IR absorption and Raman spectra of single crystals of stable germanium isotopes

The Raman and IR absorption spectra of single crystals of germanium isotopes ⁷²Ge, ⁷³Ge, ⁷⁴Ge, and ⁷⁶Ge in the region of phonon absorption and interband electronic transitions are studied at room temperature. The dependence of the Raman peak position on the atomic mass has the form ν ~ M^–1/2. The shifts of the phonon absorption peaks of individual isotopes with respect to germanium of natural isotopic composition ^natGe are determined. With increasing average atomic mass of germanium, these peaks shift to longer wavelengths. In the region of interband electronic transitions, the intrinsic absorption edge of ⁷⁶Ge is observed to shift by 1 meV to higher energies with respect to Ge of natural isotopic composition. For isotopes with atomic masses close to that of natural germanium (⁷²Ge,⁷³Ge, ⁷⁴Ge), we found no significant difference in the band gap width at room temperature.     

Investigation on trap distribution and photoelectronic effect due to UV,IR and visible light excitation in self-activated zns crystals

Photoelectronic effects in IR sensitive ZnS crystals are found for IR, UV and visible light excitations. The transient rise characteristic of UV excited photoluminescence (UPL) saturates faster than UV produced photoconductivity (UPC). The UPC shows a typical S-shaped rise curve for any 365 run excitation irradiance and temperature. Simultaneously measured transient behaviors of IR induced photoconductivity (INP) and IR stimulated luminescence (STL) have a strong IR excitation intensity dependence for λ_IR = 2.5?4.6 microm. A unique phenomenon, quick rise followed by quick decay during the initial 20 msec, is found in INP before reaching final maximum but is not observed in STL. During UV steady irradiation, additional photoconductivity and luminescence are quickly induced by an abrupt IR excitation of 2.5 microm. Then, the photoconductivity reaches a new steady state level below UPC steady state. However, the luminescence sets the same UPL steady state level. This means that photoconductivity exhibits an IR optical quenching but not stimulation, while neither optical quenching nor stimulation is found in luminescence. It is also possible to quench the UPC response with visible light excitation at 570 nm. These observations support the previously reported discussion that IR absorbing impurity centers and shallow traps, including recombination (or luminescence) centers must be involved in IR stimulable ZnS crystals. They also indicate the presence of deep trap centers for E_T ≈ 2.18 eV, which have a strong role in slow UPC rise.     

Upconversion of IR radiation into the visible and UV ranges

A review of theoretical and experimental results on the upconversion of IR radiation due to resonant nonlinear phenomena in metal vapors is presented. Various experimental schematics providing high quantum conversion efficiency and the feasibility of converting an arbitrary IR wavelength are discussed.     

Effect of neutron irradiation on the IR absorption spectra of cupric oxide single crystals

A strong increase of the absorption coefficient with photon energy increasing from 0.1 to 1.0 eV is observed in the spectra of CuO single crystals irradiated with neutrons to a fluence of 5×10¹⁸ cm⁻². The difference of the absorption coefficients before and after irradiation depends on the wavelength as λ⁻². The effect of neutron irradiation on CuO is qualitatively similar to that of neutrons on other semiconductors (for example, GaAs) and differs from that obtained by irradiating CuO with charged particles. Zh. Tekh. Fiz. 69, 98–99 (December 1999)     

Raman light scattering in sodium nitrite crystals

Raman light scattering spectra of a ferroelectric sodium nitrite crystal is studied in the lattice mode region as the temperature is lowered from room temperature to 123 K. The existence of a Raman satellite corresponding to the soft lattice mode, i.e., transverse polar vibration responsible for the ferroelectric phase transition, is established for the first time. It is found that the intensity of the Raman scattering by the pseudo-scalar low-frequency A ₂ mode exceeds the intensity of other lattice variations by an order of magnitude.     

The optical and paramagnetic absorption spectra of MgO:Mn single crystals irradiated in a reactor

The optical and paramagnetic absorption spectra of MgO:Mn crystals of different origin, irradiated in a reactor, have been investigated. It is found that, in spite of only a small amount of Mn²⁺ impurity ions in the investigated crystals, their influence on the efficiency of formation and accumulation of F⁺-centers is dominant. The dependence of the number of F⁺-centers both on irradiation dose and on manganese concentration is studied.     

Computer programs for processing of UV and visible absorption spectra

A mathematical method for calculation of the stability constants of complexes by spectrophotometric data is represented. The program algorithm SQCONS is developed based on the method of nonlinear squares. As a test example, a calculation of the constant and the molar coefficients of extinction of the monosulfate complex CuSO ₄ ⁰ is presented. Institute of Mineralogy and Petrography of the Siberian Division of the Russian Academy of Sciences, 3, Universitetskii Ave., Novosibirsk, 630090, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 581–586, July–August, 1998.     

Strong UV absorption and visible luminescence in ytterbium-doped aluminosilicate glass under UV excitation

A broad visible luminescence band and characteristic IR luminescence of Yb(3+) ions are observed under UV excitation in ytterbium-doped aluminosilicate glass. Samples made under both oxidizing and reducing conditions are analyzed. A strong charge-transfer absorption band in the UV range is observed for glass samples containing ytterbium. Additional absorption bands are observed for the sample made under reducing conditions, which are associated with f-d transitions of divalent ytterbium. The visible luminescence band is attributed to 5d-4f emission from Yb(2+) ions, and the IR luminescence is concluded to originate from a relaxed charge-transfer transition. The findings are important to explain induced optical losses (photodarkening) in high-power fiber lasers.     

