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1.
Polycrystalline β ‐GaSe thin films were obtained by the thermal evaporation of GaSe crystals onto glass substrates kept at 300 °C under a pressure of 10–5 Torr. The transmittance and reflectance of these films was measured in the incident photon energy range of 1.1–3.70 eV. The absorption coefficient spectral analysis in the sharp absorption region revealed a direct allowed transitions band gap of 1.83 eV. The data analysis allowed the identification of the dispersive optical parameters by calculating the refractive index in the wavelength region of 620–1100 nm. In addition, the photocurrent of the samples was studied as function of incident illumination‐intensity and temperature. The photocurrent is found to exhibit sublinear and supralinear character above and below 270 K, respectively. The temperature dependent photocurrent data analysis allowed the calculation of photocurrent activation energies as 603, 119 and 45 meV being dominant in the temperature regions of 250–300 K, 180–240 K and 80‐160 K, respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
H. Karaaa M. Parlak O. Karabulut U. Serincan R. Turan B. G. Ak&#x;nolu 《Crystal Research and Technology》2006,41(12):1159-1166
Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X‐Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 × 109 to 6.5 × 105 Ω‐cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as‐grown, 36 and 472 meV for as‐implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500°C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (IPC) and illumination intensity (Φ) was studied and it was observed that the relation obeys the power law, IPC αΦn with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as‐grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge‐implanted sample was observed with increasing annealing temperatures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
Polycrystalline cadmium doped gallium selenide thin films were obtained by the thermal co‐evaporation of GaSe crystals and Cd grains onto glass substrates. The structural, compositional and optical properties of these films have been investigated by means of X‐ray diffraction, energy dispersive X‐ray analysis and UV‐visible spectroscopy techniques, respectively. Particularly, the elemental analysis, the crystalline nature, the energy band gap, the refractive index, the dispersion energy and static dielectric constant have been identified. The absorption coefficient spectral analysis in the sharp absorption region revealed a direct forbidden energy band gap of 1.22 eV. The cadmium doping has caused a significant decrease in the values of the energy band gap and in all the dispersive optical parameters, as well. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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5.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,626(1):108-114
The binary mixture of two compounds, viz., Cholesteryl laurate (CL) and diethyl 4, 4′-azoxy benzoate shows the cholesteric and smectic phases sequentially when the specimen is cooled from its isotropic phase. Refractive indices, birefringence, and optical transmittance have been measured by the optical technique. With the help of measured data, the macroscopic ordered parameter has been discussed. The temperature dependence of these parameters has also been discussed. 相似文献
6.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,626(1):141-150
The multicomponent system of cholesteryl linolenate (CL), sodium oleate (Naol), and orthophosphoric acid (H3PO4) exhibits liquid crystalline mesophases, like cholesteric and smectic phases, such as SmA, SmC, SmB, and SmG sequentially when the specimen is cooled from its isotropic phase. These phases have been observed by using microscopic technique. Helfrich potential and elastic moduli have also been estimated in the smectic phase using Helfrich model. Optical transmittance and electrical conductivity have also been discussed. 相似文献
7.
Photoluminescence (PL) spectra of Tl4Ga3InSe8 layered crystals grown by Bridgman method have been studied in the wavelength region of 600‐750 nm and in the temperature range of 17‐68 K. A broad PL band centered at 652 nm (1.90 eV) was observed at T = 17 K. Variations of emission band has been studied as a function of excitation laser intensity in the 0.13 to 55.73 mW cm‐2 range. Radiative transitions from donor level located at 0.19 eV below the bottom of conduction band to shallow acceptor level located at 0.03 eV above the top of the valence band were suggested to be responsible for the observed PL band. From X‐ray powder diffraction and optical absorption study, the parameters of monoclinic unit cell and the energy of indirect band gap were determined, respectively. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,626(1):151-159
In the present work, our investigation is to study the optical anisotropic properties of the binary mixture of cyano-benzilidene-p-n-octyl-oxy-aniline (CBOOA), cholesteryl nonanoate (CN), which exhibits a very interesting liquid crystalline Cho-TGB-SmC-SmA-SmB phases sequentially when the specimen cooled from its isotropic phase. These phases have been characterized by using microscopic and optical anisotropic technique. The temperature variations of optical anisotropy and electrical conductivity have been discussed. X-ray studies are supported to calculate the nano-aggregated grain size of the molecules. 相似文献
9.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,624(1):20-27
We report the results of our studies on optical and thermal properties of ternary mixture of three compounds viz., 4′-n-octyl-4-cyanobiphenyl (8CB), didodecyl dimethyl ammonium bromide, and glacial acetic acid. Higher concentrations of the given mixture show a very interesting reentrant nematic phase, sequentially when the specimen is cooled from its isotropic melt at different temperatures. The temperature variations of optical anisotropy, optical textures, and electrical conductivity have also been discussed. Nanoaggregated size of the molecules has been confirmed by X-ray studies. 相似文献
10.
