Additional Absorption Band Research Articles

Nonlinear spectroscopy of CuFe x S y semiconductor nanoparticles

An investigation of the properties of CuFeS2 and CuFe2S3 nanoparticles with a different degree of surface oxidation was carried out. Oxidation leads to the appearance of an additional absorption band with a maximum near 1.1 µm, which is assigned to metal-ligand-type transitions with charge transfer between Cu atoms and their surroundings. Excitation of samples by picosecond laser pulses causes brightening of the additional absorption band and induced absorption, associated with the absorption of their excited states, with two characteristic times of relaxation of nonlinear-optical effects: τ1 = 70 ± 10 and 25 ± 5 psec for CuFeS2 and CuFe2S3 nanoparticles, respectively, and τ2>500 psec for both types of samples. The excitation and relaxation processes are explained on the basis of the proposed scheme of energy levels.

Kinetics of UV laser radiation defects in high performance glasses

High purity fluoride phosphate glasses are attractive candidates as UV transmitting materials. The calculated values for the ultraviolet resonance wavelength are comparable with those of pure silica glass or fluoride single crystal CaF2. The formation of radiation-induced defect centers leads to additional absorption bands in the VUV–UV–vis range. The damage and the healing behavior by lamps and lasers are investigated in dependence on phosphate content and the content of impurities, mainly transition metals. Experiments were carried out using pulsed lasers with a duration of femto- and nanoseconds at a wavelength of 248 nm. The initial slope of the induced absorption shows a nonlinear dependence on the pulse energy density. Resonant and non-resonant two-photon mechanisms were observed. Two-photon-absorption coefficients at 248 nm for samples with different phosphate contents were measured. Models of the kinetics of the radiation-induced defects were developed. The inclusion of energy transfer was necessary to explain the difference in the damage behavior for nanosecond (248 nm, 193 nm) and femtosecond (248 nm) laser pulses.

Laser flash photolysis of sodium persulfate in aqueous solution with additions of dimethylformamide

The method of laser flash photolysis with excitation at 308 nm was used to study the photochemistry of persulfate-ion in aqueous solutions with additions of N, N-dimethylformamide (DMF). The photolysis of S 2O 8 2− in water gives rise to SO 4 − radical anions with a 0.55 quantum yield. The rate constant of SO 4 − recombination was measured (2 k=(2.7±0.2)×10 9 M −1 s −1 at ionic strength μ=0.9 M). In the presence of DMF the additional intermediate absorption band appears with a maximum at 380 nm, belonging to radical CH 2(CH 3)NCHO. Its extinction coefficient was determined ( ε 380=1700±200 M −1 cm −1). The rate constants of reactions SO 4 − +DMF((4.3±0.2)× 10 8 M −1 s −1 ) and CH 2 (CH 3 )NCHO+O 2 ((1.3±0.1)× 10 9 M −1 s − 1 ) were measured. Thus, DMF is a good acceptor of active radicals (e.g., OH radical) which have absorption in the far UV region and which are impossible to detect directly in pulse photochemical experiments.

Nonlinear optical properties of solgel-derived glasses doped with copper selenide nanoparticles

Transient differential absorption spectra of solgel glasses that contain copper selenide nanoparticles (NP’s) have been studied with a picosecond pump–probe technique. Oxidation of copper selenide NP’s results in the appearance of an additional absorption band peaked at ∼1 µm, which can be transiently bleached under laser excitation. Excited-state absorption related to mid-gap surface trap states was observed. The absorption recovery time was found to be ∼300 ps. The intensity-dependent transmission of oxidized copper selenide NP’s in solgel glass at 1.08 µm has been measured. Permanent laser-induced absorption changes in the glasses were studied with nanosecond pulses as a function of laser exposure. Passive Q switching of 1.06-µm Nd3+:Y3Al5O12, 1.34-µm Nd3+:YAlO3, and 1.54-µm Er3+: glass lasers has been realized with the glasses containing copper selenide NP’s used as saturable absorbers. Q-switched pulses with 100-ns (1.06 µm), 90-ns (1.34 µm), and 60-ns (1.54 µm) pulse widths were obtained.

