Photoconductivity Studies Research Articles

Photoinduced modulation and the effect of CNT loading on field effect transistor characteristics of CNT/ZnO/PVDF composite.

Carbon nanotube (CNT)/ZnO/ polyvinylidene fluoride (PVDF) polymer composite phototransistor is studied for the effect of CNT loading and the photoinduced modulation on its transfer characteristics. XRD study shows that the induced strain in the composite is due to the addition of CNT to the ZnO/PVDF composite. The percentage ofβ-phase present in PVDF is estimated through Raman spectroscopy and the composite's spectral response is determined by UV-Vis absorbance spectroscopy. From the DC electrical conductivity study it is found that the percolation threshold for the composites is obtained for 0.3 wt% of CNT, and 0.44 wt % of CNT loading makes the composite conductive. On adding 1 wt% of CNT, the electrical conductivity of the ZnO/PVDF composite increases 40 times (∼0.2μS m-1). The temperature-dependent DC conductivity shows that the conductivity of the composites changes from variable range hopping to band conductance upon an increase in CNT loading above the percolation threshold and exhibits a negative temperature coefficient. Two terminal photoconductivity studies are done to understand the photo enhancement and sensitivity of all the devices. PE hysteresis studies show that the polarization of the composites increases drastically from 0.05μC cm-2below the percolation threshold to 10-30μC cm-2above the percolation threshold of CNT in the composite. To study the effect of interfacial polarization on photoconductivity, the composite is studied in a three-terminal device format using SiO2as a gate dielectric. A band diagram analysis of the oxide-composite and CNT/ZnO interface is done to understand the mechanism behind the photoinduced field effect on transfer characteristics and the effect of CNT loading. The switching behavior and decay time under UV illumination are studied to understand the effect of CNT loading and photoinduced polarization. The persistent photoconductivity decreases and the charge collection efficiency of the FET increases as the CNT loading increases.

Study of Photoconductivity of Thin Films of Cadmium and Selenium Obtained by Chemical Deposition

In this work, the photoconductivity (PC) spectrum of thin CdSe films was studied. In the course of studies on glass substrates, thin films of cadmium and selenium with a thickness of h = 200 nm and h = 400 nm were selected. The thickness of the samples obtained by chemical deposition was determined by the gravimetric method. Since CdSe crystal is a light-sensitive semiconductor material, the photoconductivity of thin films has been studied. The spectra obtained during studies carried out at a wavelength λ = 600-1100 nm were analyzed. It has been established that the spectrum is chaotic, since in the h = 200 nm layers the phase is not completely formed. In the layers h = 400 nm, a maximum centered at the wavelength λ = 710 nm was recorded.

Nucleation, crystal growth, XRD, optical, electrical, PC, SEM, SHG and Z-scan analysis of LHPP for NLO and optical limiting application

High-quality organic L-histidinium 4-nitrophenolate 4-nitrophenol (LHPP) single crystals were grown using an aqueous solution. The crystals were grown using slow evaporation solution technique (SEST) at a temperature of 40°C using a constant temperature bath (CTB). Nucleation growth rates were monitored for various durations using an optical microscope. The crystalline perfection was confirmed through sharp, high-intensity diffraction peaks observed in the theoretical and experimental powder X-ray diffraction (PXRD) analysis, which also confirmed the monoclinic crystal structure with the noncentrosymmetric P21 space group. The crystallite size and strain were calculated using Williamson–Hall coefficient. Vibrational frequency assignments of LHPP were determined using FTIR spectroscopic analysis. Optical properties were studied using UV–Vis NIR spectroscopic studies, which showed that the crystals have very low absorption and high transmittance in the entire visible region. Additionally, the optical energy bandgap (Eg) was calculated and found to be 6.15[Formula: see text]eV. Luminescence properties were studied using fluorescence (FL) analysis. Dielectric investigations were subjected to varying frequencies to study the suitability of the crystal for transistor application. The positive photoconductive (PC) nature of the crystal was confirmed using photoconductivity studies to confirm suitability for photodetector devices that measure the intensity of light rays. Etching studies revealed the growth pattern and the formation of different kinds of etch pits. The surface morphology was studied using scanning electron microscopy (SEM) and electrochemical studies were also carried out. The relative second harmonic generation (SHG) efficiency of the material was also examined and found to be 1.34 times that of standard KDP. The optical limiting and higher-order nonlinear optical (NLO) properties of the grown crystals were studied by the [Formula: see text]-scan method using a Nd: YAG laser functioning at 532[Formula: see text]nm.

