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1.
The photoinduced optical absorption α of doped yttrium iron garnets (YIG) is investigated. It is found that the optical absorption α at a wavelength of 1.1 μm depends on the wavelength of irradiating light in the range 0.6–1.9 μm. It is demonstrated that, in the Y3Fe5O12 crystal with an acceptor Ba impurity, the photoinduced increase in α is due to the formation of Fe4+ ions in octahedral sites. The charge transfer occurs through photoexcitation of the 6 A 1g (6 S) → 4 T 1g (4 G) and 6 A 1g (6 S) → 4 T 2g (4 G) transitions of octahedral Fe3+ ions. In the crystal with a donor Si impurity, the increase in α is caused by the formation of Fe2+ ions upon photoionization of silicon. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 7, 2001, pp. 1233–1235. Original Russian Text Copyright ? 2001 by Doroshenko, Nadezhdin.  相似文献   

2.
Fe2+ site occupancy in iron garnets is investigated by means of optical absorption and magnetic circular dichroism. In particular measurements are carried out on bulk single crystals of yttrium iron garnet (YIG) doped with Si4+, Nb5+, Sn4+, Zr4+, Ti4+ and Th4+. The results are discussed in the light of the recent discovery of tetrahedral Fe2+ in Nb-doped YIG. We find that, in general, Fe2+ occupies both octahedral and tetrahedral sites, the actual distribution being related to site occupancy of the donor centers. This correlation may be relaxed by photoinduced charge transfer between iron sites, at low temperatures. Contrary to recent attributions, no dodecahedral component is found in the infrared spectra above 1 μm wavelength.  相似文献   

3.
This paper is concerned with the preparation and characterization of cerium-substituted yttrium iron garnets, which are known to be oxides having a large Faraday rotation effect. Using the improved flux method we successfully grew bulk single crystals of iron garnet doped with Ce3+ ions with maximum substitutions up to 0.349. Here we investigate different solution compositions for maximum Ce3+ substitution. The Faraday rotation and optical absorption spectra were measured in the near infrared region for different Ce3+ ion substituted iron garnets. The specific Faraday rotation of Ce0.349Eu0.195Y2.456Fe5O12 was found to be 1430 deg/cm at a wavelength of 780 nm and –1280 deg/cm at 1150 nm. The Ce substitution prominently enhances the Faraday rotation effect, and Yb3+ and Eu3+ ions substituted for Y3+ in the dodecahedral sites of YIG can increase the concentration of Ce3+ ions, depressing the formation of nonmagnetic Ce4+ ions by charge compensation. Received: 24 January 2001 / Accepted: 2 March 2001 / Published online: 27 June 2001  相似文献   

4.
Experimental results for free carrier absorption at room temperature in lightly doped samples of n-type CdTe, including the λ3 dependence of the absorption coefficient on the photon wavelength, can be satisfactorily accounted for in terms of polar optical mode scattering with a very small contribution by impurity scattering. Use is made of the quantum theory of free carrier absorption initially developed for direct gap III–V semiconducting compounds, which utilizes the Kane band structure and includes nonparabolicity, arbitrary spin-orbit splitting values, overlap wave function factors, and intermediate states in other bands.  相似文献   

5.
Calculations of the Faraday rotation (FR) and magnetic circular dichroism spectra in the wavelength region between 300 nm and 650 nm caused by the Ce3+ ions in the Ce substituted aluminium garnets (YAG) based on the quantum theory are presented. The Faraday effect contributed by the Ce3+ ions is caused mainly by the intraionic electrical dipole transitions between the 4f and 5d configurations. The effect of the crystal field (CF) and spin orbit coupling on the Faraday effect has been discussed. The CF upon the Ce3+ ions doped in garnets depends strongly on the nature of the next-nearest neighbors. The CF upon the Ce3+ ions in YAG is weaker than that in yttrium iron garnets (YIG). Therefore, compared with Ce: YIG, the anomalous rotatory dispersions occur at higher frequencies. The shape of the FR spectrum caused by the Ce3+ ions in YAG is different from that caused by the Ce3+ ions in YIG. An explanation of this difference is given. The influence of the mixing of different multiplets of the ground configuration on the Faraday effect is discussed. Such mixing is one of the causes which make the magneto-optical coefficient vary with temperature.  相似文献   