UV Transmission and radiation-induced defects in phosphate and fluoride–phosphate glasses

The relationship between intrinsic and extrinsic ultraviolet (UV) transmission and UV lamp- and laser radiation-induced defects produced in phosphate glasses has been investigated. The composition was varied from simple binary metaphosphate glasses (MPs) to multicomponent ultraphosphate glasses (UPs), which can be melted on a commercial scale, to small amounts of mono- and diphosphates in fluoroaluminate glasses. The effects of the structure-dependent band gap (intrinsic effect) and the Fe 2+/Fe 3+ and P 5+/P 3+/P 0 concentration ratios (extrinsic effect) on the UV absorption, and on the formation and recombination of radiation-induced defects were studied. A correlation has been inferred with the optical basicity of the glass matrix. The kinetics of the photoionization of Fe 2+ to (Fe 2+) + were measured and simulated. This process is single photon, whose rate depends on the phosphate content and increases with increasing phosphate content (increasing basicity). Single and two photon mechanisms were indicated by the excimer laser radiation forming electron and hole defect centers, which were attributed to phosphorus species based on their electron paramagnetic resonance spectra. These defects cause additional absorption bands in the UV-visible region. Differences were detected between phosphate and fluoroaluminate glasses with a phosphate content ⩽20 mol%. The fluoroaluminate glasses have the lowest optical basicity and are stable against UV radiation, but crystallize. The optical basicity increases, the crystallization tendency decreases, and the UV radiation-induced defects increase with increasing phosphate content.

Synthesis and characterization of Cu x S nanoparticles. Nature of the infrared band and charge-carrier dynamics

Abstract CuxS (x = 1,2) nanoparticles have been synthesized utilizing different capping molecules including polyethyleneglycol (PEG), polyvinylpyrrolidone (PVP), casein hydrolysate-enzymatic (CAS), and bovine serum albumin (BSA). The ground-state electronic absorption spectra of the CuxS nanoparticles show three distinct types of CuxS formed: a green type assigned as crystalline CuS, and two brown types assigned as crystalline Cu2S and amorphous Cu2S. The brown types exhibit a steady increase in absorption toward shorter wavelengths starting at around 650 nm, while the green type shows the same steady increase in absorption, but with an additional absorption band in the infrared (IR). The IR band is attributed to an electron-acceptor state lying within the bandgap. ESR measurements of free Cu(II) ions in solution for all samples show the presence of Cu(II) in the brown amorphous samples, but not in the green or brown crystalline samples. Ultrafast dynamics of photoinduced electrons have been measured for all samples using femtosecond-transient absorption/bleach spectroscopy. In all brown Cu2S samples studied, the early time-transient profiles feature a pulse-width-limited (<150 fs) rise followed by a fast decay (1.1 ps) and a slow decay (>80 ps). These decay dynamics were found to be independent of pump power and stabilizing agent. The fast 1.1 ps decay is attributed to charge carrier trapping, while the long decay may be due to either recombination or deep trapping of the charge carriers. The green CuxS samples studied showed interesting power-dependent behavior. At low excitation intensities, the green CuxS samples showed a transient bleach signal, while at high intensities, a transient absorption signal has been observed. The increased transient absorption over bleach at high intensities is attributed to trap-state saturation. A kinetic model has been developed to account for the main features of the electronic relaxation dynamics.

Optical transient bleaching and induced absorption of surface-oxidized CuFeS nanoparticles

Nonlinear optical properties of surface-oxidized CuFexSy (x=1, 2, y=2, 3) nanoparticles incorporated in polymeric film are studied. Surface oxidation of CuFeS2 and CuFe2S3 nanoparticles results in appearance of the additional absorption band with maximum at 1.03 and 1.15 μm, respectively. Bleaching of this additional absorption band in CuFe2S3 particles and the induced absorption in all studied samples after picosecond laser excitation take place. An energy level scheme for CuFeS2 and CuFe2S3 nanoparticles with long-lived trap levels in the band gap is proposed and the origin of additional absorption is discussed. Characteristic times for career relaxation from conduction band to these trap levels are ≈25±5 ps for CuFe2S3 and ≈70±10 ps for CuFeS2 oxidized nanoparticles. The relaxation of electrons from trap levels has a characteristic time of more than 500 ps.