Supernanoporous SnO2 particles and spheres as sustainable solar cell constituents

This study presents the synthesis and a comparative report of the properties of supernanoporous SnO2 particles SNSP (0D) supernanoporous SnO2 spheres SNSS (3D) formed with an assembly of SNSP with a view to examine their application as effectual photoanodes in sustainable solar energy conversion. Porosity imposed nanoparticles with extended surface area improve photon interaction and charge transfer by increasing the absorption of light, hence addressing the existing efficiency hurdles in solar cells. SNSP with particle size of ∼23 nm and SNSS with particle size and sphere size of ∼26 nm and ∼800 nm, respectively, were synthesized by treating SnCl4 via solvothermal process at different experimental conditions. Important aspects of the as-synthesized SNSP and SNSS samples, such as the crystal structure, particle size, optical behaviour, identification of elements present, were characterized by powder X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Ultra Violet Diffuse Reflectance Spectroscopy (UV-DRS) and Energy Dispersive Analysis X-ray (EDAX) Spectroscopy techniques. Field dependent dark and photoconductivity studies reveal significant rise in the photoconducting nature, opto-electrical and surface properties of SNSP and SNSS. Pore size distribution and specific surface area of SnO2 particles and spheres were measured by Brunauer-Emmett-Teller (BET) analysis. High Resolution Transmission Electron Microscopy (HRTEM) is performed to analyze the size and shape of the porous SnO2 particles and spheres and further to correlate the data derived from FESEM. From other prevailing applications of porosity imposed nanomaterials such as gas sensing, catalytic and photodegradation the innovation of this work is to depict the novelty of porous SnO2 particle and sphere with highlighting thermal stability to instigate into the charge transport property suitable for solar cell application. The results were analyzed evincing the photovoltaic properties of spheres over particles and hence the PSC constituent among SNSP and SNSS with better proficiency was identified as appropriate photoconducting medium for fabrication of sustainable photovoltaic cells.

The growth aspects and experimental techniques for the characterization of amino acid L-histidine hybrid crystals for nonlinear optical device applications

The development of crystal growth and measurement methods opens new possibilities for studying materials with remarkable nonlinear optical features. The development of bulk crystals is a constant concern to be beneficial for device applications. This study focuses on the development of nonlinear optical crystals of l-histidine complexes, characterization approaches, and prospective applications. The solution growth approach, a straightforward, inexpensive, and low-temperature growth technique, was adopted broadly. Recent studies show that l-histidine derivatives have potential optical, SHG, thermal, dielectric, and mechanical properties, making them an excellent choice for nonlinear optical devices. In this work, structural, spectroscopic, chemical composition, linear and nonlinear optical analyses, thermal, and dielectric characterizations of l-histidine derivatives were conducted. Most of the l-histidine complexes were found to be crystallized in orthorhombic and monoclinic crystal systems with P212121 and P21 space groups. The crystalline perfections of the samples were analyzed by the HR-XRD method. The energy-dispersive X-ray (EDX) spectroscopic technique was applied to evaluate the chemical content of the compounds. FT-IR and FT-Raman techniques were used to recognize the molecular vibrations and functional groups of the l-histidine derivatives. The UV-visible and photoconductivity studies were done to examine the optical behaviors of the developed crystals. Most of the crystals were found to have excellent optical transparency and wide bandgaps. It has been observed that l-histidine hydro-fluoride dehydrate and l-histidine tetrafluoroborate are found to have the highest second harmonic generation (SHG) efficiencies. The dielectric analyses were utilized to study the dielectric constant and dielectric loss variations with the applied frequency. According to the thermal analyses, most of the crystals were found to have substantial thermal stabilities suitable for device applications.

