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1.
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   

2.
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   

3.
BaFCl crystals have been grown using BaF2 and BaCl2 by flux technique. Glow curves, optical absorption, and TL emission spectra of x/r — irradiated crystals are studied. The results have been compared with those BaFCl crystals grown from NaF flux so as to study the effects of flux on these properties. It is found that crystals grown from BaF2 flux are relatively purer. An additional TL glow peak at 460 K, an optical absorption band at 775 nm and TL emission band at 485 nm have been obtained in the presently grown crystals. The additional glow peak, optical absorption band have been attributed to F(¯F) aggregate centers, whereas the 485 nm TL emission band to impurity centers.  相似文献   

4.
Potassium bismuth tungstate [KBi(WO4)2] single crystals with dimensions up to 20 mm × 15 mm × 15 mm have been successfully grown by using the top‐seeded solution growth technique and K2W2O7 as solvent. Experiments show that this crystal is unstable in a strong acid or alkali environment and has a blue fluorescence emission. The density, hardness, melting point, absorption edge, transparency range, prominent Raman shift frequency are 7.57 g/cm3, 238 kg/mm2, 800 °C, 380 nm, 400–5450 nm, 868 cm–1 respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
Organic optical material 4‐Aminopyridinium‐4‐nitro phenolate (4AP4NP) has been synthesized, and single crystals of size 20 x 14 x 6 mm3 have been grown from acetone solvent at room temperature by solvent evaporation technique. The grown crystals have been characterized by X‐ray diffraction to determine the cell parameters, and by FT‐IR technique to confirm the formation of the expected compound. The crystal belongs to monoclinic crystal system with space group P21/a.The structural perfection of the grown crystals has been analyzed by high‐resolution X‐ray diffraction (HRXRD) rocking curve measurements. The thermal stability of the compound has been determined by TG‐DTA curves. The transmittance of 4AP4NP has been used to determine the refractive index n; the extinction coefficient K and both the real εr and imaginary εi components of the dielectric constant as functions of photon energy. The optical band gap of 4AP4NP is 2.4 eV. The dielectric and mechanical behavior of the specimen was also studied. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
Potassium bismuth tungstate [KBi(WO4)2] single crystals have been grown by the top‐seeded solution growth technique. Bulk crystal with dimensions up to several centimeters is obtained for the first time. Several self‐flux systems have been used for the growth from the solution and the experiments using K2W2O7 as a solvent are detailed. Powder and single crystal X‐ray diffraction of this crystal are reported. The structure refinement shows that KBi(WO4)2 crystallizes in the monoclinic space group C2/c, with a=10.837(3), b=10.586(3), c=7.622(2)Å, β=130.860(3)°, V=661.4(3)Å3, and Z=4. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
Barium tungstate (BaWO4) single crystal has been grown using Czochralski technique. It belongs to the scheelite structure, forming the space group I 41/a at room temperature and the primitive cell contains two molecular units. The polarized Raman spectra were recorded by a micro‐Raman spectrophotometer system in the backscattering geometry. All the observed Raman modes were assigned. The Raman mode at 924 cm–1, which belongs to the totally symmetrical Ag optical modes, has the strongest intensity and its linewidth is 4.6 cm–1. The infrared active lattice vibrations have been studied, eight optical modes were observed and assigned. The ultraviolet absorption edge is at 256 nm and the optical transparency range is up to 2500 nm at room temperature. The energy gap Eg of this crystal was obtained from the optical transmission spectra. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

8.
KTiOPO4 single crystals of dimensions 34 × 15 × 15 mm3 have successfully been grown by Top Seeded Solution Growth (TSSG), using phosphate flux (K6P4O13), employing a home made vertical cylindrical three zone resistive heated furnace. Growth experiments were carried out with <001> seed orientation. A method to grow inclusion free crystal with less dislocation density is proposed, by employing cooling rate of 0.5‐2 K/day and rotation rate of 60‐30 rpm. UV‐VIS transmission studies were performed and the dependence of absorption coefficient with wavelength is discussed. SHG elements of dimension 8 × 7.5 × 7.5 mm3 were fabricated and conversion efficiency of 58 % was achieved without antireflection coating. Nature of ionic conductivity and ferroelectric phase transition behavior of KTP crystals along the crystallographic polar axis in the frequency range of 100 Hz – 10 MHz are discussed.  相似文献   

