Changes In Optical Spectra Research Articles

Lectin sensitized anisotropic silver nanoparticles for detection of some bacteria

A method of bacteria detection by sensitized anisotropic silver nanoparticles is presented. Anisotropic silver nanoparticles with two bands of surface plasmon resonance (SPR) are prepared and sensitized with potato lectin. These nanoparticles are able to detect three bacterial species: Escherichia coli, Bacillus subtilis and Staphylococcus aureus. The interaction of these bacteria with such nanoparticles induces drastic changes in optical spectra of nanoparticles that are correlated with bacteria titer. The maximal sensitivity is observed for S. aureus (up to 1.5×104mL−1).

Controlled assembly of gold nanorods using tetrahydrofuran

One dimensional gold nanostructure is one of the most studied colloidal nanostructures due to its unique optical properties and promising applications. Compared with the study of isolated Au nanorods (AuNRs), researches on the controlled assembly of AuNRs in predictable structures and consequent coupling-induced wealthy changes in optical spectra remain challenging at present. In this paper, we present an effective method for assembling AuNRs in side-by-side and end-to-end modes through simply adding water-soluble organic solvents (such as tetrahydrofuran and 3-mercaptopropionic) to the as-prepared AuNRs colloid. These two assembly modes are controlled by the concentration of organic solvent. The longitudinal surface plasma resonance of AuNRs shows great coupling effect for these two assembly modes, blue-shifting during the side-by-side assembling and red-shifting with end-to-end assembling.

Proton tunneling in phase IV of hydrogen and deuterium

Using in situ optical spectroscopy we have investigated the temperature stability of the mixed atomic and molecular phases IV of dense deuterium and hydrogen. Through a series of low-temperature experiments at high pressures, we observe phase III-to-IV transformation, imposing constraints on the P-T phase diagrams. The spectral features of the phase IV-III transition and differences in appearances of the isotopes Raman spectra strongly indicate the presence of proton tunneling in phase IV. No differences between isotopes were observed in absorption spectroscopic studies, resulting in identical values for the band gap. The extrapolation of the combined band gap yields 375 GPa as the minimum transition pressure to the metallic state of hydrogen (deuterium). The minute changes in optical spectra above 275 GPa might suggest the presence of a new solid modification of hydrogen (deuterium), closely related structurally to phase IV.

UV–vis spectroscopic Investigation on γ-irradiated alkali aluminoborate glasses

This research paper reports about the change in optical spectra of alkali aluminoborate glasses under high dose of gamma irradiation. Effect of irradiation on visible spectra finds remarkable applications in optoelectronic materials.Glasses with a host matrix composed of M2O (where M=Na, K), Al2O3, B2O3 were prepared by conventional melt quench technique. Gamma irradiation was performed at a dose-rate of 573Gy/h to a total dose of 50kGy. Samples were characterised before and immediately after irradiation by UV–vis transmission spectra in the range of 200–800nm. The induced absorption coefficient and loss of transmission due to irradiation were attributed to the nature of alkali metals as well as the host matrix.

Spectroscopic investigation on phase transitions for Ge2Sb2Te5 in a wide photon energy and high temperature region

We investigated the electronic properties of phase-change material Ge2Sb2Te5 (GST) films using spectroscopic ellipsometry in a wide photon energy and high temperature region. Apart from the charge carrier response, the totality of optical conductivity spectra for three phases of GST films, i.e., amorphous (AM), face-centered-cubic (FCC), and hexagonal (HEX), is quite similar, composed of two interband transitions in visible and UV regions. From optical analysis in a wide photon energy region up to 8.7eV, we found that the intensity as well as the position of the interband transition in the visible region changes significantly as the phase of GST films turns from the amorphous to the crystalline phase, which is consistent with previous theoretical studies. In high temperature measurements above room temperature for the three phases of GST films, we found that the change of optical response for the AM phase of GST film occurs abruptly through two successive phase transitions near 150°C and 270°C, while the optical spectra of the FCC phase shows a change only near 270°C. In contrast to the two above-mentioned cases, a slight change in optical spectra is observed for the HEX phase with the increasing temperature. From the measured optical spectra, we derived the temperature dependence of optical bandgap for the three phases, which are closely correlated to the change of the transport property for the GST films.