Low temperature dielectric study and photoconductive analysis of ZnO/NiO composite material

The sol-gel process was used to synthesize a ZnO–NiO composite material in this study. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the material, which confirmed the existence of both ZnO nanoparticles and NiO sheets in the composite. The composite material contained two distinct crystalline phases, the face-centered cubic phase of NiO and the hexagonal phase of ZnO. The composite's average crystallite size was determined to be 19.0 nm. The particle size of the composite material was calculated to be ∼121 nm. The band edge emission at 393 nm (3.15 eV) was measured using photoluminescence (PL) spectroscopy. The PL spectrum revealed other emissions as well. The dielectric properties of the material were studied at low temperatures in the frequency range of 20 Hz to 1 MHz, and it was found to have a low dielectric dissipation at high frequencies, making it suitable for use in high frequency microwave devices. Impedance data was fitted using Z-View software with a fitting error of <5%. Impedance spectroscopy revealed that the composite material had two dielectric relaxation processes related to the bulk and the grain boundary. Analysis of frequency dependent ac conductivity revealed Overlapping large-polaron hopping (OLPH) is responsible conduction mechanism in our case indicated by variation of temperature (200–280 K) dependent parameter “s” with temperature. Photoconductivity studies showed that the composite material had enhanced electrical conductivity and photoconductivity compared to pure ZnO and NiO. This makes it a promising candidate for use in optoelectronic applications such as solar cells, optical switches, and photodetectors. The responsivity of composite (0.86 mA/Watt) is found to be 10 times greater than that of the responsivity of NiO (0.085 mA/Watt).

Optical and electrical properties of Ni+2 doped nanocrystalline Bi2S3 thin films prepared by chemical bath deposition method

Nickel (Ni+2) doped nanocrystalline Bi2S3 thin films are deposited on the glass substrate from the solutions containing Bismuth Nitrate, Ethylenediamine Tetraacetic acid (EDTA) and Thioacetamide at a bath deposition temperature of 318K. The optical, surface morphological and electrical properties of Ni-doped Bi2S3 thin films prepared at three different doping concentration are investigate by using ultraviolet–visible transmission spectra (UV–Vis), Scanning electron microscopy (SEM), Energy Dispersive X-ray (EDAX) and thermo-e.m.f. techniques. The optical band gap energies are found in between 2.32-2.43 eV. The SEM images show that the prepared films are continuous, dense and distributed over the entire area with good uniformity. The electrical conductivity of the films are in the order of 10-2 Ω-1 m-1 . The films are n-type as determined from the Hot Probe method. Photoconductivity studies reveal that photocurrent increases with the increase in Ni doping concentrations. Due to the absorption of photons, free electron-hole pairs (EHP) are produce.

An extensive investigation of the structural, spectral, optical, electrical, and nonlinear optical properties of a single crystal of Di-aqua nitrato bis L-valine lead (II) nitrate

Solvent evaporation has been used to successfully develop the nonlinear optical single crystal di-aqua nitrato bis l-valine Lead (II) Nitrate (DNBLVLN). The grown crystal of DNBLVLN in the orthorhombic system with the non-centro symmetric P1 space group is confirmed by X-ray diffraction study. FTIR and NMR spectral studies showed that DNBLVLN contains a several functional groups. The UV–visible spectrum of the crystal was measured in order to confirm its optical properties. The photoconductivity study reveals the positive photo current in the grown crystal. The fluorescence spectrum reveals that the emission occurs at a wavelength of 492 nm.The presence of Lead (II) Nitrate in l-Valine is confirmed with the EDAX graph and HR-SEM pictures also recorded. The grown crystal's dielectric property was investigated at various temperatures. The second harmonic and third harmonic generation in DNBLVLN crystal has been investigated using the Kurtz-powder method. The open aperture Z-scan approach is used to determine the nonlinearity coefficient (β), which is due to two-photon absorption phenomena and it yields a value of 0.7 × 10− 11 m/W. With a fluence threshold of 6.21 × 1012 W/m2, the associated optical limiting behavior makes the DNBLVLN a potentially useful optical limiting device.