Role of the Type of Impurity in Radiation Influence on Oxide Compounds

Susceptibility to radiation of rare-earth elements and transition metals in Y 3 Al 5 O 12 , YAlO 3 , LiNbO 3 , SrLaGa 3 O 7 , BaLaGa 3 O 7 and SrGdGa 3 O 7 single crystals was investigated. Additional absorption bands after γ-irradiation with doses 10 3 -10 7 Gy and protons with fluencies of 10 13 -10 16 cm -2 were found. A decrease in additional absorption with increasing Pr 3+ , Dy 3+ and Cu 2+ and with decreasing Nd 3+ and Fe 3+ dopant concentration was observed. Dopants like Ce 3+ and Cr 3+ show a relatively complex behavior. This behavior strongly depend on the type of radiation and its dose.

Synthesis and antimicrobial activity of new azomethines synthesized from 4-formyl-1-phenyl-3-aryl(heteryl)pyrazoles

The target l-phenyl-3-aryl(heteryl)pyrazole-4-idenaminocarboxylic acids and their esters (Ilia - lilt) were obtained by nucleophilic addition of the corresponding aminobenzoic acids and their ethyl esters (IIa - lid) to 3-aryl(heteryl)-4-formylpyrazoles (Ia - le). The yields and physicochemical characteristics of the synthesized compounds are presented in Table 1. The proposed structures of all these compounds were confirmed by the results of elemental analyses and IR spectroscopic measurements. Compounds Ilia and IIIn were additionally characterized by 1H NMR spectra. The IR spectra of compounds containing carboxyl groups show absorption bands corresponding to C=O stretching vibrations in the region of 1680-1700cm -I, bands due to C=N vibrations ( 1620 - 1630 cm- I), and bands characteristic of O-H bonds (3390-3450cm -I) and C=C and C=N bonds in aromatic and heterocyclic rings (1540 - 1590 cm- i). The IR spectra of ethyl esters are characterized by a shift of the bands of C=O vibrations to 1740 - 1750 cm- z and by the vanishing of absorption bands belonging to the OH groups. The spectra of compounds Illr- IIIt containing coumaryl substituents show additional absorption bands of the C=O bonds at 1740 cm- I. The IH NMR spectra of compounds Ilia and llIn contain singlet signals from the protons of azomethine groups in the region of 9.34 (Ilia) and 9.25 ppm (llln) and the signals from protons of the HC groups in position 5 of the pyrazole ring at 8.92 (Ilia) and 8.87 ppm (llIb). Protons of the aromatic (heterocyclic) substituents give typical signals in the region of 7.33-8.41 ppm.

Experimental study of NIR absorption due to Nb4+ polarons in pure and Cr- or Ce-doped SBN crystals

A broad absorption band around 0.72 eV, assigned to the absorption of Nb4+ polarons, is observed in strontium barium niobate (SBN) crystals (nominally pure or Cr- or Ce-doped) either under illumination at low temperature or after a previous reduction treatment. The absorption spectra of Nb4+ polarons at low temperature show considerable dichroism, which in reduced SBN crystals exists even far above room temperature. The peak position of the Nb4+ polaron absorption in reduced SBN crystals shifts to higher energies with decreasing temperature. The dependence on light intensity and temperature of the Nb4+ polaron absorption during the build-up process under illumination and the decay process after the illumination is switched off are investigated in detail. Compared with pure SBN, doping with Ce or Cr creates additional absorption bands in the visible (2.6 eV) and red (1.9 eV for Cr doping) spectral regions. Illumination in these absorption bands at low temperature gives rise to strong Nb4+ polaron absorption in the NIR (0.72 eV), giving evidence of the enhanced sensitivity even in the red spectral region for SBN:Cr. The light-induced charge transfer process and formation of Nb4+ polarons in SBN are briefly discussed.