Laser removal of copper particles from silicon wafers using UV, visible and IR radiation

Laser removal of small copper particles from silicon wafer surfaces was carried out using Nd:YAG laser radiation from near-infrared (1064 nm) through visible (532 nm) to ultraviolet (266 nm). It has been found that both 266 nm and 532 nm are successful in removing the particles from the surface whereas 1064 nm was shown to be ineffective in the removal of particles. The damage-threshold laser fluence at 266 nm was much higher than other wavelengths which provides a much wider regime for safe cleaning of the surface without causing any substrate damage. The cleaning efficiency was increased with a shorter wavelength. The effect of laser wavelength in the removal process is discussed by considering the adhesion force of the particle on the surface and the laser-induced cleaning forces for the three wavelengths. Received: 31 May 2000 / Accepted: 14 July 2000 / Published online: 20 June 2001     

IR photoconductivity of C60 fullerene single crystals

The photoconductivity in the range 0.3–0.9 eV was investigated in a high-quality C₆₀ fullerene single crystal. It was concluded that the crystal investigated is an extrinsic semiconductor. Fiz. Tverd. Tela (St. Petersburg) 41, 1113–1114 (June 1999)     

Optical absorption and thermoluminescence of high a.c. field treated and X-ray irradiated potassium chloride single crystals

Optical absorption and thermoluminescence (TL) output measurements were made on high a.c. field treated and X-ray irradiated KCl single crystals. A substantial enhancement both in F-band peak absorption as well as in TL output was observed.     

Photoluminescence, optical absorption and XRD studies on X-ray irradiated terbium doped KBr crystals

This paper reports the optical absorption, photoluminescence (PL), XRD, SEM studies made on KBr:Tb³⁺ crystals. The integrated light intensity is enhanced by about two orders of magnitude as compared to the undoped samples in spite of some OH^- present in the samples. PL of these crystals exhibits characteristic Tb³⁺ emissions due to transitions from the ⁵D₃ to ⁵D₄ levels to various levels of the ⁷F septet on F-bleaching X-ray irradiated crystals Z₃ centers are observed. The bands observed in the emission spectra of Tb³⁺ doped KBr are found to be shifted to higher wavelength. The stokes-shift of KBr:Tb³⁺ is determined and it is found to have a large value. The XRD studies have been made to determine the crystalline structure of KBr and KBr:Tb³⁺ and also the Miller indices. The SEM studies made reveal the presence of microcrystalline structure.     

Raman scattering in sodium nitrite crystals near the phase transition

Optical Raman spectra of a ferroelectric sodium nitrite crystal have been detected in a wide spectrum range at various temperatures, including the region of the ferroelectric phase transition. A manifestation of a transverse soft polar mode of the A ₁(z) type responsible for the ferroelectric phase transition has been discovered in the spectrum at room temperature. This mode has been found to become overdamped even far from the ferroelectric phase transition temperature. This mode also appears as a central peak under heating. It has been found that the pseudoscalar mode of the A ₂ type has the highest intensity in the Raman spectrum of sodium nitrite. The frequency corresponding to the maximum intensity of this mode in the Raman spectrum varies from 130 cm^–1 at 123 K to 106 cm^–1 at T = 513 K. A fair agreement of the experimental data for the A ₁(z) mode with the Lyddane–Sachs–Teller relation has been established. The polariton curves for the A ₁(z) polar mode and the dispersion curves for axinons has been plotted.     

Structural,electrical and optical properties of gamma irradiated methyl para-hydroxy benzoate single crystals

ABSTRACT

Nonlinear optical materials (NLO) have been garnering attention due to their role in optical data storage, optical communication and laser technology. Organic crystals have emerged as an extremely important class of NLO materials, since their NLO properties compare very well with traditional inorganic NLO materials like KCl, LiNbO₃, KDP (potassium dihydrogen phosphate), etc. They offer the additional advantage that they can be grown relatively inexpensively from solution close to room temperature, unlike the inorganic NLO materials which are grown from high temperature melts. In the present work, organic transparent single crystals of methyl para-hydroxy benzoate (MHB) were grown by slow evaporation solution growth technique (SEST) from aqueous solution at room temperature. The changes in structural, electrical and optical properties of gamma irradiated MHB single crystals were studied using X-ray diffraction (XRD), UV–Visible absorption spectroscopy, Photo-luminescence (PL), Fourier transform infrared (FTIR) spectroscopy and AC conductivity measurements at room temperature. The polished MHB single crystals were irradiated with gamma rays of doses 10 and 15 kilogray (kGy). From the XRD analysis, it was observed that gamma irradiation for these doses drastically decreases the crystallinity. The optical absorption constants were examined by UV-Visible absorption spectroscopy, measured over the wavelength range of 200–800?nm, at normal incidence. The optical band gap as estimated from the Tauc plot ((αhν)² vs hν) was found to be reduced with increasing gamma irradiation doses. PL spectra showed emission at wavelengths of 361?nm (3.43?eV) and 452?nm (2.74?eV), with enhanced intensities for the irradiated crystals. FTIR spectroscopy was utilised to identify the functional groups of MHB and indicated the rupture of specific types of bonds with gamma irradiation. Apart from that, the enhancement of AC conductivity with gamma irradiation was also observed for the gamma irradiated crystals.     

Defect-induced magnetism in neutron irradiated 6H-SiC single crystals

Defect-induced magnetism is firstly observed in neutron irradiated SiC single crystals. We demonstrated that the intentionally created defects dominated by divacancies (V(Si)V(C)) are responsible for the observed magnetism. First-principles calculations revealed that defect states favor the formation of local moments and the extended tails of defect wave functions make long-range spin couplings possible. Our results confirm the existence of defect-induced magnetism, implying the possibility of tuning the magnetism of wide band-gap semiconductors by defect engineering.     

IR absorption spectra of molecular anions in CsI-CO3 and CsI-Tl,CO3 crystals

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 1, pp. 44–47, January, 1990.