Experimental investigation on the structural,dielectric, ferroelectric and piezoelectric properties of La doped ZnO nanoparticles and their application in dye-sensitized solar cells

Pure and lanthanum (La) doped ZnO nanorods were synthesized via co-precipitation method. The structure and morphology of as grown ZnO and La-ZnO nanoparticles were studied using transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) methods. The values of remnant polarization and coercive field were found to be 0.027 μC/cm² and 1.33 kV/cm, respectively, for as grown La-ZnO nanostructures. High Curie temperature (276 °C) for doped ZnO was observed in dielectric study. Piezoelectric coefficient at room temperature was found to be 101.30 pm/V. I-V characteristics were studied for both pure and doped ZnO nanoparticles. Photo-anodes of dye-sensitized solar cells (DSSCs) were made using ZnO and La-ZnO nanorods. The conversion efficiency and short circuit current density of La-ZnO nanorods based DSSC were 0.36% and 1.31 mA/cm², respectively, which were found to be largely enhanced when compared with that of pure ZnO based DSSC (0.20% and 0.94 mA/cm²).     

Utilization of surface plasmon resonance of Au/Pt nanoparticles for highly photosensitive ZnO nanorods network based plasmon field effect transistor

Hydrothermally processed highly photosensitive ZnO nanorods based plasmon field effect transistors (PFETs) have been demonstrated utilizing the surface plasmon resonance coupling of Au and Pt nanoparticles at Au/Pt and ZnO interface. A significantly enhanced photocurrent was observed due to the plasmonic effect of the metal nanoparticles (NPs). The Pt coated PFETs showed I_on/I_off ratio more than 3 × 10⁴ under the dark condition, with field-effect mobility of 26 cm² V⁻¹ s⁻¹ and threshold voltage of −2.7 V. Moreover, under the illumination of UV light (λ = 350 nm) the PFET revealed photocurrent gain of 10⁵ under off-state (−5 V) of operation. Additionally, the electrical performance of PFETs was investigated in detail on the basis of charge transfer at metal/ZnO interface. The ZnO nanorods growth temperature was preserved at 110 °C which allowed a low temperature, economical and simple method to develop highly photosensitive ZnO nanorods network based PFETs for large scale production.     

Plasmon-enhanced luminescence of Sm complex using silver nanoparticles in Polyvinyl Alcohol

Silver (Ag) nanoparticles (NPs) were prepared by laser ablation in water with an aim to enhance the luminescence of rare earth coordinated complex in polymer host. A fixed concentration of the complex containing Samarium (Sm), Salicylic acid (Sal) and 1, 10-phenanthroline (Phen) were combined with different concentrations of silver NPs in PolyVinyl Alcohol at room temperature. Absorption spectrum and XRD patterns of the sample show that the Sm(Sal)₃Phen complex is accompanied by Ag NPs. The luminescence from the complex was recorded in the presence and absence of Ag NPs using two different excitation wavelengths viz. 400 and 355 nm. Of these, 400 nm radiation falls in the surface plasmon resonance of Ag NPs. It was found that the Ag NPs led to a significant enhancement in luminescence of the complex. Surprisingly, a high concentration of Ag NPs tends to quench the luminescence.     

Enhanced UV-excited luminescence of europium ions in silver/tin-doped glass

Glasses containing silver, tin and europium were prepared by the melt-quenching technique with silver nanoparticles (NPs) being embedded upon heat treatment (HT). An intensification of Eu³⁺ ions emission was observed for non-resonant excitation around 270 nm, corresponding to UV absorption in the material. Optical measurements suggest that light absorption occurs at single Ag⁺ ions and/or twofold-coordinated Sn centers followed by energy transfer to europium which results in populating the ⁵D₀ emitting state in Eu³⁺. After HT at 843 K, a quenching effect is observed on Eu³⁺ luminescence with increasing holding time in the 350–550 nm excitation range. The quenching effect shows with the presence of Ag NPs which may provide multipole radiationless pathways for excitation energy loss in europium ions.     

