Nonlinear Optical Properties Of ZnO Research Articles

Chemical Bath Deposition Grown Zno Thin Films: Role of Manganese Doping

In this study, the effect of Mn doping concentration on the structural, microstructural, linear and nonlinear optical properties of ZnO was investigated. Pristine and Mn-doped ZnO films were prepared by chemical bath deposition on a glass substrate. The crystal structure and surface morphology of the films were determined by X-ray diffraction and force electron scanning microscopy (FESEM). X-Ray Diffraction (XRD) analysis revealed that the films had a polycrystalline structure and all films were ZnO with a hexagonal structure. In addition, a shift was detected in the XRD pattern of the films with the Mn doping process. According to the FESEM results, the surface of the films has irregularly shaped particles. Linear and nonlinear optical parameters were estimated using transmittance and absorbance measurements. And then, optical absorption coefficient, extinction coefficient, refractive index, optical dielectric constants, surface, and volume energy loss functions, optical band gap values, and optical and electrical conductivity were determined as linear optical properties. It was determined that these properties were affected by Mn-doped ratios. It was determined that nonlinear optical properties such as linear optical properties were also affected by the doping process.

Nonlinear Optical Properties of ZnO variants

Investigation on nonlinear optical properties of ZnO with Au-Ag NPs was done in this report using a femtosecond laser with a wavelength of 720 nm using Z-scan measurement. ZnO sample was prepared by a two- step process: seeding process via ultrasonic spray pyrolysis and growth process via hydrothermal methods, while ZnO with Au-Ag NPs was done by chemical reduction. ZnO shown saturable absorbance properties with nonlinear absorption coefficient, β = 1.63×10−6 cm/W, while ZnO deposited with Au-Ag NPs, shows reverse saturable absorption properties, for which ZnO Au NPs have the highest value of 5.60×10−6 cm/W, nonlinear refractive index response for pristine ZnO gave self- focusing effect with the value of a nonlinear refractive index, γ = 2.29×10−12 cm2/W. In contrast, the rest of ZnO with Au-Ag NPs gave the self- defocusing effect, with the Au NPs having the lowest response with γ = −5.79×10−12 cm2/W. This gives ZnO Au NPs have the highest third-order nonlinear susceptibility, χ(3) = 14.62×10−10 esu, which is an enhancement from pristine ZnO.

Investigation of third order nonlinear optical properties of undoped and indium doped zinc oxide (InZnO) thin films by nanosecond Z-scan technique

We report the investigation of third order nonlinear optical properties of undoped zinc oxide and indium doped zinc oxide thin films using nanosecond (6ns, 18μJ at 532nm) Z-scan technique. Undoped (ZnO) and indium doped zinc oxide (InZnO) thin films were synthesized on quart silica substrate by using radio frequency (RF) magnetron sputtering technique. The structural and characterization of deposited thin films were analyzed by X-ray diffraction (XRD). In XRD results show different behaviors as amorphous oxide semiconductor and polycrystalline oxide semiconductor for ZnO and InZnO thin films respectively. Elemental compositions of thin films were analyzed by energy dispersive spectrometer (EDS). Surface morphology of ZnO and InZnO films were measured by using scanning electron microscopy (SEM), which show uniform and regular surface with small grain size distribution. Linear optical transmission and reflection thin films were analyzed by UV–VIS spectrometer. The UV–VIS results reveal that the optical transmittances of deposited thin films were increased after doping indium. The third order nonlinear optical properties of ZnO and InZnO thin films were carried out using nanosecond (6ns) laser Z-scan technique at 532nm wavelength. In open aperture case, both ZnO and InZnO thin films are show reverse saturable absorption (RSA) behaviors. For close-aperture Z-scan, the transmittance curve of ZnO thin film occurs as valley-peak (positive nonlinear refraction) characteristic, which indicates self-focusing behavior.

Defect engineering in ZnO nanocones for visible photoconductivity and nonlinear absorption.

Nanostructured ZnO is a promising material for optoelectronic and nonlinear optical applications because of the flexibility of band gap engineering by means of various defect states present in it. Employing the time-correlated single photon counting photoluminescence technique, the correlation between defect levels and optoelectronic and nonlinear optical properties of ZnO is explored in this work. By a facile solution method, ZnO nanocones with a dominating preferential orientation along energetically less favorable, oxygen terminated (10̄11) facets were synthesized using a passivating capping agent. Photoluminescence spectra demonstrate that the as-grown samples have both oxygen and zinc vacancies, and after calcination in air oxygen vacancies vanish, but zinc vacancies are enhanced. Photoconductivity of the samples reduces significantly upon calcination, confirming the reduction in oxygen vacancies. However, the samples exhibit a significant enhancement in the nonlinear optical absorption coefficient upon calcination, indicating that the effective two-photon absorption causing the nonlinear optical behaviour originates from zinc vacancies. These results illustrate the vast possibilities of band gap engineering in intrinsic ZnO for future optoelectronic applications.