A new insight into the mechanism of influence of different inorganic salts on optical properties of water‐soluble cationic conjugated polymers

AbstractThe water‐soluble conjugated polyelectrolyte poly{2,5‐bis[3‐(N,N,N‐triethylammoniumbromide)‐1‐oxapropyl]‐1,4‐phenylenevinylene} (P2) was synthesized and the influences of different inorganic salts on the optical properties of the polyelectrolyte were studied. New absorption and emission peaks at longer wavelength can be observed in the case of P2 with addition of different concentrations of Cl− or NO3−, whereas addition of I− or ClO4− only induces a red shift. Interestingly, addition of SO42− or F− does not result in considerable changes in optical spectra. Through UV‐visible spectrometry, photoluminescence, 1H NMR and cyclic voltammetry, we showed that the nature of the inorganic salts brings these different changes. The special structure of the $\prod{_{4}}^{6}$ bond of NO3− and the large electronegativity of chlorine lead to an electron transfer between the conjugated polymer and the negative ions. The large radius of I− and the weak electron withdrawing ability of ClO4− only bring a red shift of optical spectra. In addition, SO42− and F− do not affect the spectra significantly, except that the fluorescence intensity falls slightly indicating that P2 is not sensitive to these ions. Copyright © 2011 Society of Chemical Industry

Ultra-high sensitivity optical stress sensor based on double-layered photonic crystal microcavity

In this report, we present the design principles to achieve a highly sensitive optical stress sensor. The structure we use is a double-layered (DL) photonic molecule with optical bonding and anti-bonding states based on whispering-gallery mode in photonic crystal microcavity. By applying finite-difference time-domain and finite-element methods, we simulate the change of optical properties (including wavelength and quality (Q) factor) of bonding mode caused by the DL structural variation due to the applied stress in two DL geometries. In the end, we summarize an optical stress sensor design with high Q factor, large structural response due to the applied stress, and large optical spectrum change due to the DL structural variation. The minimum detectable stress variation is estimated to be as small as 0.95 nN.

All-Optical Chromatic Dispersion Monitoring for Phase-Modulated Signals Utilizing Cross-Phase Modulation in a Highly Nonlinear Fiber

We propose and experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique for phase-modulated signals utilizing the cross-phase-modulation effect between the input signal and the inserted continuous-wave probe. The probe's optical spectrum changes with the accumulated CD on the input signal, indicating that the optical power variations can be measured for monitoring. The experimental results show that this technique can monitor up to 120 ps/nm of CD for a 40-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) transmission system, with the maximum measured optical power increment of 16.5 dB. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s RZ differential quadrature phase-shift keying and 80-Gb/s polarization-multiplexed RZ-DPSK, is also investigated via simulation.

Comparing zinc and manganese porphyrin LB films as amine vapour sensing materials

Both 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-porphinato manganese (III) (MnEHO) and 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-porphinato zinc (II) (ZnEHO) solid-state films have been prepared using the LB technique. Calix[8]arene has been mixed with the ZnEHO and MnEHO to enhance the quality of the porphyrin films, their response to amine gases and also increase film lifetime. UV–vis spectroscopy has been used to study the response of these films to amine vapour. Both ZnEHO and MnEHO show spectral changes under exposure to each of the primary, secondary and tertiary amine gases. Interestingly, the ZnEHO displays a spectral red-shift, with largest spectral changes occurring at 421 nm, whereas the MnEHO displays a blue-shift, with largest optical changes occurring at 467 nm. ZnEHO shows a significantly larger optical spectrum change once amine vapours are introduced to the samples compared with the MnEHO; therefore, ZnEHO is more suitable for amine sensing in a sensing device.

Optical response of ferromagneticYTiO3studied by spectral ellipsometry

We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric $\mathrm{Y}\mathrm{Ti}{\mathrm{O}}_{3}$ single crystal with ferromagnetic Curie temperature ${T}_{C}=30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The optical response exhibits a weak but noticeable anisotropy. Using a classical dispersion analysis, we identify three low-energy optical bands at 2.0, 2.9, and $3.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Although the optical conductivity spectra are only weakly temperature dependent below $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, we are able to distinguish high- and low-temperature regimes with a distinct crossover point around $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The low-temperature regime in the optical response coincides with the temperature range in which significant deviations from a Curie-Weiss mean-field behavior are observed in the magnetization. Using an analysis based on a simple superexchange model, the spectral weight rearrangement can be attributed to intersite ${d}_{i}^{1}{d}_{j}^{1}\ensuremath{\rightarrow}{d}_{i}^{2}{d}_{j}^{0}$ optical transitions. In particular, Kramers-Kronig consistent changes in optical spectra around $2.9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ can be associated with the high-spin-state $(^{3}T_{1})$ optical transition. This indicates that other mechanisms, such as weakly dipole-allowed $p\text{\ensuremath{-}}d$ transitions and/or exciton-polaron excitations, can contribute significantly to the optical band at $2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The recorded optical spectral weight gain of the $2.9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ optical band is significantly suppressed and anisotropic, which we associate with complex spin-orbit-lattice phenomena near the ferromagnetic ordering temperature in $\mathrm{Y}\mathrm{Ti}{\mathrm{O}}_{3}$.