Synthesis of linked ZnO micro rods by microwave radiation and its characterization is presented in this report. In this simple microwave assisted solution phase route zinc nitrate and hexamethylenetetramine has been used as the starting materials for the synthesis of linked ZnO rods. Linked ZnO rods with various morphologies such as bipods, tripods, tetrapods and etc have been prepared. The influence of irradiation time of microwave on the formation of linked ZnO rods was investigated. X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive spectroscopy (EDS) were used for the characterization of the product. The FESEM images showed ZnO rods of diameter in the range of 100‐200 nm and length around 5000 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
O. Karabulut M. Parlak R. Turan U. Serincan B. G. Ak&#x;nolu 《Crystal Research and Technology》2006,41(3):243-249
The structure and temperature dependent spectral photoconductivity of as‐grown and N‐and Si‐implanted GaSe single crystals have been studied. It was observed that post‐annealing results in a complete recovery of the crystalline nature that was moderately reduced upon implantation. The band edge is shifted in the implanted sample which is attributed to the structural modifications and continuous shallow levels introduced upon implantation and annealing. Our calculations showed that the trap density is increased upon implantation and annealing which confirms a possibility of explanation the phenomenon within a framework of continuous trap levels. Photocurrent measurements as a function of photo‐excitation intensity also support continuous distribution of localized states in the band gap. © 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim 相似文献
12.
We report first to date ‘green’ metalorganic‐free synthesis of colloidal GaSe nanocrystals. Structure and optical properties of gallium selenide nanocrystals dispersed in oleylamine are discusses in respect to that conventionally prepared in alkylphosphonic solutions. We explore the organization of the particles into nanowires and propose appropriate growth mechanism. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
Raman spectra of GaSe layered crystal have been measured using a He‐Ne laser and temperature tuning the free‐ to‐bound gap in the range 10‐290 K. Resonance enhancement of E″(2) mode has been observed for both incident and scattered photon energies equal to the free‐to‐bound transition energy. 相似文献
14.
T. N. Govindaiah H. R. Sreepad Nagappa J. Mahdeva 《Molecular Crystals and Liquid Crystals》2014,593(1):43-50
We report the results of our studies on the optical and thermal properties of binary mixture of compounds, viz., Berberine (BBE) and Poly-ethylene glycol (PEG). The mixture shows very interesting coexistent biphasic regions N + I and N + C phases respectively at different concentrations of BBE sequentially when the specimen is cooled from its isotropic liquid phase. The temperature variations of optical anisotropy and optical textures have also been discussed. Formation of above molecular orientations has been confirmed by X-ray studies. 相似文献
15.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,626(1):100-107
The multi-component system of cholesteryl chloride (ChCl), dodecyl trimethylammonium chloride (DTAC), and ethylene glycol (EG) exhibits very interesting liquid crystalline mesophases like cholesteric and SmA, SmC, and SmB phases sequentially when the specimen is cooled from its isotropic phase. These phases have been characterized by employing optical and X-ray studies. Pitch of the cholesteric phase has been calculated and discussed. Variation of pitch from the cholesteric phase to smectic phase is smooth and continuous. The temperature variation of optical anisotropy and electrical-conductivity has also been discussed. It has been found that wherever there is a phase transition, the value of electrical susceptibility changes appreciably. 相似文献
16.
