrated to be photochemically produced via single-photon excitation through the use of an NO-specific electrode. Steady-state luminescence measurements have shown that AFX-RSE fluorescence is about 88% quenched relative to the model compound AF-tosyl. This is attributed to a relatively efficient energy transfer from the excited states of the antenna chromophores to the dinuclear metal center, with the subsequent production of NO. In addition, the two-photon absorption (TPA) cross sections (delta) were measured for the AF-chromophores via the two-photon excitation (TPE) photoluminescence technique using a femtosecond excitation source. The TPA cross section of AFX-RSE was found with this technique to be delta = 246 +/- 8 GM (1 GM = 10(-50) cm4 s photon(-1) molecule(-1)).

Luminescent Ruthenium(II)− and Rhenium(I)−Diimine Wires Bind Nitric Oxide Synthase

Ru(II)- and Re(I)-diimine wires bind to the oxygenase domain of inducible nitric oxide synthase (iNOSoxy). In the ruthenium wires, [Ru(L)2L']2+, L' is a perfluorinated biphenyl bridge connecting 4,4'-dimethylbipyridine to a bulky hydrophobic group (adamantane, 1), a heme ligand (imidazole, 2), or F (3). 2 binds in the active site of the murine iNOSoxy truncation mutants Delta65 and Delta114, as demonstrated by a shift in the heme Soret from 422 to 426 nm. 1 and 3 also bind Delta65 and Delta114, as evidenced by biphasic luminescence decay kinetics. However, the heme absorption spectrum is not altered in the presence of 1 or 3, and Ru-wire binding is not affected by the presence of tetrahydrobiopterin or arginine. These data suggest that 1 and 3 may instead bind to the distal side of the enzyme at the hydrophobic surface patch thought to interact with the NOS reductase module. Complexes with properties similar to those of the Ru-diimine wires may provide an effective means of NOS inhibition by preventing electron transfer from the reductase module to the oxygenase domain. Rhenium-diimine wires, [Re(CO)3L1L1']+, where L1 is 4,7-dimethylphenanthroline and L1' is a perfluorinated biphenyl bridge connecting a rhenium-ligated imidazole to a distal imidazole (F8bp-im) (4) or F (F9bp) (5), also form complexes with Delta114. Binding of 4 shifts the Delta114 heme Soret to 426 nm, demonstrating that the terminal imidazole ligates the heme iron. Steady-state luminescence measurements establish that the 4:Delta114 dissociation constant is 100 +/- 80 nM. Re-wire 5 binds Delta114 with a K(d) of 5 +/- 2 microM, causing partial displacement of water from the heme iron. Our finding that both 4 and 5 bind in the NOS active site suggests novel designs for NOS inhibitors. Importantly, we have demonstrated the power of time-resolved FET measurements in the characterization of small molecule:protein interactions that otherwise would be difficult to observe.

Chiral recognition phenomena probed by steady-state luminescence measurements: Stern-Volmer analysis of chiral discriminatory behavior.

The chiral recognition phenomenon observed in enantioselective excited-state energy transfer processes currently requires the use of chiroptical spectroscopic techniques to probe the magnitude and sense of the discriminatory interactions. The use of chiroptical spectroscopic techniques limits the study of chiral recognition to those molecular species with strong absorption or emission dissymmetry factors. This study presents the theoretical and experimental methodology to determine the magnitude of chiral discriminatory interactions with unpolarized, steady-state luminescence measurements. Based on bimolecular luminescence quenching kinetics for a system containing chiral molecules, the Stern-Volmer equation is derived and contains a chiral discriminatory term for a system containing a chiral but racemic luminophore and an enantiomerically resolved quencher species. The utility of this methodology is confirmed by examining the enantioselective excited-state quenching between several Ln(dpa)(3)(3-) complexes (where Ln = Eu(3+), Tb(3+), or Dy(3+) and dpa = pyridine-2,6-dicarboxylate) acting as the energy donor and either racemic or enantiomerically resolved [Co(dach)(3)](3+) (where dach = trans-1R,2R (or 1S,2S)-diaminocyclohexane) acting as the energy acceptor in an aqueous solution. The results of this study confirm the utility of unpolarized, steady-state luminescence measurements as a probe of chiral discriminatory behavior.

The luminescence of nanocrystalline ZnO particles: the mechanism of the ultraviolet and visible emission

Results of steady-state luminescence measurements performed on suspensions of nanocrystalline ZnO particles of different sizes are presented. In all cases two emission bands are observed. One is an exciton emission band in the UV and the second an intense and broad emission band in the visible, shifted by approximately 1.5 eV with respect to the absorption onset. As the size of the particles increases, the intensity of the visible emission decreases, while that of the exciton emission increases. In accordance with previous results, a model is presented in which the visible emission is assigned to the radiative recombination of an electron from a level close to the conduction band edge and a deeply trapped hole in the bulk (V ⋅⋅ O) of the ZnO particle. The size dependence of the intensity ratio of the visible to exciton luminescence and the kinetics are explained by a model in which the photogenerated hole is transferred from the valence band to a V ⋅ O level in the bulk of the particle in a two-step process. The first step of this process is an efficient surface-trapping, probably at an O 2− site.

Laser-induced photoelectrochemistry: time-resolved luminescence studies of cds electrodes

The luminescence lifetime of a tellurium-doped CdS electrode in alkaline sulfide electrolyte has been determined. The decay is not a single exponential; the nominal lifetime varies from ⩽ 10 to⩾ 250 ns as a function of laser power, wavelength, and electrode potential. The results are discussed relative to recent steady-state luminescence measurements and time-resolved coulostatic photoelectrochemicai measurements.