Photoconductivity Studies Research Articles

WITHDRAWN: Investigations on optical, thermal, mechanical and photoconductivity studies on pure and metal doped non linear optical l-Arginine Acetamide single crystals

WITHDRAWN: Investigations on optical, thermal, mechanical and photoconductivity studies on pure and metal doped non linear optical l-Arginine Acetamide single crystals

Crystal growth, spectral, optical, laser damage, photoconductivity and dielectric properties of semiorganic l-cystine hydrochloride single crystal

The semiorganic single crystals of l-cystine hydrochloride have been grown by slow evaporation solution growth technique at 40°C. The grown crystals were subjected to single crystal XRD, FTIR, optical absorbance, laser damage threshold, photoluminescence, photoconductivity and dielectric studies. Single crystal XRD studies reveal that the crystal belongs to monoclinic system with space group C2 and the lattice parameters are a=18.63 (Å), b=5.28 (Å), c=7.26 (Å), α=90°, β=103.70°, γ=90° and V=696 (Å3). FTIR spectroscopy confirms that a band at 1731cm−1 represents characteristic of α-amino acid hydrochlorides. The UV–Vis–NIR absorption spectrum was analyzed and the optical band gap energy was found to be 3.8eV. The crystal exhibits sharp emission peak at 388nm. The thermal characteristics of crystals were studied by TG-DTA, which indicate that there is no weight loss up to 201°C. Surface laser damage threshold value of title compound was estimated using high power Q-switched Nd:YAG laser operating at 1064nm. Dielectric and photoconductivity studies were also carried out for the grown crystals.

Studies on the growth and characterizations of 2-amino 4-methylpyridinium tartrate monohydrate single crystals

A noncentrosymmetric, organic single crystal, 2-amino 4-methylpyridinium tartrate monohydrate was synthesized and grown by slow evaporation solution technique at room temperature using methanol as a solvent. The cell parameters of the grown crystal were determined by single crystal X-ray diffraction method. The various functional groups present in the crystal and the different types of protons and carbons were identified by the FTIR and NMR spectral analyses. Optical properties were determined by UV–vis–NIR spectroscopic and photoluminescence studies. The second harmonic generation of the grown crystal was observed by Kurtz Perry powder technique. Photoconductivity studies were carried out for various voltages applied on the grown crystal. The thermal and mechanical stabilities of the 2-amino 4-methylpyridinium tartrate monohydrate single crystal were investigated by TGA–DTA and Vickers microhardness measurements, respectively.

Investigation on Physical Properties of Semiorganic Nonlinear Optical Glycine Zinc Sulfate Single Crystal

Nonlinear optical single crystals of Glycine Zinc Sulfate (GZS) were grown by slow evaporation technique. Single crystal X-ray diffraction analysis revealed the crystal system and lattice parameter values. Powder X-ray diffraction analyses have been carried out and the diffraction patterns have been indexed. The optical properties of the crystals were determined using UV-Visible spectroscopy. Optical constants such as band gap, refractive index, extinction coefficient and electric susceptibility were determined from UV-Visible spectroscopy. The refractive index was determined using Brewster's angle method. Hardness of the GZS crystal was estimated by Vicker's hardness studies. Second Harmonic Generation (SHG) of GZS crystal was investigated by Kurtz powder technique. The dielectric constant and dielectric loss measurements were carried out for different temperatures and frequencies. The photoconductivity studies confirm that the grown crystal has negative photoconductivity nature. In order to investigate the growth mechanism and surface features, etching studies are carried out for the crystal.

