共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Abu El-Fadl 《Crystal Research and Technology》1999,34(8):1047-1054
The effect of temperature on the optical absorption spectra and optical parameters is investigated for pure TGS and TGS doped with Cu2+ ions. Absorption measurements cover the range from room temperature to about 355 K in the energy range 3-5.5 eV. The temperature dependence of the band gap Eg(T) reveals an anomaly at the phase transition temperature for both pure and Cu2+-doped TGS crystals. In the region of the absorption edge the absorption coefficient is found to display Urbach-rule behaviour. The characteristic Urbach parameters are determined and their temperature dependence is investigated. 相似文献
2.
A study of the optical properties of pure‐and some metal ions doped ammonium sulfate crystals (AS) were made. Optical constants of AS crystals were calculated at room temperature. The optical absorption coefficient (α ) was analyzed and interpreted to be in the allowed direct transition. The introduction of Rb+ or Cs+ ions gives rise to an intense charge transfer band with a maximum at λ= 310 nm in the optical spectrum. In case of Cr3+ ‐doping, the absorption shows a shoulder just before the onset band to band transition. The values of the allowed direct energy gap Eg for undoped and doped crystals were calculated. It was found that Eg values were decreased with metal ions doping. The refractive index, the extinction coefficient and both the real and imaginary parts of the dielectric permittivity were calculated as a function of photon energy. The validity of Cauchy‐Sellimeier equation was checked in the wavelength range 4.9 ‐ 5.6 eV and its parameters were calculated. Applying the Single‐Effective‐Oscillator model, the moments of ε (E ) could be estimated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
Xiaolong Yang Guanfeng Xu Heping Li Jianguo Zhu Xiu Wang 《Crystal Research and Technology》1996,31(4):521-527
The optical transmittance of LiNbO3 single crystal double doped with MgO and ZnO was measured from the ultraviolet to the visible range. The wavelength dependence of the absorption coefficient α and its root α1/2 (α versus hv and α1/2 versus hv, respectively) were calculated and the characteristics of the absorption edge were discussed. The energy gaps Eg and Eg of the crystals which correspond to the direct transition and the indirect transition, respectively, and the energy of phonons taking part in the indirect transition were calculated. The effects of dopants Mg and Zn on the optical absorption properties are discussed. It was found that the energy Eg of our sample which was double doped with MgO and ZnO was smaller than that of congruent LN, causing the indirect transition absorption edge to move towards the infrared. 相似文献
4.
V. I. Stadnik 《Crystallography Reports》2005,50(4):654-660
The effect of uniaxial mechanical pressure along the main crystallophysical axes on the principal values of birefringence Δn i in TGS crystals doped with 5% D-serine is investigated. It is ascertained that the values of Δn i are rather sensitive to the action of uniaxial stresses. The temperature shift coefficients ?T c /?σm are determined for the phase-transition points. The temperature and spectral dependences of the combined piezo-optic constants π im 0 are calculated. The contribution of the secondary electro-optic effect to the changes in the birefringence and the piezo-optic constants of doped crystals is determined. It is found that the piezooptic constants π 23 0 and π 12 0 have the same values, which indicates a decrease in the anisotropy of the optical indicatrix of doped crystals under the action of uniaxial stress. The optical and deformation contributions to the relaxation effect of piezo-optical birefringence in doped TGS crystals are found. 相似文献
5.
The effect of electron‐beam irradiation with different doses on optical constants of (NH4)2ZnCl4: x Sr2+ crystals with x=0.000, 0.020, 0.039, 0.087 or 0.144 wt% has been studied. The optical transmission in the energy range 3.4‐6.4 eV was measured hence the absorption coefficient was computed as a frequency function. The absorption coefficient was also calculated as a function of electron‐beam dose. Irradiation with e‐beam did not affect the allowed indirect type of transition responsible for interband transitions of (NH4)2ZnCl4: x Sr2+ crystals. Values of the optical energy gap Eg and optical moment Ep for electronic interband transition of unexposed and (NH4)2ZnCl4: x Sr2+ crystals after e‐beam exposure were deduced. The area under the absorption band at 5.30 eV was used to evaluate the effect of e‐irradiation on optical parameters of samples with x=0.00, 0.020 or 0.039. A shift in the position and a nonmonotonic change in the intensity of this band with increasing e‐beam dose was observed. Changes in the Eg value were used to evaluate the effect of e‐beam exposure dose on (NH4)2ZnCl4: x Sr2+ samples with x=0.087 or 0.144. The obtained results were compared with those obtained for the same crystals after irradiation with different γ‐doses. 相似文献
6.