Enhanced power efficiency of ZnO based organic/inorganic solar cells by surface modification

We present series of strategies to enhance efficiency of ZnO nanorods based organic/inorganic solar cells with spin-coated P3HT:PCBM blend as active layer. The performance of the as-fabricated devices is improved by controlling the size of ZnO nanorods, annealing temperature and time of active layer, surface modification of ZnO with PSBTBT. Optimized device of ITO/ZnO nanorod/P3HT:PCBM/Ag device with PSBTBT surface modification and air exposure reaches an efficiency of 2.02% with a short-circuit current density, open-circuit voltage and fill factor of 13.23 mA cm⁻², 0.547 V and 28%, respectively, under AM 1.5 irradiation of 100 mW m⁻², the increase in efficiency is 7-fold of the PSBTBT surface modified ITO/ZnO nanorods/P3HT:PCBM/Ag device compared with the unmodified one, which is own to the increased interface contact, expanded light absorption, tailored band alignment attributed to PSBTBT. We found exposure to air and surface modification is crucial to improve the device performance, and we discussed the mechanisms that affect the performance of the devices in detail.     

AZO/Ag/AZO multilayer films prepared by DC magnetron sputtering for dye-sensitized solar cell application

Ag films were deposited on Al-doped ZnO (AZO) films and coated with AZO to fabricate AZO/Ag/AZO multilayer films by DC magnetron sputtering on glass substrates without heating of glass substrates. The best multilayer films have low sheet resistance of 19.8 Ω/Sq and average transmittance values of 61% in visible region. It was found that the highest figure of merit (F_TC) is 6.9 × 10⁻⁴ Ω⁻¹. For the dye-sensitized solar cell (DSSC) application, the multilayer films were used as transparent conductive electrode (multilayer films/ZnO + Eosin-Y/LiI + I₂/Pt/FTO). The best DSSC based on the multilayer films showed that open circuit voltage (V_oc) of 0.47 V, short circuit current density (J_sc) of 2.24 mA/cm², fill factor (FF) of 0.58 and incident photon-to-current conversion efficiency (η) of 0.61%. It was shown that the AZO/Ag/AZO multilayer films have potential for application in DSSC.     

Enhanced performance of bi-layer Nb2O5 coated TiO2 nanoparticles/nanowires composite photoanode in dye-sensitized solar cells

Dye sensitized solar cells (DSSCs) were fabricated based on coumarin NKX-2700 dye sensitized bi-layer photoanode and quasi-solid state electrolyte sandwiched together with cobalt sulfide coated counter electrode. A novel bi-layer photoanode has been prepared using composite mixtures of 90 wt.% TiO₂ nanoparticles + 10 wt.% TiO₂ nanowires (TNPWs) as active layer and Nb₂O₅ is coated on the active layer, which acts as scattering layer. Hafnium oxide (HfO₂) was applied over the TNPWs/Nb₂O₅ photoanode film, as a blocking layer. TiO₂ nanoparticles (TNPs), TiO₂ nanowires (TNWs) and TNPWs/Nb₂O₅ were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The sensitizing organic dye coumarin NKX-2700 displayed maximum absorption wavelength (λ_max) at 525 nm, which could be observed from the UV–vis spectrum. DSSC-1 fabricated with composite bi-layer photoanode revealed enhanced photo-current efficiency (PCE) as compared to other DSSCs and illustrated photovoltaic parameters; short-circuit current J_SC = 18 mA/cm², open circuit voltage (V_OC) = 700 mV, fill factor (FF) = 64% and PCE (η) = 8.06%. The electron transport and charge recombination behaviors of DSSCs were investigated by electrochemical impedance spectra (EIS) and the results illustrated that the DSSC-1 showed the lowest charge transport resistance (R_tr) and the longest electron lifetime (τ_eff). Therefore, in the present investigation, it could be concluded that the novel bi-layer photoanode with blocking layer increased the short circuit current, electron transport and suppressed the recombination of charge carriers at the photoanode/dye/electrolyte interface in DSSC-1.     

