Time-dependent micro-Raman scattering studies of polyvinyl alcohol and silver nitrate thin films

In-situ monitoring of silver nanoparticle formation was studied in thin films of polyvinyl alcohol and silver nitrate. We proposed the observation of surface-enhanced Raman spectroscopy (SERS) as a novel and simple technique to record the growth of silver nanoparticles in polyvinyl alcohol thin films. Observed enhancement in the Raman bands of polyvinyl alcohol is explained through the localized surface plasmon resonance of silver nanoparticles. Influence of temperature generated by silver nanoparticles on the formation of nanoparticles is also discussed.     

Effect of post-thermal annealing on the structural and optical properties of ZnO thin films prepared from a polymer precursor

ZnO thin films were synthesised by a new method which uses polyvinyl alcohol (PVA) as the polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural parameters, like grain size, lattice constants, optical band gap, and Urbach energy, depend on the annealing temperature and time. All the films possess tensile strain, which relaxes as the annealing temperature and time increase. The photoluminescence (PL) spectra contain only ultraviolet (UV) peaks at low temperature, but as the annealing temperature and time increase, we observe peaks at the blue and green regions with a variation in the intensities of these peaks with annealing temperature and time.     

Effect of post thermal annealing on the structural and optical properties of ZnO thin films prepared from polymer precursor

ZnO thin films were synthesised by a new method which uses polyvinyl alcohol (PVA) as polymer precursor. The films are annealed at different temperatures and for different annealing times. The structural parameters, like grain size, lattice constants, optical band gap, and Urbach energy, depend on the annealing temperature and annealing time. All the films possess tensile strain which relaxes as the annealing temperature and the annealing time increases. The photoluminescence (PL) spectra contain only ultraviolet (UV) peaks at low temperature, but as the annealing temperature and time increase we observe peaks at blue and green regions with variation of the intensities of these peaks with annealing temperature and annealing time.     

Photoluminescence properties of Mn-doped II–VI semiconductor nanocrystals

Our recent photoluminescence studies on ZnS:Mn²⁺- and CdS:Mn²⁺-nanocrystals dispersed in polyvinyl alcohol polymer films are reviewed. Both nanocrystal samples show Mn²⁺ 3d intrashell luminescence with high quantum efficiencies of about 20% at room temperature under the interband excitation. Noticeable characteristics of our nanocrystal samples are that the luminescence involving some trap state is much weaker than the Mn²⁺ luminescence, unlike other reports, and that thermal quenching of the Mn²⁺ luminescence is remarkably weak, compared with the corresponding bulky crystal powder. These two characteristics lead to the above high quantum efficiencies of the Mn²⁺ luminescence at room temperature. In addition, we examine the dominant excitation mechanism of Mn²⁺ in the nanocrystals under the interband excitation and the validity of the sp–d mixing model proposed previously to explain the high luminescence quantum efficiency.     

Time-resolved streak camera system with solid state laser and optical parametric generator in different spectroscopic applications

Apparatus to study time-evolution of emission spectra over very wide time and spectral range is described. Excitation part of the equipment consists of solid state Nd:YAG laser and optical parametric generator. The heart of the detection system consists of spectrograph and streak camera. The significance of optics and electronics built in the system for proper, fast and convenient measurements is underlined. The results of donor-acceptor energy transfer in a rigid polyvinyl alcohol matrix serve here as an example of application our equipment to study complex systems.     

Change in optical path length of saturable absorbing dye-doped polymer films under laser irradiation

The cause of the change in the optical path lengthΔ(nd) of the saturable absorbing dye-doped polymer films under laser irradiation is investigated using polyvinyl alcohol and gelatin films doped with erythrosin B. The temperature rise of the dye-doped films, the changes in optical path length, film thickness, the refractive index and the optical density of the dye-doped films are measured under laser irradiation. The thermal expansion due to the temperature rise of the dye-doped films caused by the irradiation has greater effect on theΔ(nd) than the fading of dye molecules due to the irradiation of laser beams.     

Thermally stimulated transformation of the structure of cobalt complexes in polyvinyl alcohol-cobalt(II) chloride systems

We present the kinetic and temperature dependences of the optical absorption of thermochromic films of polyvinyl alcohol with added CoCl₂. Based on the data obtained, we have analyzed the possibility that tetrahedral cobalt complexes are formed from octahedral complexes. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 826–829, November–December, 2007.     