Optical absorption spectra of ferropericlase to 84 GPa

Optical and near infrared absorption spectra of ferropericlase Mg 0.88 Fe 0.12 O have been measured to 84 GPa. Under ambient conditions, the spectrum shows two crystal field bands of high-spin Fe 2+ at 8922 and 12 533 cm −1 , which shift to higher frequencies with increasing pressure (dν/d P = 50.7 and 85.5 cm −1 /GPa). Simultaneously, the intensity of the high-frequency band continuously decreases until it vanishes around 40 GPa, suggesting a quenching of the Jahn-Teller effect. Between 51 and 60 GPa, the absorption spectrum changes drastically. Two new bands appear at 60 GPa at 9728 and 14 592 cm −1 with frequency shifts at higher pressures of dν/d P = 23.8 and 21.0 cm −1 /GPa, respectively. If the change in optical spectra between 51 and 60 GPa were interpreted as being due to spin-pairing, the crystal field parameters of low-spin Fe 2+ at 60 GPa would be Δ = 10 546 cm −1 and B = 377 cm −1 . This would imply that the main cause of spin-pairing is not the increase in crystal field splitting Δ, but the stronger covalency of the Fe-O bond as seen in the reduction of the Racah parameter B. Even at 84 GPa, ferropericlase is by no means opaque. In particular, the inferred spin-pairing transition between 51 and 60 GPa reduces radiative thermal conductivity only by about 15%. Spin-pairing in ferropericlase is therefore unlikely to have major consequences for the temperature distribution or the mode of convection in the lower mantle. The absorption edge of the high-pressure phase appears to be deeper in the UV than for the low-pressure phase, which could imply a reduced electrical (polaron) conductivity.

Pressure dependence of the phase separation in deuterated [formula omitted] at the Mott boundary

The pressure dependence of the optical reflectivity spectrum [ R ( ω ) ] of deuterated κ - ( BEDT - TTF ) 2 Cu [ N ( CN ) 2 ] Br ( d 44 ) at T = 4.5 K was determined. At the ambient pressure, d 44 under fast cooling conditions forms an antiferromagnetic insulator (AFI) phase, as confirmed by the wavenumber of the ν 3 ( a g ) vibration mode. At the pressures in the range of several MPa, the optical spectrum changes to that of a metal that matches a non-deuterated material consisting of AFI and PM (paramagnetic metallic) spectra. This indicates that the phase separation between the AFI and PM phases appears at intermediate pressures. The phase size of the separated phase is smaller than the instrumental spatial resolution of 50 μ m , based on the inability of our methods to record it.

Thermal stability of radiation-induced optical centers in non-stoichiometric spinel crystals

The successive anneals of the neutron-irradiated non-stoichiometric spinel crystals MgO·2.2Al2O3 leads to incremental change of optical spectra that demonstrates two main bands whose intensity and spectral position depends on annealing temperature. While temperature increases from 450 to 750K, one of the bands shifts from photon energy of 4.2–5.1eV. Another one shifts in the opposite direction from 6.4–5.6eV. This effect can be attributed to coagulation of radiation induced defects near cation vacancies and change of the energy levels and transitions in F+- and F-centers in neutron-irradiated crystals. The final position of these two bands 5.1 and 5.6eV corresponds to transitions in F+- and F-centers in non-stoichiometric spinel, respectively. The investigation of optical centers induced at subsequent UV-illumination of neutron-irradiated crystals annealed to temperature of 750K, and comparison with as-grown crystals, shows the existence of residual concentration mainly of the antisite defects and partially of the anionic vacancies in the neutron irradiated and annealed crystals. The existence of two temperature stages where optical centers at antisite defects are effectively destroyed may indicate the presence of spatially correlated and isolated antisite defects in irradiated spinel.

Electronic, optical spectra and the distribution of Mn impurities in GaN and group-IV semiconductors

By use of the first-principles density-functional approach, pair impurity configurations, magnetic and optical properties of Mn-doped GaN, Ge and Si were calculated. From the total energies calculated for various possible distributions, substitutional Mn atoms in GaN were found to prefer the dimer configuration with the shortest Mn–Mn distances, while in Ge:Mn and Si:Mn the uniform distribution of Mn atoms is more stable. The most remarkable changes in optical spectra occur in the infrared region due to the optical interband transitions between impurity-induced states.