English

Zinc selenide (ZnSe), zinc sulphide (ZnS) and lead sulphide (PbS) thin films were prepared by chemical bath deposition (CBD) method. In this paper we report results on the photoconductivity behaviour of ZnSe, ZnS and PbS thin films. Photoconductivity measurements were carried out at room temperature by connecting it in series with a picoammeter (Keithley 480) and a dc power supply. Photoconductivity processes may be the most suitable technique for obtaining information about the states in the gap. The thin films showed a significance rise in photocurrent over dark current. The photoconductive studies reveal the positive photoconductive nature of the thin films. Photoconduction includes generation and recombination of carriers and their transport to the electrodes.    Key words: Thin films, photoconductivity, ZnSe, ZnS, PbS. &nbsp

Synthesis, growth, structural and HOMO and LUMO, MEP analysis of a new stilbazolium derivative crystal: A enhanced third-order NLO properties with a high laser-induced damage threshold for NLO applications

A new organic third-order nonlinear optical crystal from stilbazolium family 2-[2-(4-methoxy-phenyl) vinyl]-1-methyl-pyridinium tetrafluoroborate (4MSTB) has been synthesized and grown by slow evaporation method for the first time. The grown crystal structure was confirmed by single crystal X-ray diffraction analysis, and it is revealed that the grown crystal crystallized in a triclinic crystal system with centrosymmetric space group P1¯. The HOMO and LUMO energies were calculated for the grown crystal explains charge transfer takes place within the molecule and confirms the suitability of the title crystal for NLO applications. The presence of various vibration modes of expected functional groups was identified by FT-IR analysis. The transmittance ability of the grown crystal was also analyzed by using UV–Vis–NIR spectral studies and shows that the crystal has no absorption of light in the entire Vis–NIR region. The thermal stability of the title crystal has been investigated by TGA/DTA studies and revealed that the material was thermally stable up to the melting point, 193°C. The hardness number, Meyer index, yield strength, and elastic stiffness constant has been estimated for the grown 4MSTB crystal using Vickers microhardness tester. Photoluminescence excitation studies showed green emission radiation occurred at 517nm. The dielectric properties of the grown crystal have been analyzed as a function of temperature over a wide range of frequency (50Hz–5MHz) by using LCR meter. The result of ac electrical conductivity of 4MSTB was found to be 5.25×10−5 (Ωm)−1. The laser damage threshold (LDT) energy for the grown crystal has been measured by using a Q-switched Nd:YAG laser as a source in single-shot mode (1064nm, 10Hz, 420mJ). The result of LDT indicates that grown title crystal has excellent resistance to laser radiation than those of known some inorganic NLO materials. The chemical etching studies were carried out to assess the perfection of the grown crystals. Its third-order nonlinear optical properties were investigated by Z-scan technique and proved that the 4MSTB crystal possesses two-photon absorptions (TPA) and the self-defocusing effect. The second-order molecular hyperpolarizability (γ) value at 632.8nm is calculated to be 3.555×10−34esu. The photoconductivity study of 4MSTB reveals that the negative photoconducting nature. The obtained all the results in the present work are making a 4MSTB promising candidate for the possible applications in optical switches, optical power limiter, and non-linear optical applications.

Fabrication and performance study of electro-optical modulator and third order nonlinearity using unidirectional method (Sankaranarayanan–Ramasamy) grown Imidazolium l-Tartrate 〈0 1 0〉 single crystal

The results of electro-optical modulator and third order nonlinearity of an organic single crystal of Imidazolium l-tartrate (IMLT) 〈010〉 grown by unidirectional growth method of Sankaranarayanan–Ramasamy (SR) are discussed for the first time in literature. The grown IMLT seed crystals were characterized by single crystal XRD and the lattice parameters were confirmed. The UV–Visible transmittance analysis shows that SR method grown IMLT single crystal possesses good transmittance in the entire visible region with a low cut-off wavelength at 240nm. The mechanical study on the (010) plane of the IMLT single crystal analyzed by Vickers microhardness tester reveals the moderate hardness of the material. Photoconductivity studies on pure IMLT single crystal enumerated the positive photoconducting nature. Refractive index of the IMLT single crystal was determined by Brewster angle method. Second Harmonic Generation (SHG) efficiency of IMLT is 4.3 times greater than the standard Potassium Dihydrogen Phosphate (KDP) crystal. Nonlinear refractive index (n2), nonlinear absorption coefficient (β) and third-order nonlinear optical susceptibility χ(3) were evaluated using Z-scan method. The half wave voltage and electro-optical coefficient of IMLT crystal were determined using polarimetric technique. The electro-optical coefficient (r12) of IMLT is found to be greater than that of KDP crystal which represents the suitability of IMLT crystal to design the electro-optical modulator with low half wave voltage for nonlinear optical applications.

