Enhancement of nonlinear optical susceptibility of CuPc films by ITO layer

In the present study, the Copper Phthalocyanine (CuPc)/ITO thin film was fabricated using thermal evaporation method. The structural property was analyzed by X-ray diffraction study and confirms that the thin film has been preferentially grown along (200) plane. The atomic force microscope study was carried out on deposited film and quality of thin films is assessed by calculating the roughness of the films. The direct and indirect band gap, linear and nonlinear optical characteristics of grown films were calculated by using UV–Vis–NIR spectrometer studies. The calculated values of the first direct and indirect band gaps (E_g1(d) & E_g1(ind)) are 1.879 and 1.644 eV as a fundamental gap, while the values of second direct and indirect band gap (E_g2(d) & E_g2(ind)) are 1.660 and 1.498 eV as an onset gap for CuPc. The values of nonlinear refractive index (n₂) and third order nonlinear optical susceptibility (χ³) are found to be 5 × 10⁻⁸ and 8 × 10⁻⁹ (theoretical) and 5.2 × 10⁻⁸ and 1.56 × 10⁻⁷ (experimental) respectively. The optical band and third order nonlinear properties suggest that the as-prepared films are may be applied in optoelectronic and nonlinear applications.     

Low temperature phase barium borate: A new optical limiter in continuous wave and nano pulsed regime

Low temperature phase barium borate was synthesized by hydrothermal method. XRD analysis confirms the formation of γ-BBO or hydrated barium polyborate (Ba₃B₆O₉(OH)₆) which crystallizes in monoclinic system in the P2/c space group. The molecular structure analysis shows the presence of dominant BO₄ unit and the hydrated nature of material. γ-BBO exhibits sharp absorption edge at 202 nm and highly transparency in the UV–Visible–NIR region. The peak at 347 nm in the emission spectrum is due to the presence of self-trapped exciton. The third order nonlinear optical properties and limiting behavior of low temperature barium borate in both pulsed and continuous wave regime were studied. The effective 2PA absorption coefficient of γ-BBO under ns pulse excitation is estimated to be 0.38 × 10⁻¹⁰ m/W. The nonlinear absorption coefficient, refractive index and optical susceptibility of the material in cw regime were found to be in the order of 10⁻⁵ m W⁻¹, 10⁻¹² m² W⁻¹, 10⁻⁶ esu respectively. In both regimes, low temperature phase barium borate exhibits better optical limiting properties than high temperature phase β-BBO.     

Influence of electron beam irradiation on nonlinear optical properties of Al doped ZnO thin films for optoelectronic device applications in the cw laser regime

We present the studies on third-order nonlinear optical properties of Al doped ZnO thin films irradiated with electron beam at different dose rate. Al doped ZnO thin films were deposited on a glass substrate by spray pyrolysis deposition technique. The thin films were irradiated using the 8 MeV electron beam from microtron ranging from 1  kG y to 5  kG y. Nonlinear optical studies were carried out by employing the single beam Z-scan technique to determine the sign and magnitude of absorptive and refractive nonlinearities of the irradiated thin films. Continuous wave He–Ne laser operating at 633 nm was used as source of excitation. The open aperture Z-scan measurements indicated the sample displays reverse saturable absorption (RSA) process. The negative sign of the nonlinear refractive index n₂ was noted from the closed aperture Z-scan measurements indicates, the films exhibit self-defocusing property due to thermal nonlinearity. The third-order nonlinear optical susceptibility χ(3) varies from 8.17 × 10⁻⁵ esu to 1.39 × 10⁻³ esu with increase in electron beam irradiation. The present study reveals that the irradiation of electron beam leads to significant changes in the third-order optical nonlinearity. Al doped ZnO displays good optical power handling capability with optical clamping of about ∼5 mW. The irradiation study endorses that the Al doped ZnO under investigation is a promising candidate photonic device applications such as all-optical power limiting.     

