Polymers with different azobenzene moiety for NLO application

Date du colloque&nbsp;: 06/2010</p

Temperature Dependence of the Bistable Photoconductivity of Thin DNA: PEDOT Films

Thin DNA: PEDT-PSS layers were investigated. The functionalization of DNA by PEDT-PSS rendered the material electrically active, its conductivity being about (1-5) x 10(-10) Omega(-1)cm(-1) at the room temperature. The samples remained ohmic down to 77 K. The thermal activation energy of the conductivity near the room temperature was about 0.033 eV, and it decreased under 0.014 eV below 170-180 K. The weak carrier trapping was identified by the Thermally Stimulated Current method, proving the recombination of light-generated carriers. Notably, by constant light excitation a "bistable" photoconduction below the room temperature was evidenced. The photosensitive state could be induced by the light from the spectral region from similar to 500 nm up to similar to 1000 nm, with a maximum effect in the range of 650-800 nm. A remarkable increase of the photocurrent could be observed below 145-155 K by cooling the samples. Meanwhile by heating the photosensitivity remained increased up to 235-245 K. The long characteristic relaxation times after the light excitation in this state were proportional to the relative photosensitivity of material. This indicates that such phenomenon could presumably be attributed to the light-induced changes associated with PEDT-PSS, i.e., modification of the sample material morphology and/or induced variation of carrier transport conditions

NLO properties of functionalized DNA thin films

In this paper we investigate the third-order nonlinear optical properties of spin deposited thin films of DNA-based complexes using the optical third harmonic generation (THG) technique at a fundamental wavelength of 1064 nm. We found that the third-order susceptibility, χ(3)(− 3ω;ω,ω,ω), of DNA-based films was about one order of magnitude larger than that of our reference, a pure silica slab. In thin films doped with 5% of the chromophore disperse red 1 (DR1), a two order of magnitude larger value of χ(3)(− 3ω;ω,ω,ω) was observed

Investigation of functionalised thin films of DNA:PEDT-PSS - electrical and optical properties

We have investigated electrical, charge transport and optical properties of functionalised DNA:PEDT-PSS thin films. Current-voltage dependencies of the samples were linear and symmetrical down to 77 K temperature. Material conductivity at room temperature was about (1-5)Ã10-10 ¿-1 cm-1. The thermal activation energy of the conductivity measured in the dark was about 0.033 eV near the room temperature independently on the applied bias. The weakly expressed carrier trapping was identified by the thermally stimulated current method, evidencing the fast recombination of light-generated carriers. Though, at constant light excitation a "bistable" photoconduction below the room temperature was identified. I.e., upon excitation by light from the spectral region 500 800 nm a notable increase of the photocurrent could be observed below 140 160 K by cooling the samples. Meanwhile by heating the photosensitivity remained increased up to 230 240 K. Most probably such phenomenon could be attributed to the light-induced morphology changes of the samples

Amplified spontaneous emission of Rhodamine 6G embedded in pure deoxyribonucleic acid

Deoxyribonucleic acid (DNA) is commonly viewed as a genetic information carrier. However, now it is recognized as a nanomaterial, rather than as a biological material, in the research field of nanotechnology. Here, we show that using pure DNA, doped with rhodamine 6G, we are able to observe amplified spontaneous emission (ASE) phenomenon. Moderate ASE threshold, photodegradation, and reasonable gain coefficient observed in this natural host gives some perspectives for practical applications of this system in biophotonics. Obtained results open the way and will be leading to construction of truly bio-lasers using nature made luminophores, such as anthocyanins

Analysis of Electrical and Optical Properties of DNA:PDT-PSS Thin Films

We report investigations of functionalized DNA:PEDT-PSS films. The electrical conductivity of the sample material at the room temperature was about (1–5)*10-10 Ω-1cm-1. The IV curves of the samples were linear and symmetrical in the region from the room temperature down to the liquid Nitrogen temperature. The thermal activation energy of the conductivity near the room temperature was about 0.033 eV independently on the applied bias. The weak carrier trapping was identified by the Thermally Stimulated Current method, proving the fast recombination of light-generated carriers. Notably, by constant light excitation a “bistable” photoconduction below the room temperature was evidenced. I.e., upon excitation by a white light a remarkable increase of the photocurrent could be observed below 145–155 K by cooling the samples. Meanwhile by heating the photosensitivity remained increased up to 235–245 K. Such phenomenon could presumably be attributed to the light-induced morphology changes of the sample material

Functional Properties of Thin Films of Deoxyribonucleic Acid with Poly(3,4-ethylenedioxythiophene) and Poly(styrenesulfonate) Complex and Bistability of Their Photocurrent

Functional photo- and electrical properties of thin films of DNA:PEDT-PSS were investigated. The sample current-voltage dependencies were linear and symmetrical down to liquid nitrogen temperature; the sample conductivity at 300 K was found to be 10(-10) Omega(-1)cm(-1). The thermal activation energy of the dark conductivity was about 33 meV independently on the applied bias in the temperature region between 200 K and 300 K. Carrier trapping was evidenced by the Thermally Stimulated Current method. Nevertheless this effect was weakly expressed, most probably because of the fast recombination of generated carriers. Notably, a bistable photoconduction behaviour was identified below the room temperature at constant light excitation. Upon illumination of the samples by similar to 500 nm - 800 nm light a marked increase of the photocurrent took place by cooling them below 140 K - 160 K. In contrast, by heating the photosensitivity remained increased up to 230 K - 240 K. This effect could be associated with the light-induced modification of charge transport conditions in the samples

Biopolymer-based material for optical phase conjugation

We present results of optical phase conjugation experiments in modified DNA (deoxyribonucleic acid) - dye system. The system consisted of a biopolymeric matrix made of DNA blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride (CTMA) and doped with a photochromic dye Disperse Red 1. Results were obtained in a typical degenerate four wave mixing experiment. For sample excitation we used linearly polarized light at a wavelength 514.5 nm, delivered by an argon ion (Ar+) laser. The phase conjugated signal which emerged from the sample had rise and fall time constants of a few milliseconds with an excellent reversibility

Amplified spontaneous emission in the spiropyran-biopolymer based system

Amplified spontaneous emission (ASE) phenomenon in the 6-nitro-1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indolin] organic dye dispersed in a solid matrix has been observed. The biopolymer system deoxyribonucleic acid blended with cationic surfactant molecule cetyltrimethyl-ammonium chloride served as a matrix. ASE appeared under sample excitation by UV light pulses (λ=355 nm) coming from nanosecond or picosecond neodymium doped yttrium aluminum garnet lasers and has been reinforced with green (λ=532 nm) light excitation followed UV light pulse. The ASE characteristics in function of different excitation pulse energies as well as signal gain were measured