Growth, structural, optical, electrical and mechanical studies on urea phthalic acid single crystals

Optically good quality organic crystals of urea phthalic acid (UPA) were grown successfully by slow evaporation solution growth technique at room temperature. The crystalline nature of the crystal was assessed by powder XRD analysis. The presence of various functional groups has been identified by using FT-IR spectral analysis. UV–vis spectra show good transparency in the entire visible region. Dielectric constant and dielectric loss were measured for the grown crystals. Photoconductivity studies were also taken for the grown crystals. Mechanical studies of the crystals were studied using Vickers microhardness tester.

Effect of Trisodium Citrate Concentration on the Structural and Photodiode Performance of CdO Thin Films

CdO thin films were deposited on glass and silicon substrates by simple perfume atomizer at 350°C using cadmium acetate and trisodium citrate (TSC). The effect of the TSC concentration on the structural, morphological, optical, and photoconductive properties of the prepared CdO thin films was investigated. X-Ray diffraction (XRD) studies of the deposited films revealed improvement in crystalline nature with increase of TSC concentration. Films prepared without TSC showed porous nature, not fully covering the substrate, whereas films prepared using TSC exhibited full coverage of the substrate with uniform particles. Optical transmittance study of the films showed high transmittance (50% to 60%), and the absorption edge was found to shift towards the red region depending on the TSC concentration. The films exhibited a direct band-to-band transition with bandgap varying between 2.31 eV and 2.12 eV. Photoconductivity studies of the n-CdO/p-Si structure for various TSC concentrations were also carried out. I–V characteristics of this n-CdO/p-Si structure revealed the formation of rectifying junctions, and its photoconductivity was found to increase with the TSC concentration.

Synthesis of simple and novel biocomposite doped nanocrystalline tin oxide and its humidity sensing properties

The Hygrophila Spinosa T. Anders (HST) plant seed that contains mineral constituents were doped in SnO2 prepared by the conventional method. The structural parameters, functional groups, surface morphology, elemental analysis and optical behavior of the prepared samples was made using X-ray diffraction, Fourier transform-infra red, scanning electron microscope, energy dispersive X-ray analysis, diffuse reflectance spectroscopy techniques respectively have been studied. XRD-surface area for all the samples was obtained from the Williamson–Hall plot. Photoconductivity studies were carried out for all the samples prepared with different HST composition in SnO2. The negative photoconductivity was observed for the HST doped SnO2 and HS samples, except pristine SnO2. The SH2 sample with high specific surface area shows good response and recovery characteristics toward humidity.

Electrical and photoconductivity studies on AgSbSe2 thin films

Silver antimony selenide thin films have been deposited on ultrasonically cleaned glass substrate at a vacuum of 10−5 torr using reactive evaporation technique. The preparative parameters like substrate temperature and incident fluxes have been properly controlled in order to get highly reproducible compound films. The polycrystalline nature of the sample is confirmed using XRD. The dependence of the electrical conductivity on the temperature has also been studied. The prepared AgSbSe2 samples show p-type conductivity. The samples show a little photoresponse.

Growth, optical, electrical and photoconductivity studies of a novel nonlinear optical single crystal: Mercury cadmium chloride thiocyanate

SCN− ligand based organometallic non-linear optical mercury cadmium chloride thiocyanate (MCCTC) crystals are grown from water plus methanol mixed solvent by slow evaporation technique. The grown crystals are confirmed by single crystal X-ray diffraction analysis which reveals that the MCCTC belongs to rhombohedral system with R3c space group. MCCTC exhibits a SHG efficiency which is nearly 17 times more than that of KDP. The dielectric constant, dielectric loss measurements of the sample have been carried out for different frequencies (100 Hz to 5 MHz) and, temperatures (308 to 388 K) and the results are discussed. Photoconductivity study confirms that the title compound possesses negative photoconducting nature. The surface morphology of MCCTC was also investigated