Targeted sonocatalytic cancer cell injury using avidin-conjugated titanium dioxide nanoparticles

In this study, we applied sonodynamic therapy to cancer cells based on the delivery of titanium dioxide (TiO₂) nanoparticles (NPs) modified with avidin protein, which preferentially discriminated cancerous cells from healthy cells. Subsequently, hydroxyl radicals were generated from the TiO₂ NPs after activation by external ultrasound irradiation (TiO₂/US treatment). Although 30% of the normal breast cells (human mammary epithelial cells) exhibited the uptake of avidin-modified TiO₂ NPs, over 80% of the breast cancer cells (MCF-7) exhibited the uptake of avidin-TiO₂ NPs. Next the effect of the TiO₂/US treatment on MCF-7 cell growth was examined for up to 96 h after 1-MHz ultrasound was applied (0.1 W/cm², 30 s) to cells that incorporated the TiO₂ NPs. No apparent cell injury was observed until 24 h after the treatment, but the viable cell concentration declined to 68% compared with the control at 96 h.     

A miniaturized prototype of resonant banana-shaped photoacoustic cell for gas sensing

A resonant photoacoustic cell intended for laser-spectroscopy gas sensing is represented. This cell is a miniature imitation of a macro-scale banana-shaped cell developed previously. The parameters, which specify the cavity shape, are chosen so as not only to provide optimal cell operation at a selected acoustic resonance but also to reduce substantially the cell sizes. A miniaturized prototype cell (the volume of acoustic cavity of ∼5 mm³) adapted to the narrow diffraction-limited beam of near-infrared laser is produced and examined experimentally. The noise-associated measurement error and laser-initiated signals are studied as functions of modulation frequency. The background signal and the useful response to light absorption by the gas are analyzed in measurements of absorption for ammonia in nitrogen flow with the help of a pigtailed DFB laser diode oscillated near a wavelength of 1.53 μm. The performance of prototype operation at the second longitudinal acoustic resonance (the resonance frequency of ∼32.9 kHz, Q-factor of ∼16.3) is estimated. The noise-limited minimal detectable absorption normalized to laser-beam power and detection bandwidth is ∼8.07 × 10⁻⁸ cm⁻¹ W Hz^−1/2. The amplitude of the background signal is equivalent to an absorption coefficient of ∼2.51 × 10⁻⁵ cm⁻¹. Advantages and drawbacks of the cell prototype are discussed. Despite low absorption-sensing performance, the produced miniaturized cell prototype shows a good capability of gas-leak detection.     

Enhanced OH radical generation by dual-frequency ultrasound with TiO2 nanoparticles: Its application to targeted sonodynamic therapy

The present study demonstrated the enhanced hydroxyl (OH) radical generation by combined use of dual-frequency (0.5 MHz and 1 MHz) ultrasound (US) and titanium dioxide (TiO₂) nanoparticles (NPs) as sonocatalyst. The OH radical generation became the maximum, when 0.5 MHz US was irradiated at an intensity of 0.8 W/cm² and 1 MHz US was irradiated at intensities at 0.4 W/cm² in the presence of TiO₂ NPs under the examined conditions. After incorporation of TiO₂ NPs modified with targeting protein pre-S1/S2, HepG2 cancer cells were subjected to the dual-frequency US at optimum irradiation intensities (“targeted-TiO₂/dual-US treatment”). Growth of the HepG2 cells was reduced by 46% compared with the control condition after irradiation of dual-frequency US for 60 s with TiO₂ NPs incorporation. In contrast, HepG2 cell growth was almost the same as that in the control condition when cells were irradiated with either 0.5 MHz or 1 MHz ultrasound alone without TiO₂ NP incorporation.     

