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Particular features and quenching mechanisms of exciton luminescence of water-soluble nanocomposites that are formed as a result of the interaction of surface charged semiconductor quantum dots (QDs) CdSe/ZnS ( d = 2.8 nm) and cationic porphyrins (HTMPyrP and ZnTMPyrP) have been studied theoretically and experimentally. It has been found that, in CdSe/ZnS⊕Porphyrin conjugates, there occurs long-range inductive resonance electronic excitation energy transfer from surface modified (with thioglycolic or mercaptoundecanoic acid) QDs to porphyrins, which is accompanied by quenching of the exciton luminescence of QDs and an increase in the fluorescence intensity of porphyrin. It has been shown that, when mercaptoundecanoic acid is used as a QD shell, the QD luminescence quenching efficiency by porphyrins follows the Förster-Galanin theory and depends on the overlap integral between the CdSe/ZnS luminescence band and the absorption spectra of free-base porphyrin HTMPyrP and its metal complex ZnTMPyrP. It has been revealed that, as the QDs ↔ Zn-porphyrin intercenter distance decreases from 39.1 (mercaptoundecanoic acid) to 30.1), a considerable QD luminescence quenching is observed; however, the energy transfer efficiency substantially decreases, from 55% in the former case to 23% in the latter one. Based on the spectral-luminescent data and quantum-chemical calculations, it has been found that the chemical change of HTMPyrP in the structure of the complex with CdSe/ZnS QDs passivated by thioglycolic or mercaptoundecanoic acid is caused by the formation of a metal complex ZnTMPyrP. Based on calculations of the redox-potentials, it has been concluded that the low luminescence quantum yield of CdSe/ZnS QDs passivated by residues of mercaptocarboxylic acids S(CH)COO and its dependence on the number of CH groups are related to the possibility of photoinduced electron transfer from the HOMO of passivating molecules to QDs (QD* ⇐ S(CH) nCOO hole transfer). It has been shown that the quenching of the exciton luminescence of QDs in heterogeneous structures CdSe/ZnS(thioglycolic acid)⊕ZnTMPyrP, which is complementary to the energy transfer, can be caused by the photoinduced electron transfer that involves the participation of the LUMO of the ZnTMPyrP molecule (QD* ⇒ ZnTMPyrP). [ABSTRACT FROM AUTHOR]

Unsaturated absorption coefficients in pure carbon dioxide at pressures of 1 and 100 Torr and in CO-N and CO-He binary mixtures at a pressure of 100 Torr have been measured in the temperature range of 296-700 K using a frequency-stabilized tunable CO laser. The collisional self-broadening coefficient, the relative coefficients of collisional broadening caused by N and He buffer gases, and their temperature dependences have been determined for the R22 absorption line of the 100-001 transition in CO molecules. [ABSTRACT FROM AUTHOR]

We present a comprehensive study of spectral photoluminescence (PL), photoconductivity and Hall mobility in undoped, n and p-type modulation-doped quantum wells of Ga1- x In x N y As1- y /GaAs with varying nitrogen concentration. We show that the increasing nitrogen composition red shifts the energy gap and this red shift is accompanied with a reduction of the 2D electron mobility in the quantum wells. True temperature dependence of the band gap, free from errors associated with nitrogen induced exciton trapping effects, is observed because in the modulation doped QW samples PL emission is dominated by band-to-band recombination and the S-shape temperature dependence is eliminated. Excellent fit to semi-experimental Varshni equation is obtained and the temperature dependence of the band gap in the linear regime (d E/d T) is tabulated as a function of nitrogen concentration and the type of dopant. [ABSTRACT FROM AUTHOR]

New absorption bands due to spin-forbidden transitions from the ground state to excited triplet states are found at 295 K in the near-IR absorption spectra of a number of Cu(II) complexes of octaethylporphyrin (OEP) that differ in the nature, number, and position of their side substituents. The frequency distribution, number, and nature of these transitions are analyzed using computer decomposition of complex contours into Gaussian components and additional data from the phosphorescence and phosphorescence excitation spectra (295–77 K). The d-π exchange integrals, determining the energy splitting ΔE = E(2T1) – E(4T1) in the compounds under study, are calculated on the basis of the experimental data obtained. It is shown that, in addition to the formally spin-allowed 2S0→2T1 transition (λmax = 833 nm), the absorption spectrum of the nonplanar CuOETPP molecule at 295 K exhibits the low-intensity spin-forbidden 2S0→4T1 transition (λmax = 937 nm). For this compound at 77 K, phosphorescence from the 4T1 state is observed (λmax = 955 nm), with a quantum yield equal to φPh = 0.0015 and a decay time amounting to τPh = 190 ns. For the CuOEP–Ph(o-NO2) molecule, which contains the electron-acceptor nitro group, direct absorption from the ground state S0 to a charge transfer (CT) state (λmax = 845 nm) is observed at 295 K. The extinction coefficient of this absorption and the energy of the CT state are determined. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

In the present work, results of investigations into the transient absorption of some organic compounds by the method of pulsed flash photolysis are given. Experimental investigations were carried out using an original setup of pulsed flash photolysis with an exciting pulse of XeCl-laser radiation of nanosecond duration and sensing by broadband laser-transient fluorescent radiation of a mixture of organic fluorophors called “white light” excited by the same source in the wavelength range 330–750 nm. The setup registers the short-living (singlet-singlet) and long-living (triplet-triplet) absorptions. The transient absorption spectra of already investigated para-terphenyl, naphthalene, and 1-phenyl-2(2-naphthyl)-ethylene molecules are presented; the spectra of the transient absorption and its nature are in good agreement with the experimental and calculated data published in the literature. We first investigated the transient absorption of LOC1 (S1-Sn at 580 nm and T1-Tn at 500 nm) and phenalemine 512 (S1-Sn at 395 nm). It is demonstrated that the experimentally observed induced absorption of phenalemine 512 and PD 789 is the S1-Sn absorption, which is in good agreement with the results of quantum-chemical calculations. [ABSTRACT FROM AUTHOR]