Probing the effect of precursor concentration on the growth and properties of titanium dioxide nanocones for environment safe solar cells.

Environment friendly third-generation solar cells sensitized by dyes, quantum dots, and perovskites are seen as promising energy alternatives. Among the various strategies, employing one-dimensional nanostructures that exemplify the smallest dimension for efficient carrier transport rate from the active layer to electron transport layer (ETL) in photovoltaic devices is attempted in this work. We herein report the synthesis of well-aligned 1-D TiO2 nanocones as ETL for photovoltaic thin films by varying the precursor concentration (0.03M, 0.04M, 0.05M) to track the evolution of growth. The hydrothermal approach is exploited to grow oriented rutile TiO2 nanocones on fluorine doped tin oxide (FTO) under neutral conditions. The examination of phase, crystallinity, morphology, and opto-electronic properties of the well-structured nanocone arrays is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), ultra violet diffuse reflectance spectroscopy (UV-DRS), Brunnauer-Emmett-Teller (BET) surface area analysis, and field-dependent dark and photoconductivity analysis. The XRD pattern confirms the formation of the tetragonal rutile phase. SEM micrographs and UV-DRS spectroscopy reveals that the length of the nanocones and the energy gap is found to be maximum for 0.04M concentration with a well-defined excitation band at 316nm. Significantly, a strong light-trapping effect that decreases the incident light reflections and correspondingly increases the light absorption is unveiled through photoconductive studies for the TiO2 nanocones at 0.04M having a surface area of 81.767 m2/g. The investigation essentially suggests that the as-prepared one-dimensional nanostructures would serve as efficient photoanodes in environment safe third-generation solar cells.

Effect of temperature in formation of nanocrystal on chemically deposited (Cd-Zn) S: CdCl2; La, Eu films

Results of Photoconductivity (PC) and Photovoltaic (PV) studies for (Cd-Zn)S: CdCl2;La,Eu films presented in different temperature of depositions along with Thiophenol (TP) and Poly Vinyl Chloride (PVC) using as a capping agent. Films have been characterized using Photoconductivity excitation spectra, optical absorption, Photoluminescence (PL), X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The band gap of such films is evaluated by Photoconductivity excitation spectra and optical absorption. The direct optical band gap of such films was found in the range 2.74-3.04 eV for different deposition temperature. These changing of band gap suggesting the quantum confinement effect in the developed nanoscale size of the particles. The PL spectra of both films nanoparticles showed emission peaks at 436nm, 461nm, 480nm, 504nm and 536nm respectively. SEM micrograph shows the morphological structure and better growth conduction in presence of capping agent at low temperature deposition. Results of XRD studies are associated to different prominent lines of CdS and ZnS. Both studies represent average particle sizes of the order 5.49 – 9.125Å.