9.
Lithium tetraborate, Li2B4O7 (LTB) crystals were grown by Czochralski technique. It belongs to tetragonal system with lattice parameter a = b = 9.479 Å, c = 10.286 Å. Transmission range of this crystal is 170 nm – 3300 nm. This material has attracted much attention because of its application in higher harmonic generation of Nd:YAG laser and radiation dosimetry. The grown crystals were characterized for their optical inhomogeneity using etch pit study, hardness, conoscopy, interferometry, and UV‐VIS transmittance techniques. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
The optical properties of the TlInS2xSe2(1‐x)mixed crystals (0.25 ≤ x ≤ 1) have been investigated through the transmission and reflection measurements in the wavelength range of 400–1100 nm. The optical indirect band gap energies were determined by means of the analysis of the absorption data. It was found that the energy band gaps decrease with the increase of selenium atoms content in the TlInS2xSe2(1‐x)mixed crystals. The transmission measurements carried out in the temperature range of 10–300 K revealed that the rates of change of the indirect band gaps with temperature are γ = –9.2×10–4 eV/K, –6.1×10–4 eV/K, –4.7×10–4 eV/K and –5.6×10–4 eV/K for TlInS2, TlInS1.5Se0.5, TlInSSe and TlInS0.5Se1.5 crystals, respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

11.
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   

12.
4‐nitrophenol (4‐NP) single crystals have been grown by using slow evaporation and slow cooling techniques. A single crystal with size in the range of 7x3.4x1.8cm3 has been obtained by slow cooling method. The grown crystals have been subjected to various characterization studies. The powder XRD spectrum of 4‐NP reveals the good crystalline nature of the grown crystal. Single crystal XRD studies show that the crystal belongs to monoclinic system with cell parameters of a=6.09 Å, b=8.79 Å, c=11.61 Å, α=γ=90°, β=103.15°. The resultant FTIR spectrum confirms the various functional groups present in 4‐NP. Thermal analysis has been performed on the material to study the thermal stability of 4‐NP. The grown crystals belong to the category of soft materials as confirmed by Vickers Hardness tests. The optical transmiitance of 4‐NP single crystals has been measured from Vis‐IR spectroscopy study. The nonlinear optical properties have been analyzed by z‐scan technique and 4‐NP is found to be self defocusing because of its negative nonlinear refractive index. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

13.
Single crystals of ferroelectric succinic acid (SA) with very high degree of transparency were grown from aqueous solution by slow evaporation technique. Single crystal X‐ray diffraction analysis reveals that the crystal belongs to monoclinic system with the space group P21/c. Some physical parameters have been determined for grown crystal. The optical absorption study reveals the transparency of the crystal in the entire visible region and the cut off wave length was found to be 240 nm. The optical band gap is found to be 3.75 eV. The dependence of extinction coefficient (k) and refractive index (n) on the wavelength have also been reported. The presence of functional groups was determined qualitatively by using Fourier transform infrared spectrum (FTIR) from which force constant has been calculated. The dielectric constant was also studied as a function of frequency at room temperature and electrical conductivity has been calculated from the Cole‐Cole plot. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
The investigations on the formation of mixed crystals of ammonium dihydrogen orthophosphate (ADP) and potassium dihydrogen orthophosphate (KDP) i.e. potassium ammonium dihydrogen phosphate, K1‐x(NH4)xH2PO4 have been presented in this paper. Pure and mixed crystals of ADP and KDP have been grown by slow evaporation technique from the supersaturated solution at an ambient temperature 26±1 °C for ammonium concentration x in the range 0.0 ≤ x ≤ 1.0 in the case of mixed crystals. Crystal compositions were determined by flame atomic absorption spectroscopy and chemical analysis. The results of the X‐ray analysis of the grown crystals are also reported. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study the kinetic process of dehydration and the high temperature phase behaviour. DTA showed the distinct thermal events attributed to dehydration of ADP, KDP and K1‐x(NH4)xH2PO4. The results of thermal analysis and chemical analysis are consistent with each other. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

15.
KTP crystals have been grown by two nucleation techniques namely spontaneous nucleation in flux medium and nucleation on Pt rod using K6P4O13 flux.10 °C/h, 7 °C/h, 0.8 °C/h, 0.4 °C/h and 0.2 °C/h cooling rates were applied for spontaneous nucleation and crystals up to 15 × 7 × 4 mm3 in size were grown. 1 °C/h and 0.8 °C/h cooling rates were also used for nucleation on Pt rod and crystals up to 8 × 6 × 3 mm3 in size were grown. The effect of cooling rate on size, morphology and optical quality of grown crystals by both techniques were studied. For nucleation on Pt rod upper and lower rotation rates limits and an optimum rotation rate were distinguished for each cooling rate. Quality of the grown crystals by both techniques was characterized by optical transmission analysis.  相似文献   