We report the results of our studies on the optical and thermal properties of two nonmesogenic compounds, namely, Cetyl-dimethyl-ethylammonium bromide (CDEAB) and Glacial acetic acid. The mixture exhibits very interesting schilieren texture of micellar nematic phase, SmA, SmC*, and SmE phases, respectively, at different concentrations of CDEAB sequentially when the specimen is cooled from its isotropic phase. The order parameter (S) of the micellar nematic phase is estimated with the help of temperature dependence of optical anisotropy from the measured values refractive index and density data. The temperature variation of order parameter of the experimental curve is very well fitted with the Mayer–Saupe theoretical curve. X-ray studies have been discussed. The formation of above phases has been confirmed by optical and DSC studies. 相似文献
17.
T. N. Govindaiah 《Molecular Crystals and Liquid Crystals》2016,626(1):124-129
We report the results of our studies on the optical and thermal properties of binary mixture of two compounds viz., abietic acid and alizarin dye. The mixture shows a very interesting co-existent biphasic regions of nematic (N + I) and columnar smectic (C + I) phases, sequentially when the specimen is cooled from its isotropic phase respectively at different concentrations of given molecule. The temperature variations of optical anisotropy, optical textures and electrical conductivity have also been discussed. Aggregated molecular size has been confirmed by X-ray studies. 相似文献
18.
O. Karabulut M. Parlak K. Yilmaz R. Turan B. G. Akinoglu 《Crystal Research and Technology》2003,38(12):1071-1076
GaSe single crystals grown by Bridgman method have been doped by ion implantation technique. The samples were bombarded in the direction parallel to c‐axis by Si ion beam of about 100 keV to doses of 1 × 1016 ions/cm2 at room temperature. The effects of Si implantation with annealing at 500 and 600 °C on the electrical properties have been studied by measuring the temperature dependent conductivity and photoconductivity under different illumination intensities in the temperature range of 100–320 K. It is observed that Si implantation increases the room temperature conductivity 10−7 to 10−3 (Ω‐cm)−1 depending on the post annealing temperature. The analysis of temperature dependent conductivity shows that at high temperature region above 200 K, the transport mechanism is dominated by thermal excitation in the doped and undoped GaSe samples. At lower temperatures, the conduction of carriers is dominated by variable range hopping mechanism in the implanted samples. Annealing of the samples at and above 600 °C weakens the temperature dependence of the conductivity and photoconductivity. This indicates that annealing of the implanted samples activates Si‐atoms and increases structural deformations and stacking faults. The same behavior was observed from photoconductivity measurements. Hence, photocurrent‐illumination intensity dependence in the implanted samples obeys the power low Ipc ∝ Φn with n between 1 and 2 which is an indication of continuous distribution of localized states in the band gap. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
本文利用低温光致发光谱(PL)研究了Fe掺杂GaN晶体非极性a面{1120}、m面{1100} 的带边峰和Fe3+相关峰(4T1(G)- 6A1(S))的偏振发光特性。结果表明:a面与m面光学各向异性差别较小,线偏振光的电矢量E平行于c轴[0001]时(E∥c),GaN带边峰强度最小,而Fe3+零声子峰(1.299 eV)强度最强。带边峰线偏振度小,而Fe3+零声子峰线偏振度大,a面带边峰的线偏振度为26％,Fe3+零声子峰的偏振度在a面和m面分别达到55%和58%。在5 K低温下,进一步测量了Fe3+精细峰和声子伴线的偏振特性,结果表明,除了一个微弱的峰外,其他精细峰和声子伴线与Fe3+零声子峰偏振特性一致。本研究有助于拓展Fe掺杂GaN晶体材料在新型偏振光电器件领域的应用。 相似文献
20.
本文采用普适的固相法合成一种新型硅酸盐K3(Y0.88Yb0.10Ho0.02)Si2O7荧光粉,并系统研究样品的上转换光致发光和光学测温性能。研究表明,在980 nm激发下,K3(Y0.88Yb0.10Ho0.02)Si2O7荧光粉表现出红光发射,主发射峰位于665 nm,归属于Ho3+的5F5→5I8跃迁。通过对发光强度和激发功率的对数变换,研究荧光粉的上转换机制和可能导致的上转换的光子反应,证明(5S4,5F2)→5I8跃迁上转换发光机制为三光子机制,5F5→5I8跃迁则为双光子机制。K3(Y0.88Yb0.10Ho0.02)Si2O7荧光粉的5F5/(5F4,5S2)的非热耦合能级的荧光强度比结果表现出其良好的光学测温潜力,经计算其最大灵敏度约为0.17 K-1 (423 K)。 相似文献