Synthesis, crystal growth and characterization of piperazinium 5-nitrosalicylate (P5NS) single crystal for nonlinear optical (NLO) applications

A single crystal of Piperazinium 5-nitrosalicylate (P5NS) was grown by using slow evaporation solution technique (SEST). The structural analysis (crystal system & cell parameter) of the grown P5NS crystal was examined by single crystal XRD and it exposed that the P5NS crystal has a crystal triclinic system and space group (P-1). Using powder XRD analysis, miller index and (h k l) planes were identified. The P5NS crystal has a sharp cutoff wavelength around 380 nm and is transparent in UV region. The FTIR analysis was investigated on the P5NS crystal to find out the P5NS functional groups. The thermogravimetric and differential thermal analysis illustrate that the P5NS crystal is thermally stable upto 255 °C. Further increase in the temperature resulted in decomposition of P5NS. The etch pit density of P5NS crystal has been calculated by using the chemical etching analysis. The Photoconductivity study reveals that the grown PMC crystal has positive photoconductive nature. The electrical properties, dielectric constant and dielectric loss were determined. The laser damage threshold (LDT) analysis was investigated by Nd: YAG laser and the wavelength of laser is 1064 nm. Intermolecular interactions of P5NS is executed by the Hirshfeld surface analysis. The NLO susceptibility (χ(3)) was calculated by the Z-scan method using the source of He-Ne laser, whose wavelength is 632.8 nm.

Ecofriendly sol-gel-derived dye-sensitized solar cells with aluminium-doped tin oxide photoanode.

The manuscript reports the fabrication of an eco-friendly sol gel dye-sensitized solar cell (DSSC) based on aluminium (Al)-doped tin oxide nanoparticles with different concentrations (0.5, 1, and 5 mol%) of Al providing enhanced optical and electrical properties than its bare counterparts. The physical, chemical, optical, and electrical properties of the as-synthesized nanoparticles were studied using different analytical tools. X-ray diffraction (XRD) study reveals the crystal structure of the prepared samples ascribed to SnO2 nanoparticles uniformly with reduced crystallite size for Al-doped SnO2 nanoparticles. Field emission scanning electron microscope (FESEM) analysis reveals narrowing of particle size on doping with the Al, substantially enhancing the optical and surface characteristic features of the SnO2 nanoparticles. Photoconductivity studies indicate that all the samples have a good linear response with the increment of electric field in dark and photocurrent attributing to better photoconversion capability of the samples. Further, the optimized Al-doped SnO2 and bare SnO2 nanoparticles were subjected to sophisticated analytical studies such as high-resolution transmission electron microscope (HR-TEM) and X-ray photoelectron spectroscopy (XPS) for the better insight into their properties. The as-prepared Al-doped SnO2 nanoparticles in the present study record good optical, surface, and electrical properties which enhance their compatibility for possible photovoltaic applications especially in dye-sensitized solar cells as an environmentally safe alternate energy solution. Further, the current density-voltage (J-V) characteristics of the optimized Al-SnO2 and bare SnO2 photoanode component were probed for their suitability in DSSCs which disclosed enriched efficiency upon doping with aluminium nanoparticles.

Investigation of UV photosensor properties of Al-doped SnO2 thin films deposited by sol-gel dip-coating method

Transparent conducting aluminum doped tin oxide thin films were prepared by sol-gel dip coating method with different Al concentrations and characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), UV–Vis spectrophotometry and photoconductivity study. The variation observed in the properties of the measured films agrees with a difference in the film's thickness, which decreases when Al concentration augments. X-ray diffraction analysis reveals that all films are polycrystalline with tetragonal structure, (110) plane being the strongest diffraction peak. The crystallite size calculated by the Debye Scherrer’s formula decreases from 11.92 to 8.54 nm when Al concentration increases from 0 to 5 wt.%. AFM images showed grains uniformly distributed in the deposited films. An average transmittance greater than 80% was measured for the films and an energy gap value of about 3.9 eV was deduced from the optical analysis. Finally, the photosensitivity properties like current–voltage characteristics, I ON/I OFF ratio, growth and decay time are studied and reported. Also, we have calculated the trap depth energy using the decay portion of the rise and decay curve photocurrent.