Permanent refractive-index changes in GeO 2 glass slabs induced by irradiation with sub band gap light

Permanent, positive refractive-index changes in pure GeO 2 glass slabs are induced by illumination with light having energy far below that of the fundamental absorption edge. The refractive-index change is tentatively explained by the Kramers–Krönig relationship for an additional absorption band induced in the glass via two competitive photochemical reactions.

Spectroscopic and crystallographic studies of YAG:Pr4+ single crystals

Y3Al5O12 single crystals doped with praseodymium and magnesium ions have been prepared. The reversible color change of these crystals are observed when annealing in oxidizing or reducing atmospheres. The change is ascribed to the formation of Pr4+ in the as-grown crystal, caused by the second dopant, Mg2+. The absorption spectra of YAG:Pr,Mg in the range 200–1100nm, as grown and annealed in air and H2/N2 atmosphere, are presented and discussed. Additional broad absorption bands are observed for the as-grown crystals and those annealed in oxidizing atmosphere. Crystallographic investigations of the original crystal and after annealing in a reducing atmosphere as described above, show no distinct structural differences. A redox mechanism is proposed to explain the color change during annealing.

Excited-state dynamics of poly(para-phenylene)-type ladder polymers at high photoexcitation density

Ultrafast dynamics in methyl-substituted poly(para-phenylene)-type ladder polymer films was studied by femtosecond pump-probe spectroscopy in a wide range of excitation densities, up to values typical for the regime of narrow band emission. The singlet excitons relaxation dynamics, monitored at the stimulated emission peak (2.53 eV), showed an intensity-dependent ultrafast decay component, which occurs on a subpicosecond time scale, ascribed to the onset of an amplified spontaneous emission process. In addition, we attributed the photoinduced absorption bands at 1.48 and 1.9 eV to singlet excitons and polarons, respectively. At high excitation density an additional absorption band becomes evident at 2.63 eV. Based on anisotropy decay kinetics we assigned it to short-lived interchain species.

Ultrafast Excitation Energy Transfer in Multilayered Ultrathin Films of Copper Phthalocyanine and 1,4,5,8-Naphthalenetracarboxylic Dianhydride Revealed by Femtosecond Transient Absorption Spectroscopy

Relaxation dynamics of photoexcited stales in ultrathin multilayered films composed of copper phthalocyanine (CuPc) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), were investigated by femtosecond absorption spectroscopy. Absorption bands due to an electronically excited state and a vibrationally excited state of electronically ground state of CuPc were measured for the excitation at 390 nm and 780 nm. Furthermore, an additional absorption band was observed when excited at 390 nm, which was assigned to an NTCDA excited state. Ultrafast energy transfer from NTCDA to CuPc takes place with the time scale of 1 ps at the interface between NTCDA and CuPc layers.

Time-resolved spectroscopic studies of laser induced processes on terthiophene in inorganic-organic hybrid polymer matrices

The transient spectral behavior of α-terthiophene (3T) in a TiO 2SiO 2 and a SiO 2-inorganic-organic hybrid polymer matrix has been studied after excitation with 12 ps UV pulses at 349 nm. In both materials an excited state absorption from the S 1 state has been observed. Two additional absorption bands observed in the TiO 2SiO 2 hybrid polymer film at 550 and 865 nm were assigned to 3T radical cation transitions. The absence of the radical cation absorptions in the SiO 2-inorganic-organic hybrid polymer film indicates, that titanium is involved in the radical cation formation of 3T. The 3T lifetime of the S 1 state has been determined to be 15 ps in the TiO 2SiO 2 hybrid polymer matrix (TSHP-matrix), 72 ps in the SiO 2 hybrid polymer matrix (SHP-matrix), but 135 ps in dioxane solution. The decay of the radical cations exhibit a fast component (53 ps) and a long living component interpreted as a fast geminate recombination and a trapping process, respectively. The picosecond pump probe experiments show that the radical cation formation starts from higher vibronic levels of the S 1 state and represents an effective competing pathway for the S 1 depletion. The solute-like behavior of 3T molecules incorporated in the hybrid polymer matrices was proved by Raman and steady state absorption measurements.