Fano resonances in photoconductivity spectra of hydrogen donors in ZnO and rutile

The results of photoconductivity studies of hydrogen donors in ZnO and rutile TiO2 are presented. It is shown that local vibrational modes of O–H bonds comprising donors in both semiconductors can be detected in photoconductivity spectra as Fano resonances at 3611 and 3290 cm−1 in the case of ZnO and TiO2, respectively. The frequencies of these features red-shift in energy down to 2668 (ZnO) and 2445 cm−1 (TiO2) if hydrogen is substituted by deuterium. Based on the frequency of the deuterium resonance it is concluded that the ionization energy of the hydrogen donor in TiO2 is less than 300 meV, which is in variance with predictions of theory. The reasons for such a discrepancy are discussed.

Study on third order nonlinear optical properties of a metal organic complex—Monothiourea–cadmium Sulphate Dihydrate single crystals grown in silica gel

The third order nonlinear optical properties of Monothiourea–cadmium Sulphate Dihydrate crystal were measured using a He–Ne laser (λ=632.8nm) by a Z-scan technique. The magnitude of nonlinear refractive index (n2) and nonlinear absorption coefficient was found to be 4.4769×10–11m2/W and 1.233×10−2m/W respectively. The third order non-linear optical susceptibility χ(3) was found to be in the order of 3.6533×10−2esu. The negative sign of non-linear refractive index shows the self-defocusing nature of the gel grown crystal. The second-order molecular hyperpolarizability γ of the grown crystal is 1.2822×10−33esu. Laser damage threshold was measured by using an Nd: YAG laser (1064nm). Photoconductivity studies of the gel grown crystal revealed that the crystal possesses positive photoconducting nature. The results obtained from Z-scan, laser damage threshold and photoconducting studies reveal that the crystal can be a possible candidate material for photonics device, optical switches, and optical power limiting application.

Investigation on growth, structure and characterization of succinate salt of 8-hydroxyquinoline: An organic NLO crystal

8-Hydroxyquinolinium succinate (8-HQSU) has been synthesized and single crystals were grown from ethanol solvent by employing the technique of slow evaporation at room temperature. The structure of the grown crystal has been elucidated by single crystal X-ray diffraction analysis. It reveals that 8-HQSU crystallizes in monoclinic system with non-centro symmetric space group P21. FTIR, 1H and 13C NMR spectral investigations have been carried out to identify the vibrational modes of various functional groups and placement of proton and carbon in the 8-HQSU compound, respectively. UV–vis–NIR transmission spectrum shows the cutoff wavelength around 357nm. In addition, a photoluminescence spectral analysis was carried out for 8-HQSU crystals. The thermal properties of crystals were evaluated from TGA and DTA techniques and the crystal was found to be stable up to 145°C. The dielectric studies show that the dielectric constant and dielectric loss decrease exponentially with frequency at different temperatures. Photoconductivity studies were carried out on the grown crystals it reveals the positive photo conducting nature. Powder second harmonic generation property of the crystal was confirmed by Kurtz and Perry powder SHG technique and it is found to be 1.3 times greater than that of KDP.

Photoconductivity Measurements in Nanostructured ZnO and ZnO:Al Films

ZnO is a versatile material used in numerous applications, such as antireflective coatings, transparent electrodes for solar cells, gas sensors, varistors and electro and photoluminescent devices. One of the most important properties of ZnO is the photoconductivity in the UV, due to the band-gap energy.In this work, nanostructured pure and aluminium doped ZnO films were grown by sol-gel method. The precursor solutions were deposited with a different quantity of layers by spin-coating technique on SiO2 substrates.The films were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Photoconductivity study of prepared films showed that layers also exhibit sensitivity in the visible spectrum besides a remarkable and usual sensitivity to UV. Performance of pure and doped ZnO films was compared. The UV sensitivity related to the film thickness was also studied.

Fractional photo-current dependence of graphene quantum dots prepared from carbon nanotubes.