Structural,optical and dielectric studies of novel non-linear Bisglycine Lithium Nitrate piezoelectric single crystal

The novel non-linear semiorganic Bisglycine Lithium Nitrate (BGLiN) single crystals were grown by slow evaporation technique. The structural analysis revealed that it belongs to non-centrosymmetric orthorhombic structure. The presence of various functional groups in the grown crystal was confirmed by FTIR and Raman analysis. Surface morphology of the grown crystal was studied by scanning electron microscopy. The optical studies show that crystal has good transmittance (more than 80%) in the entire visible region and a wide band gap (5.17 eV). The optical constants such as extinction coefficient (K), the reflectance (R) and refractive index (n) as a function of photon energy were calculated from the optical measurements. With the help of these optical constants the electric susceptibility (χ_c) and both the real (ε_r) and imaginary (ε_i) parts of the dielectric constants were also calculated which are required to develop optoelectronic devices. In photoluminescence studies, a broad emission band centered at 404 nm was found in addition to a small band at 352 nm. A broad transition (from 29 to 33 °C) was observed with low dielectric constant value. A high piezoelectric charge coefficient (d₃₃) of 14 pC/N was measured at room temperature which implies its usefulness for various sensor applications. The second harmonic generation efficiency of crystal was found to be 1.5 times to that of KDP. From thermo gravimetric analysis and differential thermal analysis, thermal stability and melting point (246 °C) were investigated. The dielectric behavior, optical characterization, piezoelectric behavior and the non-linear optical properties of the Bisglycine Lithium Nitrate single crystals were reported for the first time which established the usefulness of these crystals for various piezo- and opto-electronics applications.     

Effect of oxygen partial pressure on microstructural and optical properties of titanium oxide thin films prepared by pulsed laser deposition

Nanocrystalline titanium oxide (TiO₂) thin films were deposited on silicon (1 0 0) and quartz substrates at various oxygen partial pressures (1 × 10⁻⁵ to 3.5 × 10⁻¹ mbar) with a substrate temperature of 973 K by pulsed laser deposition. The microstructural and optical properties were characterized using Grazing incidence X-ray diffraction, atomic force microscopy, UV–visible spectroscopy and photoluminescence. The X-ray diffraction studies indicated the formation of mixed phases (anatase and rutile) at higher oxygen partial pressures (3.5 × 10⁻² to 3.5 × 10⁻¹ mbar) and strong rutile phase at lower oxygen partial pressures (1 × 10⁻⁵ to 3.5 × 10⁻³ mbar). The atomic force microscopy studies showed the dense and uniform distribution of nanocrystallites. The root mean square surface roughness of the films increased with increasing oxygen partial pressures. The UV–visible studies showed that the bandgap of the films increased from 3.20 eV to 3.60 eV with the increase of oxygen partial pressures. The refractive index was found to decrease from 2.73 to 2.06 (at 550 nm) as the oxygen partial pressure increased from 1.5 × 10⁻⁴ mbar to 3.5 × 10⁻¹ mbar. The photoluminescence peaks were fitted to Gaussian function and the bandgap was found to be in the range ∼3.28–3.40 eV for anatase and 2.98–3.13 eV for rutile phases with increasing oxygen partial pressure from 1 × 10⁻⁵ to 3.5 × 10⁻¹ mbar.     

Effect of tellurium addition on the optical and physical properties of germanium selenide glassy semiconductors

Thin films of the glasses Ge₁₀ Se_90−x Te_x (0 ≤ x ≥ 40) have been prepared by melt quenching technique; thin films were evaporated at a pressure of ≈10⁻⁴ Pa. The optical absorption behavior of these thin films was studied from the reflection and transmission spectrum in the spectral range 200-1200 nm. The optical constants i.e optical band gap (E_opt), absorption coefficient, refractive index (n) are calculated. The optical band gap has been estimated using Tauc extrapolation and found to decrease with Te content. The Dispersion of refractive index has been studied in terms of Wemple - Di Domenico model. The value of static refraction index has been found to increase with Te content. The distribution of the possible chemical bonds has been calculated. The obtained results were correlated with the character of the chemical bond for the prepared compositions through a study of parameters such as average heat of atomization (Hs), the cohesive energies of the bonds (CE), The mean bond energy <E> and average coordination number (m).     