K. Velavan R. V. S. S. N. Ravikumar R. Venkatesan P. Sambasiva Rao 《Crystal Research and Technology》2004,39(5):448-453
The optical absorption spectra of Ni(II) doped hexaimidazole zinc(II) dichloride tetrahydrate (HZDT) and Cu(II) doped magnesium potassium phosphate hexahydrate (MPPH) have been studied at room temperature. Ni(II)/HZDT spectrum consists of three strong and one weak band. The calculated value of Dq is 1051 cm‐1 and the interelectron repulsion parameters B and C are 854 and 3626 cm‐1 respectively. The correlation of optical work with EPR has yielded the spin‐orbit interaction parameters λ and ξ as –225 and –450 cm‐1 respectively. The symmetry around the Ni(II) ion is distorted octahedral, as suggested by EPR results. The estimated percentage covalency of the nickel‐nitrogen bond is around 30%. The optical absorption studies of Cu(II)/MPPH show three bands, which are identified as 2B1g → 2A1g, 2B1g → 2B2g and 2B1g → 2Eg transitions. The octahedral field parameter Dq and the tetragonal field parameters have been evaluated from the observed adsorption bands. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
7.
N. Tigau 《Crystal Research and Technology》2007,42(3):281-285
Sb2S3 thin films are obtained by evaporating of Sb2S3 powder onto glass substrates maintained at room temperature under pressure of 2×10‐5 torr. The composition of the thin films was determined by energy dispersive analysis of X‐ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X‐ray diffraction (XRD) technique and scanning electron microscopy (SEM). The as‐deposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as‐deposited and annealed Sb2S3 thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400‐1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E0, dispersion energy, Ed) were determined. The static refractive index n(0), static dielectric constant, ε∞, and optical band gap energy, Eg, were also calculated using the values of dispersion parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
Single crystals of CdAl2S4 and CdAl2Se4 showing high transparency were grown by the chemical vapour transport method. Their composition was proven by microprobe analysis. Structural investigations were done by Rietveld refinements and are in good agreement with known structure data. From transmittance and reflectance measurements the energy of the band gap WBS estimated. Assuming a direct nature of the corresponding optical transition the following values were obtained: Eg = 3.82 eV (RT), Eg = 3.94 eV (85 K) for CdAl2S4 and Eg = 2.95 eV (RT), Eg = 3.07 eV (85 K) for CdAl2Se4 respectively. 相似文献
9.
K. Santhosh Kumar C. Manoharan L. Amalraj S. Dhanapandian G. Kiruthigaa K. Vijayakumar 《Crystal Research and Technology》2012,47(7):771-779
Undoped and Indium doped tin disulphide (SnS2) thin films had been deposited onto glass substrates at Ts = 300 °C using spray pyrolysis technique under atmospheric pressure with stannous chloride, indium chloride and thiourea as precursors. The structural, optical and electrical properties of the deposited films were characterized. The XRD pattern revealed that the undoped and doped films had preferred orientation along (002) plane with hexagonal structure. FESEM micrographs had shown that morphologies of the films changed with indium doping. Optical constant such as refractive index (n), extinction coefficient (k), real and imaginary parts of dielectric constants were evaluated from transmittance and reflectance spectra in UV‐Visible spectroscopy. The optical absorption data were used to determine the band gap energy and it was found to be 2.75 eV for undoped and 2.50 eV for indium doped films respectively. The room temperature dark resistivity was found to be 4.545 × 103 Ω‐cm and 5.406 × 103 Ω‐cm for undoped and In‐doped films respectively. 相似文献
10.
C. Viswanathan V. Senthilkumar R. Sriranjini D. Mangalaraj Sa. K. Narayandass Junsin Yi 《Crystal Research and Technology》2005,40(7):658-664
Thin films of InSe were obtained by thermal evaporation techniques on glass substrates maintained at various temperatures (Tsb = 30°, 400°C). X‐ray diffraction analysis showed the occurrence of amorphous to polycrystalline transformation in the films deposited at higher substrate temperature (400°C). The polycrystalline films were found to have a hexagonal lattice. Compositions of these films have been characterized by EDAX and the surface analysis by scanning electron microscopy. Optical properties of the films, investigated by using spectrophotometer transmittance spectra in the wavelength range (300 – 1100 nm), were explained in terms of substrate temperatures. Films formed at room temperature showed an optical band gap (Egopt) 1.56 eV; where as the films formed at 400°C were found to have a Egopt of 1.92 eV. The increase in the value of Egopt with Tsb treatment is interpreted in terms of the density of states model as proposed by Mott and Davis. The analysis of current ‐Voltage characteristics, based on space charge limited currents (SCLC) measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
Single crystals of the HgGaInS4 layered compound were grown by the iodine transport technique. Results of their optical, photoelectric, and radiative properties' study are presented. The band gap and the binding energy of holes on the sensitizing centres were determined to be Eg = 2.41 eV and Ea = 0.2 eV, respectively. A presence of quasi-continuously distributed states was stated which are responsible for the exponential segment of the absorption edge and which take part in the radiative recombination. 相似文献
12.