Terahertz-Induced Changes of Optical Spectra in GaAs QuantumWells

We have theoretically investigated optical absorption spectra inGaAs quantum well (QW) driven by both a strong terahertz (THz)field and a near-infrared field within the theory of densitymatrix. In presence of a strong THz field, the optical transitionsin the QW subbands are altered by the THz field. The alteration has adirect impact on the optical absorption and results in the Autler–Townessplitting and the sidebands generation, which is in agreement with theexperiments.

Photo-induced interband absorption in group-III nitride quantum wells

We solve self-consistently Schrödinger and Poisson equations for GaN/AlGaN quantum wells, to analyze the change of optical spectra under high optical excitation. Electric fields of ∼1 MV/ cm or higher are present along the growth axis of such quantum wells. The induced separation of electron and hole wave functions reduces the oscillator strength of the ground-state optical transition, whereas those involving excited states give a much larger absorption. In presence of large electron–hole pair densities, we show that the optical density can be either reduced or enhanced, depending on the spectral region involved.

Electronic properties of quantum-dot molecules

We investigate the electronic structure of several double quantum dot systems: (i) hetero-dot artificial molecules built from two CdS chemically synthesized nanocrystals and (ii) two vertically stacked pyramidal self-organized InAs/GaAs quantum dots. The calculations are performed using the empirical tight-binding approach. The results of calculations show significant coupling between the nanocrystals that form a quantum-dot molecule. When two quantum dots are close enough, the strong coupling can split and reorder energy levels, change state symmetries and make substantial changes in optical spectra. Formation of double-dot states having bonding and antibonding character by analogy to diatomic molecules is shown.

Studies on the optical and electrical properties of poly(4-vinyl pyridine)/CuPc composite doped with iodine

Optical and electrical properties of Cu–phthalocyanine (CuPc) microparticle dispersed poly(4-vinyl pyridine) (P4VP) films have been studied. Optical micrographs of these composites reveal homogeneous dispersion of CuPc in P4VP. There is a change in optical spectrum due to weak bonding of phthalimide units with basic pyridine groups. The conductivity increases by 3–4 orders of magnitude depending on the percentage of CuPc. I/ V study shows that there is non-Ohmic dependence of current at low field but turns to Ohmic at high field region. On increasing temperature, thermally generated carriers cause Ohmic conduction even at low field. On further doping with I 2, the conductivity is found to increase by 5–6 orders of magnitude. For I 2 doped composite, UV-Vis spectrum shows substantial decrease in the intensity of broad peak (600–700 nm) of CuPc revealing complete absorption of Pc moieties by I 2. From I/ V characteristics, it is found that the conduction is Ohmic in the low-field region and space charge limited current (SCLC) type at high field and high temperature. Thermal activation of large number of carriers gives large increase in current conduction.

Optical Spectroscopy of Perovskite-Type Manganites

Review is given on late optical studies on colossal magnetoresistance (CMR) manganites with perovskite or related structures. In La1−xSr x MnO3 which undergoes a ferromagnetic transition, optical conductivity spectrum σ(ω) shows a change from a gap-like feature to metallic but highly diffussive one with increasing spin-polarization. Such a remarkable spectral weight transfer is also observed in a layered manganite, La2−2xSr1+2xMn2O7 (x = 0.4), with a mid-infrared peak structure due to inter-orbital \((d_{x^2 - y^2 } \to d_{3z^2 - r^2 } )\) transition. In Pr1−xCa x MnO3 (x = 0.4) which undergoes the charge ordering phase transition, σ(ω) shows an anisotropic feature reflecting charge/orbital ordering pattern at 10 K. The charge-ordered state is transformed into a ferromagnetic metallic state by a magnetic field of 6.5 T at 30 K, which is manifested in a huge change of optical spectra over a wide photon-energy region (0.05 eV–3 eV).

Evolution of the optical properties of single-crystal La1−x SrxMnO3

An ellipsometric method is used to study the dispersion of the real ɛ 1(ω) and imaginary ɛ 2(ω) parts of the complex dielectric permittivity of single-crystal La1−x SrxMnO3 (x=0.1, 0.2, and 0.3) for energies from 100 meV to 5 eV at room temperature. It is found that, when lanthanum is replaced by strontium, the optical spectrum changes fundamentally. A shift in the main features of the spectrum of initial LaMnO3 at 1.9 and 4.7 eV to lower energies takes place, as well as a partial redistribution of the optical-conductivity spectral weight in the band gap region E<1.7 eV. For compositions with x=0.2 and 0.3, a fine structure of the interband absorption is observed against a background of non-Drude optical conductivity at low energies.