Growth and nonlinear optical properties of Zn-doped LiB3O5 crystals

Zn-doped LiB₃O₅ (LBO) single crystals with high quality were successfully grown from the Li₂O–MoO₃–ZnF₂ ternary system by the top-seeded solution growth method. The suitable region for LBO crystal growth was investigated by growth experiments, as well as viscosity and volatility measurements, which confirmed that the optimal molar ratio of Li₂O:MoO₃:ZnF₂ was 1:1.5:0.2. The second-harmonic generation efficiency of Zn-doped LBO crystal increased by 16% compared with that of the LBO crystals grown from the MoO₃ flux. The optical homogeneity was at 10⁻⁶ cm⁻¹. Optical absorption at the critical wavelengths of 1064 nm was measured to be 15 and 18 ppm cm⁻¹, respectively.     

Synthesis,growth, and two-photon absorption induced optical limiting action of cytosinium benzoate single crystal

Two-photon absorption induced optical limiting action was demonstrated in cytosinium benzoate (CB) under nanosecond laser (532 nm, 9 ns, and 10 Hz) excitation. Intensity dependent open aperture Z-scan experiment exposed the presence of reverse saturable absorption ascribed due to sequential two-photon absorption. Initially CB single crystals were grown at room temperature by slow evaporation solution technique. Single crystal XRD shows that CB belongs to monoclinic crystal system with P2₁/c space group. Fourier Transform Infrared spectrum was recorded to identify the presence of functional groups. Thermal studies shows that the crystal is stable upto 168 °C. Vickers microhardness studies confirm that the grown crystal was belongs to soft material category. Etching study shows linear rectangular etch patterns (5 s) and well defined stacking planes (10 s) for water etchant. Optical studies demonstrate that CB crystal possess lower cut-off (287 nm) and moderate linear transmittance in visible region. The optical energy band gap of CB crystal was estimated from photoluminescence studies as 3.1 eV. CB with higher two-photon absorption coefficient (1.26?×?10^–10 m/W) and lower onset limiting threshold (1.92?×?10¹² W/m²) can be a potential candidate for developing laser safety devices under nanosecond green laser excitation regime.

     

Bulk crystal growth,spectral, optical,thermal, electrical and third-order NLO properties of benzylidene malononitrile derivative single crystal: a promising material for nonlinear optical device applications

Bulk organic intramolecular charge transfer nonlinear optical single crystal of 2-(2,4-dimethoxybenzylidene) malononitrile (DMM) with the sizes of 24?×?18?×?13 mm³ have been successfully grown by slow evaporation solution growth technique at 35 °C using acetone as the solvent. The lattice parameters of the grown DMM crystal was evaluated by single crystal X-ray diffraction analysis. The optical transmittance (T) data was taken from the well-polished crystal of DMM, and cut-off wavelength (λ?=?483 nm) was identified by UV–Vis spectral studies. Thermal stability and melting point (145.78 °C) were studied with TGA–DSC analysis. The low value of the dielectric constant (ε_r) of DMM suggests that the crystal can be used in the microelectronics industry. The laser-induced damage threshold experiment shows that the grown DMM bulk crystal possess an excellent resistance to laser radiation with a high threshold up to 1.75 GW/cm², much larger than those of several known organic and inorganic NLO materials. The DMM crystal exhibits positive optical non-linearity and reverse saturation absorption. It also exhibited a nonlinear refractive index (n₂) in the order of 10^?11 m²/W, a nonlinear absorption coefficient (β) in the order of 10^?5 m/W, third order non-linear susceptibility (χ⁽³⁾) in the order of 10^?5 esu and a second-order molecular hyperpolarizability (γ) in the order of 10^?33 esu. All the above results indicate that DMM has a potential application as a useful NLO candidate.     