W. Hrig G. Kühn W. Mller A. Müler H. Neumann E. Reccius 《Crystal Research and Technology》1979,14(2):229-242
The electrical and optical properties of CuGaTe2 single crystals were investigated by resistivity and Hall effect measurements in the temperatur range T = 77… 300 K and optical transmission measurements in the temperature range T = 20… 300 K at photon energies hν = 1.15…1.50 eV. All samples were p-type conducting due to shallow acceptors with ionization energies EA1 ≈︁ 10−3 eV and concentrations NA1 ≈︁ p = (2…4). 1018 cm−3. The absorption spectra could be described by simultaneous consideration of acceptor - to - conduction band transitions with EA2 = 360 meV and NA2 ≈︁ 1022 cm−3 and valence band - to - conduction band transitions with EG = 1.24 eV at room temperaure. The temperature coefficient of the fundamental edge is dEG/dT = −4.0. 10−4 eV/K. The results are discussed with regard to some general trends found in the Cu-III–VI2 compounds. 相似文献
13.
A. V. Shil’nikov V. A. Fedorikhin B. A. Strukov N. V. Ratina 《Crystallography Reports》2004,49(3):443-449
Dielectric responses of several crystals in ultraweak measuring fields at low and infralow frequencies are compared, namely, of nominally pure, Cr-and Lα-alanine-doped triglycine sulfate (TGS) crystals and TGS + Cr3+ crystals irradiated with X-rays. It is shown that dopant-induced bias fields give rise to crystal unipolarity, suppress the domain contribution to their dielectric response, and diffuse the phase transition. It is established that X-ray irradiation of the crystals results in “radiation annealing” of TGS + Cr3+ crystals, which increases their permittivity and diminishes diffusion of the phase transition. 相似文献
14.
Ambrose Rajkumar Maridass S. Stanly John Xavier L. Priya S. Anbarasu P. K. Bajbai Shiva Poojan Patel 《Molecular Crystals and Liquid Crystals》2018,664(1):195-217
2-amino-5-nitropyridinium hydrogen oxalate (2A5NPHO) was grown using slow evaporation and bulk crystal of 2A5NPHO was harvested from Assembled Temperature Reduction (ATR) method. Cut and polished crystal was irradiated using Au3+ ion with various fluences. Electronic loss, nuclear energy loss and penetration depth were calculated using SRIM software. It was observed in X- ray pattern that intensity of peak was reduced. Intensity of peak decreased with increase of ion fluencies from 1013 ions/cm2 to 1014 ions/cm2. Optical properties were measured using UV-Vis spectrometer. The increase of absorption was due to excited electrons which were formed by vacancies and formation of additional defects centres. Energy band gap of irradiated crystals increased with increase of ion fluence. Energy band gap of irradiated crystals were 3.39 eV, 3.42 eV, and 3.4 eV for 1013 ions/cm2, 5 × 1013 ions/cm2 and 1014 ions/cm2 respectively and increase of band gap was due to the increase of forbidden gap. Microhardness was calculated using Vicker's Hardness tester. Increase of microhardness in irradiation crystal was due to increase of high density lattice defects produced by Au3+ of 10.8 MeV. Electrical property was calculated using dielectric constant. Increase of dielectric constant was due to large polarization which caused by disorderness and rich defects in the crystalline surface. Decrease of intensity peak in fluorescence was due to transition of excited electron to intermediated energy levels from excited state which converted into vibrational energy of lattice atoms (phonon). Morphology of irradiated crystal was seen using scanning electron microscope (SEM). It was observed from the SEM image that surface of crystal was heavily damaged. It was also noticed that the thermal stability of the irradiated single crystal increased with increase of ion fluences. Impedance of irradiated crystal was measured. The bulk resistance and grain boundary resistance also were calculated. 相似文献
15.