Elucidation of a Photothermal Energy Conversion Mechanism in Hydrogenated Molybdenum Suboxide: Interplay of Trapped Charges and Their Dielectric Interactions

Hydrogenated molybdenum suboxide (HxMoO3-y) is a promising photothermal energy conversion (PEC) material. However, its charge carrier dynamics and underlying mechanisms remain unclear. Utilizing flash-photolysis time-resolved microwave conductivity, we investigated charge carrier-dielectric interactions in the Pt/HxMoO3-y composite. The charge recombination of H2-reduced Pt/HxMoO3-y was 2-3 orders of magnitude faster than that of Pt/MoO3, indicating efficient PEC. A complex photoconductivity study revealed that Pt/HxMoO3-y has two types of trapping mechanisms, Drude-Zener (DZ) and negative permittivity effect (NPE) modes, depending on the reduction temperature. Pt/HxMoO3-y reduced at 100 °C exhibited a dominant NPE owing to the electrical interaction of trapped charges with the surrounding ions and/or OH base. This polaronic trapped state retarded the PEC process. We found Pt/HxMoO3-y reduced at 200 °C to be optimal owing to the balanced suppression of the NPE and charge diffusion. This is the first report revealing the charge dynamics in hydrogenated metal oxides and their impacts on PEC processes.

Thickness dependent ultraviolet photoconductivity studies on sol-gel derived zinc oxide (ZnO) films

ZnO films of varying thicknesses (77–231 nm) were deposited using the sol-gel method for ultraviolet (UV) photodetection applications. The dependence of the photoconductivity parameters of the photodetector on the thickness of the ZnO films has been investigated for UV radiation having 365 nm wavelength and intensity of 24 µW/cm2. The deposited ZnO films exhibited poly-crystallinity with significant surface roughness (30–92 nm) and oxygen-related defects (Oi, Ozn, Vo), which were found beneficial for obtaining enhanced UV photosensitivity. The photoconducting mechanism has been studied in detail using the statistical interpretation of defects observed from the deconvolution of photoluminescence spectra. The 221 nm thick ZnO film showed improved photoconducting parameters (photoconductive gain, current responsivity, rise time and fall time) which are attributed to the increased density of all the defects under deep-level emission.

Photocarrier-induced persistent structural polarization in soft-lattice lead halide perovskites.

The success of the lead halide perovskites in diverse optoelectronics has motivated considerable interest in their fundamental photocarrier dynamics. Here we report the discovery of photocarrier-induced persistent structural polarization and local ferroelectricity in lead halide perovskites. Photoconductance studies of thin-film single-crystal CsPbBr3 at 10 K reveal long-lasting persistent photoconductance with an ultralong photocarrier lifetime beyond 106 s. X-ray diffraction studies reveal that photocarrier-induced structural polarization is present up to a critical freezing temperature. Photocapacitance studies at cryogenic temperatures further demonstrate a systematic local phase transition from linear dielectric to paraelectric and relaxor ferroelectric under increasing illumination. Our theoretical investigations highlight the critical role of photocarrier-phonon coupling and large polaron formation in driving the local relaxor ferroelectric phase transition. Our findings show that this photocarrier-induced persistent structural polarization enables the formation of ferroelectric nanodomains at low temperature, which suppress carrier recombination and offer the possibility of exploring intriguing carrier-phonon interplay and the rich polaron photophysics.

Development of Eco-Friendly TiO2 Doped ZnO Nanorods Based Dual Functional Sensor for the Sewage System Monitoring

Pertaining to the drainage of urban runoff and the expulsion of sewage, sewer systems are a vital component of urban engineering. Owing to this, a dual functional sensor to detect the toxic gases and pipeline leakages was developed with TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> doped (1, 3 and 5Wt. %) ZnO nanorods using a wet chemical approach. The morphological and structural analysis depicts the formation of nanorods morphology and characteristic ZnO hexagonal wurtzite structure (dominant (002) peak plane) despite doping. A decrease in bandgap (optical analysis −3.03 eV) and internal resistance (Nyquist plot–74 Ω) was observed when doped with 5Wt.% of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . A distinguishing p-n junction curve was observed in all the doped samples during the photoconductivity (J-V) study. A systematic experimental exploratory of the developed sensors at room temperature unfolds the improved dual functional property of the developed sensors when exposed to target gases (10 ppm) (CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> –0.60 and CO–0.64) and acceleration (2.45 V at 1 g).