6.
崔昊杨  李志锋  马法君  陈效双  陆卫 《物理学报》2010,59(10):7055-7059
利用皮秒Nd:YAG脉冲激光器作为激发光源,测量出光子能量介于1.36 μm (0.912 eV)—1.80 μm (0.689 eV)之间的硅间接跃迁双光子吸收系数谱.尽管此波段范围内的激光光子能量小于硅间接带隙,但当激光辐照在硅基光电二极管受光面时,在二极管两电极端仍然探测到了显著的脉冲光伏信号.光伏信号峰值强度与入射光强呈二次幂函数关系,表明其是双光子吸收过程.采用pn结等效结电容充放电模型,将光伏响应信号峰值与入射光强相关联,从中提取出硅的间接跃迁双光子吸收系数,改变入射波长得到系数谱.研究表明:  相似文献   

7.
The attenuation of the anisotropy of the γ-γ angular correlation for a rare-earth ion in magnetic iron and non-magnetic aluminum rare-earth garnets is governed by the static hyperfine electric field gradient (EFG) produced by the surrounding ions and by the static and fluctuating hyperfine magnetic fields produced by the 4f electrons of the ion. The latter effect depends upon the correlation time (τc) of the 4f electrons which, in turn, is determined by the interaction of the ionic spin with lattice vibrations and other magnetic ions. In an attempt to determine the significance of spin-spin relaxation on τc, perturbed angular correlation (PAC) measurements were performed on the S-state ion154Gd3+ because spin-lattice interactions were expected to be small. The time-integral attenuation coefficients of the 1274/123 keV γ-γ cascade in154Gd were measured in the temperature region 4.2–650 K for154Gd3+ incorporated in GdAlG, GdIG, YAlG, and YIG. Rotation measurements were also made on the same cascade in the iron garnets at room temperature with an applied magnetic field in the range 0–15 kg. Employing independent measurements and calculated estimates of the static hyperfine magnetic field and EFG, the observed data could be interpreted in terms of reasonable values of τc. The correlation times were found to range from about 0.13 ns in YIG to about 1.30 ns in YAlG with GdAlG having a value of approximately 0.71 ns. In the case of GdIG, a self-consistent analysis of the data required a value of the lattice EFG which was larger than that estimated from the nearest neighbor point-ion model. The correlation time in GdIG was then found to be the same as in YIG.  相似文献   

8.
The absorption constantK of amorphous As2S3 was determined at the absorption edge in the range 1 to 105 cm–1. It is shown that at low energy levels up to about 103 cm–1 K depends exponentially on the photon energy; at higher absorption levels the energy dependence ofK is quadratic. The significance of these results is discussed. When sulphur is added to As2S3 the absorption edge has similar properties but is shifted towards lower energies.  相似文献   

9.
A quantum mechanica treatment of the free carrier absorption by electrons in polar semiconductors has been constructed in terms of the Kane model. It takes into account overlap wavefunction factors, intermediate states in other bands, the finite optical phonon energy, and the effects of arbitrary spin orbit splitting on the electron energy and wavefunction. The scattering mechanisms considered include polar optical mode scattering, ionic scattering, piezoelectric and deformation coupled acoustic mode scattering, and electron-electron scattering.The theory, in the appropriate limits, applies to a wide range of photon energies, electron concentrations, and lattice temperatures. It relates the dominant scattering mechanism involved in the various limits to the characteristic behavior of the absorption coefficient as a function of the photon energy. In particular, the dominant scattering mechanism for small carrier concentrations is found to be polar optical mode scattering, which exhibits a λ3 dependence of the absorption coefficient times the index of refraction, (except at the lowest frequencies, where the expected λ2 dependence is obtained).Ionic, or impurity, scattering becomes important as the carrier concentration is increased, and the characteristic wavelength dependence of the electron cross section times the index of refraction varies from λ4 to λ3, and the absorption coefficient times the index of refraction from λ4 to λ2, depending on the ratio of the photon energy to the initial electron energies.Comparisons are made with the available data over a wide range of photon energies, temperatures, and electron concentrations, for the III–V compounds InSb, InAs, InP, and GaAs.  相似文献   