Amorphous films of Sb1?xTex, where 0.11 ? x ? 0.86, have been prepared by coevaporation. Crystallization temperatures occur near room temperature for all compositions and appear to depend on film thickness. The optical and transport properties have been investigated as a function of temperature. Optical band gaps at room temperature, Eg, ranged between 0.3 and 0.7 eV and decreased non-linearly with temperature. For the composition Sb2Te3, Eg ≈ 0.7 eV, in contrast to the semimetallic character of the crystalline form. All compositions were p-type with the Fermi level close to the middle of the gap. The results have been interpreted in terms of the chemical bonding. 相似文献
16.
The optical phonons at k = 0 of TlSbS2, TlSbSe2, and Tl3SbS3 have been investigated by infrared reflectivity measurements from 50 to 4000 cm−1 at 300 K. The factor group analysis of vibrational modes of TlSbS2 and Tl3SbS3 crystal lattices has been made. The dielectric constant dispersion for E ‖ a and E ‖ b has been determined by classical dispersion relations. The Szigeti effective charges, the Born dynamic effective charge, and the Tl, Sb, S (Se) relative ion charges were calculated in dependence on the polarization of the incident light. 相似文献
17.
T. Raghavendra Rao Ch. Rama Krishna R. Ramesh Raju R.V.S.S.N. Ravikumar 《Journal of Non》2011,357(18):3373-3380
The physical and structural properties of Co2+ doped 20ZnO + xLi2O + (30 − x)Na2O + 50B2O3 (5 ≤ × ≤ 25) (ZLNB) glasses have been studied and correlated. The physical and structural parameters of all the glasses are evaluated and a non-linear behavior is observed. No sharp peaks are observed in XRD patterns of the glass samples which confirm the amorphous nature. FT-IR spectra of ZLNB glasses reveal diborate units in borate network. The optical absorption spectra suggest the site symmetry of Co2+ in the glasses is near octahedral. Crystal field and inter-electronic repulsion parameters are also evaluated. The optical band gap and Urbach energies exhibit the mixed alkali effect. All the samples are found to be strong and stable in structure with low values of Urbach energy which lie between 0.027 eV and 0.039 eV. The correlation between densities and Urbach energies of Co2+ doped ZLNB glasses with respect to Li2O content suggest a changeover conduction mechanism from electronic to ionic, with a diffusivity crossover point at x = 15 mol%. 相似文献
18.
The optical properties of the Ga0.75In0.25Se crystals have been investigated by means of transmission and reflection measurements in the wavelength range of 380–1100 nm. The analysis of the results performed at room temperature revealed the presence of optical indirect transtions with band gap energy of 1.89 eV. The variation of the band gap energy as a function of temperature was also studied in the temperature range of 10–300 K. The rate of change of band gap energy (γ = –6.2 × 10–4 eV/K) and absolute zero value of the band gap (Egi(0) = 2.01 eV) were reported. The wavelength dependence of the refractive index was analyzed using Wemple and DiDomenico, Sellmeier and Cauchy models to find the oscillator energy, dispersion energy, oscillator strength and zero‐frequency refractive index values. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
F.P Koffyberg 《Journal of Non》1978,28(2):241-248
The refractive index, optical absorption coefficient α and the thermomodulated absorption dα/dT have been measured on 70% TiO2?30% SiO2 glasses with up to 8% Ti3+. The direct absorption data show intense ligand field absorption at photon energies hν = 1.9 and 3.0 eV, arising from Ti3+ in a distorted octahedral environment. In the bandgap region at 3.5 eV α obey αhν ~ (hν ? Eg)2; it is qualitatively different from the bandgap absorption in crystalline TiO2. The da/dT spectra show peaks in the bandgap region and at 1.1 eV in the near IR. This last peak is attributed to absorption by small polarons, and its line shape is compared with theoretical predictions. 相似文献
20.
N. M. Gasanly 《Crystal Research and Technology》2009,44(3):322-326
The optical properties of Tl2InGaSe4 layered single crystals have been studied through the transmission and reflection measurements in the wavelength range of 500‐1100 nm. The analysis of room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.86 and 2.05 eV, respectively. Transmission measurements carried out in the temperature range of 10‐300 K revealed that the rate of change of the indirect band gap with temperature is γ = – 4.4 × 10‐4 eV/K. The absolute zero value of the band gap energy was obtained as Egi(0) = 1.95 eV. The dispersion of the refractive index is discussed in terms of the single oscillator model. The refractive index dispersion parameters: oscillator wavelength and strength were found to be 2.53 × 10–7 m and 9.64 × 1013 m–2, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献