Diffraction patterns and nonlinear optical properties of gold nanoparticles

Stable gold nanoparticles have been prepared by using soluble starch as both the reducing and stabilizing agents; this reaction was carried out at 40 °C for 5 h. The obtained gold nanoparticles were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy (TEM) and z-scan technique. The size of these nanoparticles was found to be in the range of 12–22 nm as analyzed using transmission electron micrographs. The optical properties of gold nanoparticles have been measured showing the surface plasmon resonance. The second-order nonlinear optical (NLO) properties were investigated by using a continuous-wave (CW) He–Ne laser beam with a wavelength of 632.8 nm at three different incident intensities by means of single beam techniques. The nonlinear refractive indices of gold nanoparticles were obtained from close aperture z-scan in order of 10^?7 cm²/W. Then, they were compared with diffraction patterns observed in far-field. The nonlinear absorption of these nanoparticles was obtained from open aperture z-scan technique. The values of nonlinear absorption coefficient are obtained in order of 10^?1 cm/W.     

Fabrication and characteristics of photodiode based on ZnO nanowire arrays and spray-coated regioregular P3HT layers

A photodiode based on well-aligned ZnO nanowire arrays (ZNAs) and spray-coated regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) layers hybrid hetero junctions was fabricated, and its electrical characteristics in dark and under illumination with a solar simulator were investigated. Current–voltage (I–V) data of ITO/ZNAs/P3HT/Ag device in dark and under illumination showed typical diode characteristics. A rectification ratio (RR) of 22.7 at 1.7 V and a low turn-on voltage of 0.4 V in dark were obtained. Also, the photodiode with high photo-response in the order of 0.31 A/W at -2 V using 80 mW/cm² illumination power was observed. Upon increasing illumination power from 40 to 100 mW/cm², the RR value for the photodiode continuously was improved with a highest value of 12.5.     

Nanocomposite materials based on poly(vinyl chloride) and bovine serum albumin modified ZnO through ultrasonic irradiation as a green technique: Optical,thermal, mechanical and morphological properties

In this project, physicochemical properties of poly(vinyl chloride) (PVC) reinforced by ZnO nanoparticles (NPs) were studied. Firstly, ZnO NPs were modified with bovine serum albumin (BSA) as an organo-modifier and biocompatible substance through ultrasound irradiation as environmental friendly, low cost and rapid means. Nanocomposite (NC) films were prepared by loadings of various ratios of ZnO/BSA NPs (3, 6 and 9 wt%) inside the PVC. Structural morphology and physical properties of the ZnO-BSA NPs and NC films were investigated via Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis (TGA), transmission electron microscopy and field emission scanning electron microscopy. According to the obtained information from the TGA, an increase in the thermal stability can be clearly observed. Also the results of contact angle analysis indicated with increasing percent of ZnO/BSA NPs into PVC the hydrophilic behaviors of NCs were increased.     

The effect of Ag layer thickness on the properties of WO3/Ag/MoO3 multilayer films as anode in organic light emitting diodes

Transparent conductive WO₃/Ag/MoO₃ (WAM) multilayer electrodes were fabricated by thermal evaporation and the effects of Ag layer thickness on the optoelectronic and structural properties of multilayer electrode as anode in organic light emitting diodes (OLEDs) were investigated using different analytical methods. For Ag layers with thickness varying between 5 and 20 nm, the best WAM performances, high optical transmittance (81.7%, at around 550 nm), and low electrical sheet resistance (9.75 Ω/cm²) were obtained for 15 nm thickness. Also, the WAM structure with 15 nm of Ag layer thickness has a very smooth surface with an RMS roughness of 0.37 nm, which is suitable for use as transparent conductive anode in OLEDs. The current density?voltage?luminance (J?V?L) characteristics measurement shows that the current density of WAM/PEDOT:PSS/TPD/Alq₃/LiF/Al organic diode increases with the increase in thickness of Ag and WO₃/Ag (15 nm)/MoO₃ device exhibits a higher luminance intensity at lower voltage than ITO/PEDOT:PSS/TPD/Alq₃/LiF/Al control device. Furthermore, this device shows the highest power efficiency (0.31 lm/W) and current efficiency (1.2 cd/A) at the current density of 20 mA/cm², which is improved 58% and 41% compared with those of the ITO-based device, respectively. The lifetime of the WO₃/Ag (15 nm)/MoO₃ device was measured to be 50 h at an initial luminance of 50 cd/m², which is five times longer than 10 h for ITO-based device.     

