Optical Absorption Of Single Crystals Research Articles

Effect of the Addition of Silicon on the Properties of Germanium Single Crystals for IR Optics

Homogeneous Sb-doped single crystals of Ge–Si solid solutions are grown with a silicon content of 0.2 to 0.8 at %. The optical absorption of single crystals with a resistivity of (2–3) Ω cm is studied by IR Fourier spectroscopy at a wavelength of 10.6 μm in the temperature range from 25 to 60°C. It is found that the introduction of silicon into antimony-doped germanium improves the temperature stability of the optical properties of the crystals.

Влияние добавок кремния на свойства монокристаллов германия для инфракрасной оптики

AbstractHomogeneous Sb-doped single crystals of Ge–Si solid solutions are grown with a silicon content of 0.2 to 0.8 at %. The optical absorption of single crystals with a resistivity of (2–3) Ω cm is studied by IR Fourier spectroscopy at a wavelength of 10.6 μm in the temperature range from 25 to 60°C. It is found that the introduction of silicon into antimony-doped germanium improves the temperature stability of the optical properties of the crystals.

Band gap in tungsten sulphoselenide single crystals determined by the optical absorption method

Optical absorption in single crystals of tungsten sulphoselenides has been measured at room temperature with the incident light beam normal to the basal plane, i.e. along c-axis of the grown crystal flakes. Results have been analysed on basis of two-dimensional (2D) and three-dimensional models (3D). Absorption near the fundamental edge was found to be due to indirect allowed transition on the basis of (3D) model and due to indirect forbidden transition on the basis of a (2D) model. Both transitions involve two phonons. The energy gaps and phonon energies have been estimated. The indirect and direct band gaps of WS x Se 2− x vary smoothly with the S/Se composition x, indicating that the nature of band edges is similar for WSe 2, WS 2 and compounds of intermediate composition. The dependence of band gaps on sulphur/selenium content in WS x Se 2− x has been adequately explained on the basis of band structure calculations reported in the literature.

Optical band gap in tungsten diselenide single crystals intercalated by indium

Optical absorption in single crystals of In x WSe 2 ( x=0, 0.33, 0.50) has been measured at room temperature near the fundamental absorption edge. Results have been analyzed on the basis of two- and three-dimensional models. Both direct and indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons involved in the process. The direct and indirect energy gaps and phonon energies for all the crystals have been estimated. The three-dimensional model and not the two-dimensional model could be used to describe the optical properties of In x WSe 2 single crystals.

Optical Absorption of Single Crystals of Y3Al5O12and Y3Al5O12:Nd3+in the UV Fundamental Absorption Edge Region

Optical absorption curves for nominally pure and Ce 3+ doped single crystals of Y 3 Al 5 O 12 (YAG) have been measured in the region of 5 eV–7 eV at 292 K, 78 K and 10 K. The parameters of the Urbach rule have been determined referring to those optical absorption curves which are believed to be the fundamental absorption tail of YAG single crystals at these temperatures, respectively. Optical absorption measurements on single crystals of YAG:Nd 3+ (the concentration [Nd 3+ ] L being 0.60 atm.%) have disclosed strong absorption spectra consisting of at least five Gaussian bands in the region of 5.0 eV–7.0 eV at 292 K and 78 K. These spectra have been interpreted to originate from the interconfigurational transitions 4 f 3 →4 f 2 5 d of Nd 3+ in YAG.

Pressure dependence of deep level transitions in AgGaSe2

Polarized optical absorption in single crystals of AgGaSe2 has been measured as a function of hydrostatic pressure. Two polarized absorption peaks due to defects are reported. The pressure dependence of these peaks suggests that they are due to deep centers. These deep center absorption peaks merged into the fundamental absorption edge under high pressure.

Impurity optical absorption spectra of ZnGa 2Se 4:Ni 2+ single crystals

The optical absorption of single crystals of ZnGa 2Se 4:Ni 2+ grown by the chemical transport reaction method was investigated in the temperature region 20–300 K. In the single crystals the impurity optical absorption peaks due to the transitions 3 T 1( 3 F) → 3 T 2( 3 F), 3 T 1( 3 F) → 3 A 2( 3 F) and 3 T 1( 3 F) → 3 T 1( 3 P) of the Ni 2+ ions sited in the host lattice of the ZnGa 2Se 4 single crystal with Td symmetry appeared at 4444, 7874 and 11 600 cm −1, respectively. The crystal-field parameter and the Racah parameter were given by Dq = 340 cm −1 and B = 615 cm −1, respectively. The peak due to the transition 3 T 1( 3 F) → 3 T 1( 3 P) split into four levels by first order spin-orbit-coupling effects of Ni 2+ ions in the lower temperature below 150 K. The spin-orbit-coupling parameter was found to be λ = −400 cm −1.