Synthesis,crystal growth,structural, spectral,thermal, mechanical,linear and nonlinear optical studies of organic single crystal 4-Iodo 4-nitrostilbene (IONS): A potential NLO material

An organic nonlinear optical material 4-Iodo 4-nitrostilbene (IONS) has been synthesized and good optical quality single crystal was grown from ethyl methyl ketone solvent by the solution growth technique. Single and powder X-ray diffraction analyses reveals that the grown crystal belongs to monoclinic crystal system with noncentrosymmetric space group ‘P2₁’ and it has good crystalline nature. Functional groups and molecular structure of the title compound were confirmed by FTIR and ¹H NMR respectively. The UV–Vis–NIR absorption study reveals no absorption in the visible region and the cut-off wavelength was found to be at 412.84 nm, TG/DTA, mass spectral analysis, photoluminescence and microhardness studies have been carried out for the grown crystals and results are discussed in detail. The second harmonic efficiency of the IONS was determined by Kurtz–Perry powder technique which reveals that the IONS crystal (3.1 V) has greater efficiency i.e., 143 times to that of KDP (21.7 mV).     

Structural,optical, thermal,photoconductivity, laser damage threshold and fluorescence analysis of an organic material: β-P-amino benzoic acid single crystal

β-P-amino benzoic acid, an organic single crystal was grown by slow evaporation technique. Single crystal X-ray diffraction studies show that the grown crystal has β-polymorph of P-amino benzoic acid [β-PABA] form and the lattice parameters are a = 6.30 Å, b = 8.61 Å, c = 12.43 Å α = γ = 90° and β = 100.20°. FTIR analysis confirms that bands at 1588 cm⁻¹, 1415 cm⁻¹ are assigned to ring skeletal vibrations of title compound. The molecular structure of the grown crystal has been identified by Nuclear Magnetic Resonance spectral study. The optical absorbance spectrum from 200 to 1100 nm shows that there is an edge absorbance in UV region. Optical band gap of the crystal has been assessed from the absorbance spectrum. The thermal properties of crystals were evaluated from TG-DTA analysis, it exhibits that there is no weight loss up to 187 °C. Laser damage threshold indicates that the grown crystal has no surface damage up to 35 mJ. Photoconductivity and fluorescence spectral experiments are also carried out and the results are discussed.     

Growth, thermal and spectroscopic characteristics of LiNd(WO4)2 crystal

Crystal growth, thermal and optical characteristics of LiNd(WO₄)₂ crystal have been investigated. The LiNd(WO₄)₂ crystal up to Ø15 × 32 mm³ has been grown by Czochralski technique. The hardness is about 5.0 Mohs’ scale. The specific heat at 50 °C is 0.42 J g⁻¹ K⁻¹. The thermal expansion coefficient for c- and a- axes is 1.107 × 10⁻⁵ and 2.104 × 10⁻⁵ K⁻¹, respectively. The absorption and fluorescence spectra and the fluorescence decay curve of LiNd(WO₄)₂ crystal were measured at room temperature. Some spectroscopic parameters such as the intensity parameters, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and emission cross sections were estimated.     

Effect of temperature on structural, optical and photoluminescence properties of antimony (Sb) doped polycrystalline CuInS2 thin films prepared by spray pyrolysis