Controlled repeated chemical growth of ZnO films for dye-sensitized solar cells

The controlled growth of ZnO nanorods perpendicular to substrate surface i.e. c-axis by a repeated chemical deposition method for efficient dye-sensitized solar cell application is described. X-ray diffraction study shows the wurtzite structure of ZnO with high crystallinity. Intensity and newly evolved peaks of the ZnO are found to be thickness dependent. Dye loving flower-like globular architecture of ZnO is observed after 8 μm thickness. Dye-sensitized solar cell studies show the solar-to-electrical conversion efficiency of 2.21% for 11 μm ZnO electrode when illuminated with 80 mW/cm².     

Investigation of reduced graphene oxide effects on ultra-violet detection of ZnO thin film

The reduced graphene oxide (rGO) incorporated ZnO thin films were fabricated by dip-coating method. The Raman and FT-IR spectra of 0.075 wt% incorporated composite film showed reduction of GO in composite film. The transmittanceProd. Type: FTP spectra have shown that rGO incorporation increase the visible light absorption of ZnO thin film while the calculated band gaps of samples were decreased from 3.28 to 3.25 eV by increasing the rGO content. The linear trend of I–V curve suggests an ohmic contact between ZnO and rGO. Besides, it was found that by increasing the rGO content, the electrical resistivity was decreased from 4.32×10² Ω cm for pure ZnO film to 2.4×10¹ Ω cm for 0.225 wt% rGO incorporated composite film. The composite photodetectors not only possessed a desirable UV photosensitivity, but also the response time of optimum sample containing 0.075 wt% rGO was reduced to about one-half of pure ZnO thin film. Also, the calculated signal to noise (SNR) showed that highly conductive rGO in composite thin films facilitate the carrier transportation by removing the trapping centers. The mechanism of photoresponsivity improvement of composite thin films was proposed by carrier transportation process.     

ZnO/ZrO2 nanocomposite: Sonosynthesis,characterization and its application for wastewater treatment

ZnO/ZrO₂ nanocomposites with different ZnO: ZrO₂ molar ratios (2:1, 1:1, and 1:2)were prepared by sol gel approach under ultrasonic irradiation. For preparation of the nano-composites, the ZnO gel was directly incorporated into the ZrO₂ gel at different molar ratios. The reaction mixture was stirred continuously for two days and then it was ultrasonoicated for 30 min. The filtrated composite gel was washed, and then calcinated at 300 °C in furnace for 3 h. X-ray powder diffraction patterns exhibited well-formed crystal structures and pure crystalline phases in the synthesized nanoparticles (NPs). The FT-IR analyses indicated that the positions of peaks related to Zn-O and Zr-O absorption bands did not change in nano-composites. In addition, FESEM images indicated uniform spherical morphology of the NPs. The highest photo-degradation performance of Congo red (as a model water pollutant) was obtained by 1:2molar ratio of ZrO₂: ZnO in the nano-composite. The particle size and band gap were considered as important factors on nano-catalysts performance. Furthermore, the effects of ultrasonic irradiation, pH, and the concentration of pollutant in solution were investigated on photocatalytic performance of optimum nanocomposite.     