Optical characterization of CuWO 4 single crystals

The optical absorption in single crystals of CuWO 4 has been studied at room temperature in the wavelength range 300–2000 nm. Crystalline samples suitable for optical measurements were prepared by the flux method. Optical absorption studies indicate a shoulder in the absorption edge akin to the transition from the valence to the conduction band.

Optical absorption in tin monoselenide single crystal

Optical absorption in single crystals of tin monoselenide has been measured at room temperature with plane polarized light near the fundamental absorption edge. The electric field of the incident light was oriented parallel to the a- and b-crystallographic axes in the plane of cleavage. Results have been analyzed on basis of two- and three-dimensional models. Absorption near the fundamental edge was found to be due to indirect forbidden transition with two phonons involved in the process. The energy gap and phonon energies were found to be 0.948 eV and 54 and 21 meV for the a-axis and 0.902 eV and 41 and 20meV for the b-axis. The two-dimensional model gave results similar to those obtained from the three-dimensional model and could thus be used to describe the main optical properties of SnSe single crystal.

Optical absorption edge in SnS

Optical absorption in single crystals of tin sulfide has been studied at many temperatures between 100 and 300 °K, in the wavelength range 2·2–0·8 μ. From the interference fringe patterns the absorption coefficient, reflection coefficient and index of refraction as a function of wavelength were determined for two light polarizations ( ε∥ a and ε∥ b). From an analysis of the data, indirect band gaps of 1·142 and 1·095 eV were found for the two directions of polarization. Also it was found that the phonon assisted transitions required the participation of two phonons at different energy thresholds with energies 0·033 or 0·038 eV and 0·082 or 0·113 eV, with reference to the two axis. The temperature dependence of the indirect band gap for each direction of light polarization is linear with a slope −4·05 × 10 −3eV and −4·37 × 10 −3 eV respectively.

Study of zirconium dioxide white pigment for space environment.

Abstract : The properties of zirconium dioxide as a stable white pigment (low alpha/epsilon) for space application are investigated. First, the optical absorption of single crystals is studied, leading to the conclusion that a high degree of purity, except for hafnium, is essential for stable white pigment applications. A subsequent pigment preparation study and irradiation experiments with UV and 3-keV protons are described. The ZrO coatings initially have alpha < 0.11 and epsilon = 0.9. Overall radiation stability (UV and proton) is shown to be binder-dependent, with potassium silicate more stable than silicones. Potassium silicate coatings show Delta alpha = 0.06 after 2400 UV equivalent solar hours, and Delta alpha = 0.01 after irradiation with 3-keV H(+) and H2(+) to a fluence of 10 to the 16th particles/sq cm. (Author)

The optical absorption edge of barium titanate

The optical absorption of single crystals of barium titanate has been measured in the region of the fundamental absorption edge. Results obtained on crystals after successive reductions in thickness allowed the true absorption coefficient to be calculated. Results confirm the direct transition at 305 eV and indicate a further transition at 263 eV which could be attributed to an indirect process.

Studies of the Optical and Infrared Absorption Spectra of Rutile Single Crystals

The optical absorption of single crystals of synthetic rutile was investigated in the spectral range 1200 to 25 000 cm−1 from room temperature to 1000°C. The electronic absorption exhibits dichroic behavior. The edge moves toward lower energies as temperature is increased, with the shift depending upon the absorption coefficient; for a decadic absorption coefficient α′ of 400 cm−1, the shift is −7.1×10−4 ev/°K, while at 1 cm−1 it is −9.5×10−4 ev/°K. The broad band in the region of 6850 cm−1 which occurs in reduced rutile does not appear in fully oxidized rutile, even at high temperatures. At high temperatures an additional wavelength-independent absorption appears which can be correlated in good agreement with dc conductivity by applying the Drude-Zener theory of free carrier absorption. New bands in the 3300 cm−1 region are shown to stem from O–H valence vibrations. The main bands are unusually sharp, with peaks at 3277 and 3322 cm−1 and half-widths of 28 and 13 cm−1. A satellite structure of combination and difference bands was also detected. Deuterium substitution produces an absorption band at 2442 cm−1. The entire structure shows a marked dependence of the absorption on the polarization direction of the light. Some evidence is presented that these O–H groups cause a dielectric dispersion.

Z-centres in Sodium Chloride containing Calcium

The optical absorption of single crystals of sodium chloride containing calcium as impurity has been measured. Results are given which show a new band at 345 mμ and from measurements of the bandwidth of the F-band it is deduced that the Z1-band is present in specimens, x-ray coloured, at room temperature. The growth of the Z-bands on bleaching in samples containing differing amounts of calcium impurity and the effect of quenching was also studied. Rate equations are used to discuss the coloration of NaCl and are also applied to the complex (Ca2+. plus sign in box. 2plus sign in box minus sign in box) to explain the coloration of the crystals containing Ca2+.