10.
The theory of optical absorption due to transitions between a valence band and a hydrogen-like local level associated with a conduction band is modified to permit an arbitrary power-law dependence of energy on the magnitude of the wave-vector of carriers in the valence band. The observed absorption for photon energies below 1.6 eV in the ferromagnetic semiconductor CdCr2Se4 is discussed in terms of a combination of two types of terms. The first type of absorption is due to transitions to a local level from a band with two branches, in each of which there is an energy region with a width of 0.28 eV or more beginning 0.10–0.16 eV from the band edge, in which the energy measured from some origin near but not necessarily equal to the band-edge is approximately proportional to (wave-vector)(13). The second type of absorption has a dependence on photon energy ?ω of the form (?ω ? E3)2, where E3 is a threshold energy probably connected with indirect transitions between bands as suggested by Sakai, Sugano and Okabe. After constraints on parameters appearing in the theory are imposed by use of results of these authors and of Shepherd, it is found that curves of Harbeke and Lehmann on optical absorption in CdCr2Se4 at 4.2, 78, 130 and 298 K in the photon-energy range 1.14–1.42 eV can be fitted to a mean accuracy of 3%, using an average of 3.75 adjustable parameters for each curve. The strength of the indirect band-to-band absorption does not have the temperature dependence expected for phonon-assisted indirect band-to-band transitions, but can be described by a term independent of temperature plus another term proportional to the square of the deviation of the magnetization from saturation. The fitting of the absorption curves requires that the ratio of the widths of the two branches of the bands varies from about 1.6 at low temperatures to 1.35 at 298 K and that the total width of the bands involved is less than 1 eV.  相似文献   

11.
Deep levels in iron-dopedp-type silicon are investigated by means of Deep Level Transient Spectroscopy (DLTS) and the Hall effect. Pairs of Fe with the acceptors B, Al, and Ga are observed at 0.1, 0.19, and 0.24 eV above the valence band edgeE v. For interstitial iron, (Fe i ), a level energy ofE v+0.39+-0.02 eV is obtained with DLTS after correction with a measured temperature dependence of the capture cross section. The Hall effect yieldsE v+0.37 eV for Fei. The annealing behavior of levels related to Fe is investigated up to 160 °C. Iron participates in at least four different types of impurity states: Fe i , Fe-acceptor pairs, precipitations (formed above 120 °C) and an additional electrically inactive state, which is formed at room temperature.  相似文献   

12.
The optical properties of EuGa2S4 and EuGa2S4:Co single crystals in a range of temperatures from 77 to 300 K are investigated. The single crystals are obtained by the Bridgman method and are characterized by tetragonal syngony. The behavior of the optical transitions in the photon energy range 1.70–2.45 eV and the temperature range 77–300 K is determined. It is established that in the energy range 1.77–1.90 eV absorption is associated with transitions of the Co2+ ion, while in the range 2.20–2.40 eV, with indirect allowed optical transitions.  相似文献   

13.
The optical absorption, emission and excitation spectra of Pr3+ ions in LiYF4 have been measured. Energy transfer is observed and an estimate of the energy transfer rate is made. The temperature dependence of the emission lifetimes for Pr3+ and Er3+ and the Judd-Ofelt theory were used to make this determination. The energy levels responsible for the various transitions have been assigned previously by Esterowitz et al. and the polarized optical absorption and emission data presented in this paper are in agreement with their excellent work.  相似文献   

14.
Considerable changes were observed in the X-ray diffraction pattern of ammonium zinc chloride after doping with Sr2+ in different concentrations and after irradiating with γ rays at different doses. The effect of γ-radiation and Sr2+ content on optical parameters of (NH4)2ZnCl4: x Sr2+ single crystals (x?=?0.00, 0.020, 0.039, 0.087 or 0.144?wt.%) has been investigated. The transmittance near the absorption edge of unirradiated crystals and crystals irradiated with different γ-doses has been measured, hence the absorption coefficient (α) was calculated. The values of α at room temperature increased under the influence of γ-irradiation. The rate by which α increases with photon energy just before the absorption edge is strongly inhibited by higher γ-doses. The type of intraband transition in (NH4)2ZnCl4: x Sr2+ single crystals was found to be of the allowed indirect transition, and γ-irradiation had no effect on the type of transition. The values of the optical energy gap (E g ) were calculated as a function of γ-dose. The effect of γ-irradiation was found to be more pronounced on samples doped with x?=?0.087 or 0.144?wt.% Sr2+. The results can be discussed on the basis of γ-irradiation-induced defects and Sr2+ concentration. A diagram representing probable transitions to the created bands due to irradiation could be constructed.  相似文献   