Ultrasonic-assisted degradation of phenazopyridine with a combination of Sm-doped ZnO nanoparticles and inorganic oxidants

Pure and samarium doped ZnO nanoparticles were synthesized by a sonochemical method and characterized by TEM, SEM, EDX, XRD, Pl, and DRS techniques. The average crystallite size of pure and Sm-doped ZnO nanoparticles was about 20 nm. The sonocatalytic activity of pure and Sm-doped ZnO nanoparticles was considered toward degradation of phenazopyridine as a model organic contaminant. The Sm-doped ZnO nanoparticles with Sm concentration of 0.4 mol% indicated a higher sonocatalytic activity (59%) than the pure ZnO (51%) and other Sm-doped ZnO nanoparticles. It was believed that Sm³⁺ ion with optimal concentration (0.4 mol%) can act as superficial trapping for electrons in the conduction band of ZnO and delayed the recombination of charge carriers. The influence of the nature and concentration of various oxidants, including periodate, hydrogen peroxide, peroxymonosulfate, and peroxydisulfate on the sonocatalytic activity of Sm-doped ZnO nanoparticles was studied. The influence of the oxidants concentration (0.2–1.4 g L⁻¹) on the degradation rate was established by the 3D response surface and the 2D contour plots. The results demonstrated that the utilizing of oxidants in combination with Sm-doped ZnO resulting in rapid removal of contaminant, which can be referable to a dual role of oxidants; (i) scavenging the generated electrons in the conduction band of ZnO and (ii) creating highly reactive radical species under ultrasonic irradiation. It was found that the Sm-doped ZnO and periodate combination is the most efficient catalytic system under ultrasonic irradiation.     

Green synthesis of silver-graphene nanocomposite-based transparent conducting film

In the present work, silver nanoparticles (Ag NPs)/graphene nanocomposite has been synthesized successfully by simple solvothermal method via green route. Citric acid is used as green reducing agent for the reduction of graphene oxide (GO) and Ag ions. Silver nitrate is used as a precursor material for Ag NPs. As synthesized Ag NPs/graphene nanocomposite has been characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infra-red spectroscopy, UV–vis spectroscopy, thermal gravimetric analysis, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. Experimental results confirm the reduction of GO and the successful formation of Ag NPs decorated graphene nanosheets. In addition, spray coating technique is employed for the fabrication of transparent conducting films. Enhancement in the optoelectrical signatures has been achieved using thermal graphitization of fabricated films. Thermal graphitization at 800 °C for 1 h marks the best performance of fabricated film with sheet resistance of ~3.4 kΩ/□ and transmittance (550 nm) of ~66.40%, respectively.     

Enhanced infrared to visible upconversion emission in Er3+ doped phosphate glass: Role of silver nanoparticles

Phosphate glasses with compositions (59.5–x)P₂O₅–MgO–xAgCl–0.5Er₂O₃ (0.0≤x≤1.5 mol%) containing fixed concentration of Er³⁺ ion with and without silver nanoparticles (NPs) are prepared using melt quenching technique. The amorphous nature of the glass is confirmed using the X-ray diffraction method. The homogeneous distribution of spherical Ag NPs (average size ～37 nm) in the glassy matrix is evidenced from the transmission electron microscopy (TEM) analyses. The UV–vis–NIR absorption spectra shows 10 bands corresponding to ⁴I_13/2, ⁴I_11/2, ⁴I_9/2, ⁴F_9/2, ⁴S_3/2, ²H_11/2, ⁴F_7/2, ⁴F_5/2, ²G_9/2, ⁴G_11/2 transitions in which the most intense bands are ²H_11/2 and ⁴G_11/2. The absorption spectrum of Er³⁺ ions free glass sample containing Ag NPs displays a prominent surface Plasmon resonance (SPR) band located at 528 nm. The infrared to visible frequency upconversion (UC) emission under 797 nm excitation shows two emission bands green (⁴S_3/2–⁴I_15/2) and red (⁴F_9/2–⁴I_15/2) centered at 540 nm and 634 nm, respectively, corresponding to Er³⁺ transitions. An enhancement in UC emission intensity of green band (⁴S_3/2–⁴I_15/2) is observed in the presence of silver NPs and the maximum enhancement occurred for 1.5 mol% AgCl. However, the enhancement of emission intensity of the red band (⁴F_9/2–⁴I_15/2) is smaller. The enhancement of UC emission is understood in terms of the intensified local field effect due to silver NPs.