Nonlinear spectroscopy of oxidised CuInS2 nanocrystals

The pump-and-probe method was used in the picosecond range to study nonlinear absorption in oxidised CuInS2 nanocrystals (of 3 nm radius) embedded in a polymer film. Oxidation gave rise to an additional absorption band with its maximum at 1.03 eV. This band was bleached by excitation with laser pulses of the 1.08 μm wavelength. Fast (∼ 50 ps) capture of carriers by deep trapping states resulted in long-lived (in excess of 300 ps) bleaching and induced absorption. An energy level diagram was proposed for oxidised CuInS2 nanocrystals.

Ir spectroscopy of 2,3-polymethylene-3,4-dihydroquinazolines and their complexes

We have investigated the IR spectra in the region of stretching vibration of N+−H and OH groups of the hydrochlorides of 2,3-trimethylene-3,4-dihydroquinazoline (deoxypeganine, DOP), 2,3-tetramethylene-3,4-dihydroquinazoline (tetrazoline), and 2,3-pentamethylene-3,4-dihydroquinazoline (pentazoline) and peganol and peganine and the corresponding complexes with ZnCl2, CoCl2, and MnCl2. The appearance of two additional absorption bands in the 3100–3300 cm−1 region in the complexes investigated as compared with the corresponding hydrochlorides witnesses the formation of interionic hydrogen bonds between the quinazoline cation and the (MeCl4)2− anion.

Optical transient bleaching/absorption of surface-oxidized CuInS 2 nanocrystals

nanocrystals in a polymer film have been studied with the picosecond pump-probe technique. The oxidized CuInS2 nanocrystals have an additional absorption band with a peak at 1.03 eV, which is bleached under picosecond excitation. Rapid (∼50 ps) trapping into midgap surface states results in long-lived (≫300 ps) bleaching and induced absorption features. A schematical energy-level diagram for oxidized CuInS2 nanocrystals is given based on the experimental results.

Mechanism of One-Electron Oxidation of β-, γ-, and δ-Hydroxyalkyl Sulfides. Catalysis through Intramolecular Proton Transfer and Sulfur−Oxygen Bond Formation

The mechanism of photoinduced electron transfer between sulfur-containing alcohols and the 4-carboxybenzophenone (CB) triplet state in aqueous solution was investigated using laser flash photolysis and steady-state photolysis techniques. Bimolecular rate constants for quenching of the CB triplet state by five hydroxyalkyl sulfides, 2-(methylthio)ethanol (2-MTE), 2,2‘-dihydroxydiethyl sulfide (2,2‘-DHE), 3-(methylthio)propanol (3-MTP), 3,3‘-dihydroxydipropyl sulfide (3,3‘-DHP), and 4-(methylthio)butanol (4-MTB), with varying numbers of OH groups and varying locations with respect to the sulfur atom, were determined to be in the range (3.3−4.8) × 109 M-1 s-1 for neutral solutions. The intermediates identified were the CB ketyl radical anion (CB•-), the CB ketyl radical (CBH•), and intermolecularly (S∴S)-bonded radical cations. An additional absorption band at approximately 400 nm in the transient spectra for some of the hydroxyalkyl sulfides was assigned to the intramolecularly (•S−O)-bonded species (only f...

Passivation, structural modification, and etching of amorphous silicon in hydrogen plasmas

Atomic hydrogen from plasma discharges dissolves in silicon previously amorphized by ion implantation (aSi) in the form of Si–H bonds, giving rise to infrared (IR) absorption at ∼1990 cm−1 and causing partial activation of implanted dopants. Passivation of aSi does not affect the rate at which the material subsequently undergoes solid phase epitaxy. Exposure giving rise to [H]>6 at. % causes the appearance of an additional IR absorption band at ∼2080 cm−1 and coloration of the layer. Despite annealing, the Si–H defects, normal solid phase epitaxy does not occur during subsequent heat treatment. The structural modification by H-plasma exposure coincides with etching of the layer. The observations can be understood in terms of void formation in aSi resulting from the clustering of Si–H.