Copper indium disulphide (CuInS₂) is an absorber material for solar cell and photovoltaic applications. By suitably doping CuInS₂ thin films with dopants such as Zn, Cd, Na, Bi, Sn, N, P and As its structural, optical, photoluminescence properties and electrical conductivities could be controlled and modified. In this work, Sb (0.01 mole (M)) doped CuInS₂ thin films are grown in the temperature range 300-400 °C on heated glass substrates. It is observed that the film growth temperature, the ion ratio (Cu/In = 1.25) and Sb-doping affects the structural, optical and photoluminescence properties of sprayed CuInS₂ films.The XRD patterns confirm that the Sb-doping suppresses the growth of CuInS₂ polycrystalline thin films along (1 1 2) preferred plane and in other characteristic planes. The EDAX results confirm the presence of Cu, In, S and Sb. About 60% of light transmission occurs in the wavelength range 350-1100 nm. The absorption coefficient (α) is found to be in the order of 10⁵ cm⁻¹. The band gap energy increases as the temperature increases from 300-400 °C (1.35-1.40 eV). SEM photographs depict that large sized crystals of Sb-doped CuInS₂ (1 μm) are formed on the surface of the films. Well defined sharp blue and green band emissions are exhibited by Sb-doped CuInS₂ thin films. Defects-related photoluminescence emissions are discussed. These Sb-doped CuInS₂ thin films are prepared by the cost effective method of spray pyrolysis from the aqueous solutions of CuCl₂, InCl₃, SC(NH₂)₂ and SbCl₃ on heated glass substrates.     

Studies on optical and mechanical properties of new organic NLO crystal: Guanidinium 4-aminobenzoate (GuAB)

Organic nonlinear optical crystal of guanidinium 4-aminobenzoate (GuAB) has been successfully grown by slow evaporation solution growth technique. The grown crystal is up to the dimension of 36 × 8 × 6 mm³. The crystal is characterized by single crystal XRD for obtaining unit cell parameters. Optical properties of the grown crystal have been studied by means of UV–Vis–NIR transmission and absorption spectra in the range of 200 to 1000 nm. The refractive index and band gap energy of the GuAB crystal are obtained as 1.68 and 3.73 eV respectively. Mechanical hardness has been carried out on the grown crystal.     

Optical and thermal properties of crystalline Tb: KLu(WO4)2

A single crystal of Tb: KLu(WO₄)₂ with dimensions of 40 mm × 40 mm × 18 mm has been grown by the top-seeded solution growth (TSSG) method. The color of the crystal is brown. Absorption and fluorescence spectra were measured at room temperature. The measured specific heat is a little lower than that of Yb: KLW (0.365 J/g K) at 90 °C. The measured mean linear coefficients of thermal expansion are α_a = 17.1643 × 10^− 6 K^− 1_, α_a^⁎ = 14.0896 × 10^− 6 K^− 1, α_b = 8.7938 × 10^− 6 K^− 1, α_c = 23.1745 × 10^− 6 K^− 1, α_c^⁎ = 20.2866 × 10^− 6 K^− 1. The results indicate that the crystal has a large anisotropy. The refractive index was measured.     

Optical and dielectric properties of nitrophenolate based nonlinear optical crystal

A semi-organic nonlinear optical (NLO) material, lithium-p-nitrophenolate trihydrate (LPNP) was synthesized. Single crystals of dimensions 20 × 7 × 3 mm³ were harvested following the solvent evaporation technique. The functional groups present in the compound were identified from FT-IR and FT-Raman spectral analyses, and its molecular structure was confirmed. Identification of the compound was accomplished by X-ray diffraction technique (powder and single crystal XRD). The unit-cell dimensions and the morphology of the grown crystals were identified from single crystal XRD measurements. The thermal transport properties, thermal effusivity (e), thermal diffusivity (α), thermal conductivity (k) and heat capacity (C _p) were measured by the photopyroelectric technique at room temperature. Dielectric constant and dielectric loss were also measured as a function of frequency between 42 Hz and 5 MHz, and temperature between 32 and 100 °C. From optical transmittance measurements, the direct optical band gap of the LPNP crystal was estimated to be 2.47 eV. Laser damage threshold is 60.91 GW cm⁻². Powder second harmonic generation (SHG) measurement was carried out using a modified Kurtz–Perry technique. Third order nonlinear response was studied using Z-scan technique with a He–Ne laser (632.8 nm, 35 mW). The magnitude and the sign of the nonlinear absorption and nonlinear refraction are derived from a transmittance curve. The NLO parameters Intensity dependent refractive index n ₂, nonlinear absorption coefficient β and third order susceptibility χ⁽³⁾ were estimated.     