16.
Zirconium‐doped KTiOPO4 (KTP) crystals were grown using a high temperature flux method in the K2O‐P2O5‐TiO2‐ZrF4 system. The dopant content in the single crystals with general composition KTi1‐xZrxOPO4 (where x = 0 – 0.026) strongly depends on zirconium concentration in the homogeneous melts. AES‐ICP method and X‐ray fluorescence analysis were used to determine the composition of the obtained crystals. Phase analyses of the products were performed using the powder XRD. The structures of KTiOPO4 containing different quantities of Zr were refined on the basis of single crystal XRD data. Applying ZrF4 precursor for zirconium injection into the flux allowed growing the zirconium‐doped KTP crystals at 930–750°C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

17.
The as‐grown surface and inner structures of undoped and Nd3+‐, Cr3+‐, V3+‐, Ce3+‐, Er3+ and Yb3+ – and (Er3+ + Yb3+) – doped yttrium aluminum borate (YAB) single crystals grown from (K2Mo3O10 + B2O3) flux by spontaneous crystallization or top seeded solution growth (TSSG) technique, were investigated using optical and scanning electron microscopic and analytic chemical methods. Fine and rough growth hillocks of dislocational origin, growth layers, traces of inner planar defects and foreign phase crystalline debris were found and analyzed on the as‐grown faces of crystals. Irregular grains and regular block structures and foreign phase inclusions were observed and studied in the interior of the crystals. The chemical compositions measured by energy dispersive X‐ray spectrometry on perfect and imperfect micro regions are compared with those obtained by flame atomic absorption spectrometry on bulk crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

18.
Photoluminescence spectra of Tl4GaIn3S8 layered crystals grown by Bridgman method have been studied in the wavelength region of 500–780 nm and in the temperature range of 26–130 K with extrinsic excitation source (λexc = 532 nm), and at T = 26 K with intrinsic excitation source (λexc = 406 nm). Three emission bands A, B and C centered at 514 nm (2.41 eV), 588 nm (2.11 eV) and 686 nm (1.81 eV), respectively, were observed for extrinsic excitation process. Variations in emission spectra have been studied as a function of excitation laser intensity in the 0.9‐183.0 mW cm–2 range for extrinsic excitation at T = 26 and 50 K. Radiative transitions from the donor levels located at 0.03 and 0.01 eV below the bottom of the conduction band to the acceptor levels located at 0.81 and 0.19 eV above the top of the valence band were proposed to be responsible for the observed A‐ and C‐bands. The anomalous temperature dependence of the B‐band peak energy was explained by configurational coordinate model. From X‐ray powder diffraction and energy dispersive spectroscopic analysis, the monoclinic unit cell parameters and compositional parameters of Tl4GaIn3S8 crystals were determined, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
Potassium holmium tungstate KHo(WO4)2 crystal, as other tungstates, shows the high temperature irreversible structural phase transition. Owing to this, KHo(WO4)2 single crystals were grown due to spontaneous crystallisation with use of the High Temperature Solution Growth technique, which allows to lower the temperature of crystallisation below the temperature of the phase transition. K2W2O7 was used as a solvent. It provides a very wide temperature range of crystallisation and does not introduce additional impurities into the melt. The starting flux contained 20 mol% of KHo(WO4)2 dissolved in K2W2O7. It was found that potassium holmium double tungstate is pleochroic. The two different optical spectra: one spectrum for electrical vector of linearly polarised light parallel to optical Y axis (main spectrum) and second one for electrical vector perpendicular to Y axis were measured.  相似文献   

20.
Optical absorption of tris thiourea zinc sulphate (ZTS) single crystals has been measured and its direct band gap was found to be 3.6 eV. Theoretical calculations were carried out to determine the linear optical constants such as extinction coefficient and refractive index. Further the optical nonlinearties of ZTS have been investigated by Z‐scan technique with He‐Ne laser at 632.8 nm. The nonlinear refractive index, absorption coefficient and third order susceptibility is found to be in the order of –5.36 ± 0.26 × 10–12 cm2/W, 4.24 ± 0.21 × 10–4 cm/W, 3.5 ± 0.17 × 10–4 esu respectively. Thus optical characterization of ZTS reveals the various industrial application oriented properties of the material. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

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