Z-scan determination of third-order nonlinear optical nonlinearity of three azobenzenes doped polymer films

The third-order nonlinear response of methyl red (MR), methyl orange (MO) and p-dimethylamino benzene arsenic acid (PDBAA) doped polyvinyl alcohol (PVA) films are studied by using the Z-scan technique under 532 nm and 1064 nm excitations. The larger third-order nonlinear refractive index of PDBAA doped PVA film is discussed in terms of fall of the energy level in excited state for the effect of heavy-atom arsenic. At the end, the second hyperpolarizabilities of the films are estimated and the figures of merit are evaluated for their value of applications in ultra-fast all-optical devices.     

Effect of PVA addition on formation of spray-deposited Sm<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> thin films on CeO<Subscript>2</Subscript> substrates

Nano-crystalline films of Sm_0.5Sr_0.5CoO₃ (SSC) have been formed on CeO₂ substrates by spraying stoichiometric aqueous solution containing Sm, Sr, and Co ions. Effect of polyvinyl alcohol (PVA) addition as a complexing agent in spray solution on stoichiometry, crystallite size, morphology, and transport properties of film are studied. The results showed that the SSC cathode had maximum crystallite size for 40% PVA addition. Electrical performance of film decreases with decrease in the particle size, while the electronic to ionic predominance transition temperature decreases with decreasing particle size. These films are studied for their potential application as a cathodic material in developing intermediate temperature solid oxide fuel cells.     

An oscillator model for the molecules of indole derivatives

Polarization and dichroism measurements are reported for the fluorescence and phosphorescence from isotropic and anisotropic films of polyvinyl alcohol containing indole derivatives; the oscillator model is discussed.     

氢化非晶碳薄膜的光致发光线型及其激发能量依赖关系

本文报道了氢化非晶碳薄膜在2.9-4.5eV光激发下的发光谱。它的光致发光谱是无结构的不对称宽带,半宽度约为0.8eV。在低于3.56eV的光激发下,谱带的峰值能量随激发能量的降低明显红移。在安德森带结构和指数分布的带尾态密度的基础上,考虑了尾态中粒子的两种跃迁过程,实验的PL谱就可得到解释。并用这个简单模型计算了这种材料的光致发光谱特征。     

FTIR and optical properties for irradiated PVA–GdCl3 and its possible use in dosimetry

There are various chemical and physical changes caused when polymers are exposed to a source of radiation. In the present work, four films of polyvinyl alcohol (PVA) doped with 2, 4, 6 and 8 wt% of gadolinium chloride (GdCl₃) have been irradiated by low-dose fast neutrons using Am-241/Be-9. The structural properties of the synthesized films have been investigated pre- and post-irradiation on the basis of Fourier transform infrared technique. The optical properties of the PVA–GdCl₃ films have been investigated for doses up to 1.2 KGy. The energy gap of the synthesized films showed a neutron dose dependence and was decreased by 0.81 eV after exposing to 1.2 kGy. At a wavelength of 1000 nm, the refractive index of the PVA doped with 8 wt% GdCl₃ has been increased by nearly 16%. The results suggested the possible use of PVA--GdCl₃ as a dosimeter for the neutron beams.     

Electrical and optical characterization of (PEO+PVAc) polyblend films

Solid polymer blend films based on polyethylene oxide and polyvinyl acetate (PVAc) were prepared in various concentrations by solution cast technique. The features of complexation of the blend films were studied by X-ray diffraction. The electrical conductivity of films was found to increase with increasing PVAc concentration. The conductivity–temperature plots were found to follow Arrhenius nature and showed a decrease in activation energy with increasing PVAc concentration. Optical properties like absorption edge and direct and indirect band gaps were estimated for pure and blend films from their optical absorption spectra. It was found that the energy gap and band edge values shifted to lower energies on blending with PVAc.     

Ultrafast optical power limiting in free-standing Pt–polyvinyl alcohol nanocomposite films synthesized in situ

Free-standing platinum–polyvinyl alcohol nanocomposite films have been prepared by a simple in situ method. By thermal annealing, Pt nanoparticles of different sizes and shapes have been obtained. Their optical nonlinearity is measured using ultrafast (100 fs) laser pulses at 404 nm, in the absorption wing region. A strong optical power limiting is found in the films. The timescale of this limiting action is ultrafast, as it happens within the incident laser pulsewidth. Experimental results and numerical simulation indicate that the sign of the nonlinearity can be controlled by varying the film composition and annealing temperature. Use of ultrashort laser pulses in the free-standing film configuration permits a direct and unambiguous determination of the electronic nonlinearity of the material, since accumulative effects occur at later times lying outside the sharp measurement window.     