We report on the photo-conductivity studies of chemically synthesized graphene quantum dots (GQDs) of average size 12 nm obtained by the oxidative acid treatment of MWCNTs. The dependence of photocurrent Iph (Iph = Iill - Idark) on the laser intensity P under a wide range of laser intensities (5 mW ≤ P ≤ 60 mW) shows a fractional power dependence of Iph on light intensity. The temperature dependence (300 K < T < 50 K) of Iph observed in thin films of these GQDs indicates that in the higher temperature region (T > ∼100 K), as the temperature increases, the number of thermally generated carriers increase resulting in increased Iph. At sufficiently low temperatures (T ≤ 100 K), a constant Iph is observed, indicating a constant photo-carrier density. Such a behavior is typically observed in many photoactive disordered semiconductors, which are often used in a variety of applications. We believe that the investigations presented here will enhance our understanding of the photocurrent generation phenomenon in chemically obtained GQDs.

Fluorescence resonance energy transfer and surface Plasmon resonance induced enhanced photoluminescence and photoconductivity property of Au–TiO2 metal–semiconductor nanocomposite

In this manuscript, we have successfully synthesized Au–TiO2 nanocomposite by sol–gel process. Photoluminescence (PL) and photoconductivity (PC) study have been performed on both bare TiO2 and Au–TiO2 composite samples. We observe enhancement of photoluminescence emission in Au–TiO2 nanocomposite compared to bare TiO2. The enhanced photoluminescence is ascribed owing to combined influence of fluorescence resonance energy transfer and surface Plasmon resonance effect due to presence of Au nanoparticles in nanocomposite sample. Also this nanocomposite exhibits enhanced UV photocurrent because of fluorescence resonance energy transfer by metallic Au attached with TiO2. Interfacial charge transfer can also be realized by the electrochemical impedance spectroscopy results.

Erratum to: Crystal growth, structural, optical, thermal and electrical properties of organic NLO l-arginine acetamide single crystal

Optically, good-quality single crystals of l-arginine acetamide (LAAM) are grown by slow evaporation method. Single-crystal X-ray diffraction analysis reveals that the crystal belongs to monoclinic system. The FTIR spectrum is used to confirm various functional groups present in the grown crystal. The optical absorption studies show that the crystal is transparent in the entire visible region with a cutoff wavelength of 350 nm. The thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) of l-arginine acetamide crystal are performed by using TG/DSC instrument. The DSC trace shows a peak at 270 °C which corresponds to the melting point of l-arginine acetamide crystal. Dielectric constant measurements are taken at different temperatures and frequencies. Photoconductivity studies show that the dark current is always higher than the photocurrent, thus confirming the negative photoconductivity. Nonlinear optical property of the grown crystal LAAM is confirmed by Kurtz and Perry technique.

Growth, mechanical, dielectric, thermal and optical studies of a nonlinear optical crystal: l-Histidinium dipicrate dihydrate

Nonlinear optical single crystals of l-histidinium dipicrate dihydrate (LHDPDH) were grown by slow evaporation solution growth technique at room temperature. The microstructure and growth features were analysed by chemical etching. The grown crystal was subjected to X-ray diffraction analysis to confirm its purity and crystal structure. Mechanical behaviour of the grown crystal was analysed by Vicker's microhardness test. The stiffness constant was evaluated for various loads. The dielectric behaviour was investigated at different frequencies and temperatures. AC conductivity and activation energy were determined. Electronic properties, such as valence electron plasma energy, average energy gap or Penn gap, Fermi energy and electronic polarizability were calculated. Thermal analysis confirmed the association of two water molecules in the crystal lattice of LHDPDH and revealed the thermal stability of the crystal. Photoconductivity study reveals that LHDPDH exhibits positive photoconductivity. The optical transmission window and optical band gap of the crystal were found by UV–vis–NIR studies. Second harmonic generation efficiency was found to be 2.5 times that of the standard KDP crystal. The laser damage threshold for the grown crystal was measured using Nd:YAG laser.