Bipolar persistent photoconductivity in HgTe/CdHgTe double quantum well heterostructures and its application for reversible change in the conductivity type

We report a detailed study of the bipolar persistent photoconductivity in an HgTe/CdHgTe double quantum well (DQW), which can be a perspective for studying topological states in these structures. Photoconductivity spectra measurements in the range of 1.1–3.1 eV as well as transport measurements under different illumination conditions were performed at T = 4.2 K. Based on the results, the processes occurring in the structure under illumination and leading to a change in the carrier concentration in the DQW have been established. They include interband generation in the CdTe cap layer and in the CdHgTe barrier layer and electron transitions from the spin-split band in the CdHgTe barrier layer to the conduction band in the CdTe cap layer. The presence of the CdTe cap layer and the appropriate cadmium fraction in the CdHgTe barrier layers have been shown to be the main factors determining the key features of the spectra. Finally, we suggest an effective method of controlling the conductivity type of HgTe/CdHgTe structures using light with different wavelengths.

Tuning the photoconductivity of Co3O4 thin films by defect engineering

Light-stimulated phenomena, such as photoconductivity, allow access to the role played by structural and point defects of semiconductor oxides. We report on a systematic study of the room temperature photoconductivity of polycrystalline Co3O4 thin films grown by spray pyrolysis. Using different excitation wavelengths, we access the optical absorption edges related to Co2+ or Co3+. Structural and morphological characteristics, as well as their relation with the type of substrate, are also investigated. As-grown Co3O4 exhibits a high density of oxygen vacancies (VO), which can be modified by implementing defect engineering via annealing in different atmospheres. Regardless of the atmosphere, the XPS measurements reveal a similar drop in VO induced by thermal annealing. In addition, Co3+ ions are reduced to Co2+ on the films’ surface. The response time is tens of seconds for optical excitation above the Co3O4 absorption and increases for excitations closer to the Co2+ edge. The absence of saturation profile in as-grown Co3O4 indicates the influence of deep trap defect centers. In contrast, annealing inhibits the persistence effects of red excitations. The oxidizing atmosphere provides long response and recovery times, while annealing in Ar produces fast responses. The reduction in Vo on the film surfaces indicates that oxygen vacancies are not responsible for the deep traps.

Analysis of various properties of l-alaninium p-toluenesulfonate single crystal for nonlinear optical applications

L-alaninium p-toluenesulfonate single crystal is a promising organic nonlinear optical material for second harmonic generation (SHG) and optical limiting applications. In this work, the slow evaporation solution growth technique was employed to grow a good quality single crystal at ambient conditions. The obtained crystal’s structure, unit cell dimensions and phase identification were done by Powder X-ray diffraction (PXRD) and found that it crystallizes in orthorhombic structure with space group P212121 and exhibits non-centrosymmetric nature. Its crystalline purity was characterized by High-Resolution X-ray diffraction (HRXRD) and found highly crystalline with minor grain boundaries. The Hirschfield surface analysis was carried out to identify major interactions. The photopyroelectric (PPE) technique was employed to determine the specific heat capacity (Cp) and thermal conductivity (k) of the grown sample. A low value of inhomogeneity in the birefringence of the titled crystal suggests its better optical quality. Photo-conductivity studies inferred that the titled compound features negative photoconductivity and the currents produced were in nanoscale. Further, the Piezoelectric coefficient (d33) was also measured. The mechanical strength was studied by giving shock waves to the crystals in terms of shock damage threshold (SDT) and by giving static indentations to the crystals in Vickers’s microhardness test. The third-order nonlinear optical properties were studied by Z-scan analysis.