Influence of ultraviolet irradiation on the optical properties of amorphous Sb10Se90 thin films

Amorphous Sb₁₀Se₉₀ thin films were prepared by thermal evaporation of the bulk glass. The changes in the optical properties (transmittance, optical gap, absorption coefficient, refractive index and extinction coefficient) have been measured in the wavelength range 500-900 nm of virgin and ultraviolet (UV) illuminated films. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It is found that the optical energy gap decreases (photo-darkening) and the refractive index increases with the increase of UV exposure time. The dispersion of the refractive index (n) has been discussed in terms of Wemple-Didomenico single oscillator model. The oscillator energy E₀ and the dispersion energy E_d have been determined and discussed in terms of UV exposure time. The photo-darkening was discussed in terms of some of the current literature models.     

Composition dependence of structural and optical properties of Ba(Zrx,Ti1-x)O3 thin films grown on MgO substrates by pulsed laser deposition

Ba(Zr_x,Ti_1-x)O₃ (BZT) films with Zr concentration ranging from 0 to 40% were grown on MgO single crystal substrates by pulsed laser deposition, and their optical properties in the visible range were systematically characterized. A linear increase in the out-of-plane lattice constant of BZT unit cell with increasing Zr content was detected by X-ray diffraction. The surface morphology was observed by atomic force microscopy and the grain size was shown to increase with Zr concentration. Prism coupling and UV-visible transmission spectroscopy techniques were used to analyze the optical properties of the films. Refractive index between 2.15 and 2.3 was observed at 633 and 1547 nm respectively, which decreased with rising Zr content. The BZT films also possessed large optical band gap energy up to 3.92 eV, which increased with rising Zr content. Quadratic electro-optic effect was observed with electro-optic coefficients between 0.11 and 0.81 × 10^− 18 m²/V², which decreased with Zr concentration. Optical loss was estimated from scattering and absorption, and the absorption coefficient dropped with increasing Zr content at near band gap. The obtained results provide information for the design of BZT thin film-based optical devices.     

Growth and characterization of l-phenylalanine nitric acid, a new organic nonlinear optical material

A new organic nonlinear optical material L-phenylalanine nitric acid [2C₉H₁₁NO₂.H⁺. NO₃⁻] (LPN), was synthesized in mixed solvent of deionised water and methanol and single crystals of LPN was grown by slow evaporation method. Transparent crystals upto 2.9 × 0.3 × 0.05 cm³ were obtained. The grown crystals have been subjected to powder X-ray diffraction studies to identify the crystalline nature. Single crystal X-ray diffractometer was utilized to measure unit cell parameters and to confirm the crystal structure. The modes of vibration of different molecular groups present in LPN were identified by FTIR spectral analysis. Transmission spectra reveals that the crystal has low UV cutoff of 295 nm and has a good transmittance in the entire visible region enabling its use in optical applications. Thermal properties of the crystals have been investigated using thermogravimetric (TG) and differential thermal analyses (DTA), which indicate that the material does not decompose before melting. The existence of second harmonic generation signals was observed using Nd:YAG laser with fundamental wavelength of 1064 nm.     

Raman study of surface optical phonons in hydrothermally obtained ZnO(Mn) nanoparticles

Nanocrystalline samples of ZnO(Mn) were synthesized by hydrothermal method. The morphology of the samples was studied by HRTEM and SEM. X-ray diffraction was used to determine composition of the samples (ZnO and ZnMn₂O₄) and the mean crystalline size (from 16 to 99 nm). In this paper we report the experimental spectra of Raman scattering (from 100 to 1600 cm⁻¹) with surface optical phonons (SOP) in range of 497–538 cm⁻¹ as well as formation of new phases MnO, Mn₃O₄ and ZnMnO₃. The phonon of registered phase's exhibit effects connected to phase concentration, while the SOP phonon mode exhibit significant confinement effect.