Ensemble and Individual Characterization of the Nonlinear Optical Properties of ZnO and BaTiO3 Nanocrystals

Hyper Rayleigh scattering (HRS) and second harmonic (SH) microscopy were used to study the second order nonlinear optical response of ZnO and BaTiO3 nanocrystals, which have been recently proposed as new markers for bioimaging. HRS, combined with dynamic light scattering, was first used to retrieve hyperpolarizabilities and nonlinear coefficients of both type of nanocrystals. The results indicate that the main contribution to the SH signal is related to the bulk noncentrosymmetric structure of the particles. Successively, we carried out the inspection of individual nanocrystals by SH microscopy, interpreting their response using the nonlinear coefficients deduced from HRS.

Nonlinear Optical Properties of ZnO

(a) Photoluminescence spectrum of the ZnO powders ob-tained with a He-Cd laser (325 nm). Inset shows the transmission electron microscopy (TEM) image of the ZnO powders used for the measurements. (b) Emission spectrum of the ZnO powders obtained by intensive excitation of fundamentals, such as 800, 750, and 710 nm. The dotted line indicates the band gap of ZnO. (c) Refractive index and its difference related term as a function of the wavelength.

Strain-Induced Modulations of Electro-Optic and Nonlinear Optical Properties of ZnO: A First-Principles Study

Strain-dependent electro-optic constant r33 and nonlinear optical coefficient d33 of ZnO are investigated systematically using density-functional theory based linear-response perturbation method. Miscellaneous properties, such as dielectric constants, elastic constants, piezoelectric coefficients, nonlinear optical coefficients, and electro-optic constants of other II-VI compound semiconductors (both Wurtzite and Zinc-blende structures) are also calculated for comparison with the results of unstrained ZnO. Extensive first-principles calculations show that both r33 and d33 of ZnO decrease almost linearly with increasing strains, which indicates that appropriate compression along the [0001] direction of ZnO could enhance its electro-optic and nonlinear optical properties, while stretching may weaken the corresponding properties. Among the involved Wurtzite structures, ZnO has the highest elastic constant, piezoelectric coefficient and electro-optic constant, showing practical importance.

Enhanced luminescence and nonlinear optical properties of nanocomposites of ZnO–Cu

In this article, we present the spectral and nonlinear optical properties of ZnO–Cu nanocomposites prepared by colloidal chemical synthesis. The emission consisted of two peaks. The 385-nm ultraviolet (UV) peak is attributed to ZnO and the 550-nm visible peak is attributed to Cu nanocolloids. Obvious enhancement of UV and visible emission of the samples is observed and the strongest UV emission of a typical ZnO–Cu nanocomposite is over three times stronger than that of pure ZnO. Cu acts as a sensitizer and the enhancement of UV emission are caused by excitons formed at the interface between Cu and ZnO. As the volume fraction of Cu increases beyond a particular value, the intensity of the UV peak decreases while the intensity of the visible peak increases, and the strongest visible emission of a typical ZnO–Cu nanocomposite is over ten times stronger than that of pure Cu. The emission mechanism is discussed. Nonlinear optical response of these samples is studied using nanosecond laser pulses from a tunable laser in the wavelength range of 450–650 nm, which includes the surface plasmon absorption (SPA) band. The nonlinear response is wavelength dependent and switching from reverse saturable absorption (RSA) to saturable absorption (SA) has been observed for Cu nanocolloids as the excitation wavelength changes from the low absorption window region to higher absorption regime near the SPA band. However, ZnO colloids and ZnO–Cu nanocomposites exhibit induced absorption at this wavelength. Such a changeover in the sign of the nonlinearity of ZnO–Cu nanocomposites, with respect to Cu nanocolloids, is related to the interplay of plasmon band bleach and optical limiting mechanisms. The SA again changes back to RSA when we move over to the infrared region. The ZnO–Cu nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behavior. The nonlinear refractive index and the nonlinear absorption increases with increasing Cu volume fraction at 532 nm. The observed nonlinear absorption is explained through two-photon absorption followed by weak free-carrier absorption and interband absorption mechanisms. This study is important in identifying the spectral range and composition over which the nonlinear material acts as a RSA-based optical limiter. ZnO–Cu is a potential nanocomposite material for the light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.