Absorption spectra of associates of heterogeneous dye molecules in polymer matrices

The formation processes for heterogeneous associates of cationic dyes in polyvinyl alcohol films are investigated. The influence of colorless anions on the heterogeneous association efficiency is established. The structures of heterogeneous dimers of various dyes in polymer matrixes are defined.     

Structural,optical and electrical properties of laser irradiated Pb doped Ga–Se chalcogenide thin films

Using the Transverse Electrical Excitation at Atmospheric Pressure (TEA) nitrogen laser, we had irradiated the amorphous thin films of Ga₁₀Se₈₁Pb₉ chalcogenide glass and the results have been discussed in terms of the structural aspects of Ga₁₀Se₈₁Pb₉ glass. The observed changes are associated with the interaction of the incident photon and the lone-pairs electrons which affects the band gap. The X-ray structural characterization revealed the amorphous nature of as prepared films and polycrystalline nature of the laser irradiated films. The optical band gap of these thin films is measured by using the absorption spectra as a function of photon energy in the wavelength region 400–1200 nm. It is found that the optical band gap decreases while the absorption coefficient increases with increasing the irradiation time. The decrease in the optical band gap has been explained on the basis of change in nature of films, from amorphous to polycrystalline state, with the increase in exposure time. The dc conductivities and activation energies of these thin films are measured in temperature range 303–403 K. It has been found that the activation energy in Ga₁₀Se₈₁Pb₉ chalcogenide thin films decreases whereas the dc conductivity increases at each temperature by increasing the irradiation time.     

AC impedance studies on proton conducting polymer electrolyte complexes (PVA+CH3COONH4)

A proton conducting polymer electrolytes of pure polyvinyl alcohol and polyvinyl alcohol complexed with ammonium acetate having different compositions have been prepared by solution cast technique. FTIR spectrum confirms the complexation process. The conductivity of the pure polyvinyl alcohol is in the order 10⁻¹⁰ S/cm at ambient temperature and its value increases 10⁴ times when complexed with 20% ammonium acetate. The Arrhenius plot for all electrolyte shows two different regions above and below the glass transition temperature. A high dielectric loss value is observed for the case of complexed PVA in comparison to pure PVA. Based on the study of relaxation spectra, it is found that the relaxation time decreases with increase in temperature and dopant concentration. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Effect of Temperature on the Rate of Triplet–Triplet Annihilation of 1,2-Benzanthracene in a Polymer Matrix

The process of triplet–triplet annihilation (TTA) of 1,2-benzanthracene (1,2-BA) incorporated into polymer films of polyvinyl butyral has been investigated in the temperature interval 80–360 K. An analysis of the kinetics of the decay of delayed annihilation fluorescence (DAF) of 1,2-BA has shown that the process of the triplet excitation energy transfer in a disperse medium of the polymer at distant times of the DAF decay can be described using the approximation of random walks of the triplet energy in the inhomogeneous medium of the polymer. At low temperatures, at the initial times of DAF decay the TTA process is described with the aid of a model of static annihilation.     

一种纳米硅薄膜的传导机制

基于对实验和理论的分析，提出一种异质结量子点隧穿（HQD）模型，并导出了纳米硅薄膜电导率完整的表达式．其主要思想是，纳米硅薄膜中的微晶粒（几个纳米大小）具有量子点特征，在微晶粒与界面之间由于两者能隙的差异构成晶间势垒，这类似于多晶硅中经常使用的晶间势垒模型（GBT）．考虑到量子点中的单电子隧穿特征，认为纳米硅薄膜中的电传导是由微晶粒中电子弹道式输运与单电子越过势垒的隧穿构成的．这就是HQD模型的主要内容，理论结果与实验相符 关键词：     

Specific features of spectra of cyclometalated Pt(II) and Pd(II) complexes in polyvinyl alcohol

The absorption spectra and luminescent properties of ethylenediamine complexes of Pt(II) and Pd(II) with cyclometalating ligands (2-phenylpyridinate and 2-2’-thienyl)pyridinate) in polyvinyl alcohol are studied. It is ascertained that, upon an increase in temperature, the nonradiative degradation of energy in palladium complexes occurs according to the mechanism of strong vibronic coupling, whereas platinum complexes show weak vibronic coupling.