15.
The fluorescence of Mn2+ ion as impurity in CaCO3 has been investigated. Emission bands from the 4D(Eg), 4D(T2g) and 4G(T1g) levels have been observed. The analysis of excitation and emission spectra has allowed to obtain the values of field strength (Dq) for the excited energy levels of Mn2+ in CaCO3 lattice. The temperature dependence of excitation and emission spectra yield an activation energy for thermal quenching of luminescence very close to theoretical calculation. The behaviour of luminescence lifetime with temperature has also been obtained.  相似文献   

16.
We report the wavelength and temperature characteristics of novel Bi-substituted rare-earth iron garnet films grown on a YIG substrate by a modified liquid phase epitaxy (LPE) technique. The Faraday-rotation spectrum was measured by the magneto-optically modulated dual-frequency technique with the wavelength varied from 800 nm to 1700 nm. The resultant Bi0.37Yb2.63Fe5O12 (BiYbIG) LPE film/YIG crystal structure showed an increased Faraday-rotation coefficient due to Bi3+-ion doping on the dodecahedral sites of the iron garnet without increasing absorption loss; therefore, a good magneto-optical figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved (21.5 deg/dB and 30.2 deg/dB at 1300-nm and 1550-nm wavelengths, respectively, at room temperature). In addition, since the Yb3+ and Y3+ ions provide opposite contributions to the wavelength and temperature characteristics of the Faraday rotation, the resultant BiYbIG LPE film/YIG crystal structure showed a flat Faraday-rotation curve versus wavelength and temperature. The Faraday-rotation wavelength coefficient was reduced to 0.06 %/nm at 1550-nm wavelength. The Faraday-rotation temperature derivative was reduced to 0.006 deg/°C at 1300-nm wavelength and 0.007 deg/°C at 1550-nm wavelength, respectively. PACS 78.20.Ls; 81.15.Lm; 75.50.Gg  相似文献   

17.
The absorption spectra of Y3Ga5O12:(Fe3+), Y3Ga5O12:(Bi3+) and Y3Ga5O12:(Bi3+, Fe3+) are presented to 40,000 cm-1. Assignments are discussed and the transitions analysed in terms of their involvement in the large Faraday rotation observed in bismuth substituted iron garnets.  相似文献   

18.
Optical absorption in MnGaInS4 single crystals has been studied. Direct and indirect optical transitions are found to occur in the range of photon energies of 2.37–2.74 eV and in the temperature range of 83–270 K. The temperature dependence of the band gap has been determined; its temperature coefficients E gd and E gi are −5.06 × 10−4 and −5.35 × 10−4 eV/K, respectively. MnGaInS4 single crystals exhibit anisotropy in polarized light at the absorption edge; the nature of this anisotropy is explained.  相似文献   

19.
In this work, investigation of the spectroscopic parameters of the luminescence of Yb3+ ions in single crystalline films of Lu3Al5O12 and Y3Al5O12 garnets was performed using the synchrotron radiation excitation with the energy in the range of Yb3+ charge transitions (CT), exciton range and the onset of interband transitions of these garnets. The basic spectroscopic parameters of the Yb3+ CT luminescence in LuAG and YAG hosts were determined and summarized with taking into account the differences in the band gap structure of these garnets.  相似文献   

20.
Because of the need for tunable solid state lasers in the blue region of the spectrum, a number of recent studies have been on the optical properties of Eu2+ in various crystals lattices. The absorption and emission from Eu2+ ions in fluoride hosts arise from both 5d→4f and 4f→4f transitions. The absorption is in the ultra-violet and the emission is in the blue. The 4f-4f transitions are very sharp and are located around 360 nm. The 5d→4f emission bands at 405 nm and 525 nm are broad and host lattice dependent. We have studied the temperature dependence of the optical properties of RbMgF3:Eu2+ including absorption, emission, and excitation. In the case of the emission studies both temperature dependence and the lifetimes of the transitions have been measured. These transitions are discussed in detail.  相似文献   

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