Temperature dependence of photoluminescence and electroluminescence of ZnS:Mn crystals

By means of comprehensive analysis of the temperature dependences of the photoluminescence for ZnS:Mn crystals, we have observed persistent changes in the intensity, shape, and position of the maximum in the emission spectrum associated with changes in the immediate environment of the manganese luminescence centers. We have also observed inflection points on the voltage vs. brightness characteristics of the samples, the position of which depends on the frequency of the exciting voltage and the temperature. The observed dependences are explained using concepts describing the mechanisms of pre-breakdown luminescence. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 631–636, September–October, 2006.     

Effect of surface fields on luminescence of ZnS and ZnO crystals

It is shown that changes in luminescence characteristics of zinc sulfide and oxide in the presence of external effects that alter the surface charge are associated with a change in the parameters of surface barriers and can be explained within the framework of a model that takes into account separation of recombining partners in the Schottky barriers. We suggest a barrier mechanism for the effect of the surface region of a crystal on experimentally measured luminescence parameters and show that errors occuring in the measurement of these parameters can reach 10% and greater, depending on the depth of penetration of light. Moscow State University of Railways, 15 Obraztsov Str., Moscow, 103055, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 804–808, November–December, 1999.     

Influence of an electric field and a high excitation density on the luminescence of epitaxial GaN films

The influence on the recombination luminescence spectra of a field applied to the Schottky barrier and a high excitation density GaN epitaxial films grown by metalorganic chemical-vapor deposition (MOCVD) is investigated. It is discovered that quenching of the luminescence takes place under a reverse bias, while an increase in its intensity occurs under a forward bias. The effect observed is attributed to thickness variation of the space-charge layer under the effects of the applied voltage. The appearance of a new band caused by exciton-exciton collisions is observed under the conditions of a high excitation density. Fiz. Tverd. Tela (St. Petersburg) 40, 936–937 (May 1998)     

Resonant-Optical Detection of Nuclear Magnetization in the Si/CaF<Subscript>2</Subscript> Nanostructure

We have considered theoretically the characteristic features of optical detection of nuclear magnetization in the Si/CaF₂ structure under the conditions of EPR and NMR by measuring luminescence polarization. We show that application of EPR makes it possible to detect weak nuclear fields, but the time of spin relaxation of electrons imposes its constraint. The application of NMR is limited by nuclear fields of no less than 15–20 Gs. The possibility of using optical NMR for direct measurement of the nuclear field from changes in the luminescence polarization spectrum is shown. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 644–649, September–October, 2005.     

Luminescence and Electrical Properties of CdS Films Doped with Potassium and Sodium

CdS films, both pure and doped with the alkali metals Na and K, with Cl and without it, obtained by the aerosol pyrolysis method from thiourea coordination compounds at a temperature of 250 to 500°C are investigated. The photoluminescence spectra and the dependence of the luminescence intensity on the duration of exposure of samples to a high-power UV radiation have been obtained. The doping of samples results in a tenfold increase in the intensity of the luminescence band in the visible spectrum range (650–850 nm) as compared to pure samples of CdS. Upon irradiation of samples by high-power UV radiation for 1 h, no noticeable change in the intensity of luminescence of CdS films was observed. This is indicative of the stability of the films under study against the action of UV radiation. The luminescent properties of the films, obtained pyrolytically using thiourea coordination complexes, are determined by the synthesis conditions as well as by the chemical nature of the original substances. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 509–513, July–August, 2005.     

Rotation of the polarization plane of waves in anisotropic media

Conditions under which rotation of the wave polarization plane is observed are formulated for anisotropic media with various symmetry types. The results may be of interest in solution of the inverse problem of constructing model geophysical media from an observed polarization plane rotation effect. Institute of Planetary Geophysics, Russian Academy of Sciences: Moscow Institute of Radioengineering, Electronics and Automation (Technical University); Moscow Academy of Instrumentation and Informatics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 82–89, May, 1996.     

Investigation of fatigue relaxation of luminescence in porous silicon by time-resolved spectroscopy

This paper describes the first investigations of how the intensities of various time-resolved components of the luminescence from porous silicon relax with time. A paradoxical correlation is observed between the macro-and microtemporal relaxation of luminescence from porous silicon under pulsed photoexcitation: namely, a relative increase in the rate of macrorelaxation for the slower components of the luminescence. Spectral investigations show that the difference in the rates of fatigue relaxation “tiredness” is maximum at the long-wavelength edge of the luminescence band. We propose a model that allows us to explain the observed effects starting from the assumption that photoexcitations drift toward radiative recombination centers. Fiz. Tverd. Tela (St. Petersburg) 39, 1165–1169 (July 1997)     

Spectral-luminescent parameters of the amniotic fluid

Absorption and luminescence excitation and emission spectra of the amniotic fluid from females with a normal course of pregnancy and with fetation anomalies are investigated. It is shown that the amniotic fluid manifests, in addition to an intense UV luminescence, a luminescence in the range of 380–650 nm. The first luminescence peak with λ_max = 430–450 nm is most likely due to the presence of NADH₂ and hormones in the amniotic fluid, whereas the peak located at longer wavelengths with λ_max = 520–540 nm is due to pigments (bilirubin, etc.). Differences in absorption spectra of the amniotic fluid in the case of the normal course of pregnancy and upon its pathologies are established. Luminescence emission and excitation spectra of the amniotic fluid in cases of intrauterine fetation pathologies are shifted toward the longwave region compared to normal pregnancy cases. It is concluded that the spectral-luminescent analysis of the amniotic fluid can be used as an additional rapid test for monitoring of intrauterine fetal pathologies. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 939–942, November–December, 1998.     

Recombination kinetics in nonlinear defective LiB3O5 crystals

A study of recombination kinetics in LiB₃O₅ (LBO) crystals by time-resolved luminescence and absorption spectroscopy is reported. An investigation of the kinetics of transient optical absorption (TOA) and luminescence under ns-scale electron-beam excitation performed within a broad temperature range of 77–500 K and a 1.2–5-eV spectral interval has established that the specific features in the recombination kinetics observed in LBO involve electronic, B²⁺, and hole, O⁻, trapping centers. The TOA and luminescence kinetics, as well as their temperature dependence, are interpreted by a model of competing hole centers. Relations connecting the kinetics parameters and the temperature dependence to the parameters of the main LBO point defects are presented. Fiz. Tverd. Tela (St. Petersburg) 40, 2008–2014 (November 1998)     

Excitation cross sections for a vanadium atom

Moscow Power Engineering Institute, 14 Krasnokazarmennaya Str., Moscow, 105835, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 6, pp. 16–21, November–December, 1995.     

The effect of oxygen on the excition spectra of A2B6 compounds

The exciton cathode luminescence and reflection spectra are studied for pure ZnSe with deviation from stoichiometry within a bilateral homogeneity region and a sharp change in the oxygen concentration from 3·10¹⁸ to 2·10²⁰ cm⁻³. It is confirmed that the exciton b and is not shifted and, consequently, that the forbidden band does not change with the oxygen concentration. This effect is interpreted on the basis of the interaction of oxygen with intrinsic point defects. It is found that dissolution, of oxygen enhances the excitonphonon interaction, which results in additional absorption within the A_ex-1LO or A_ex-2LO spectral region. It is shown that this effect is also characteristic of other compounds A₂B₆. Moscow Institute of Power Engineering, 14, Krasnokazarmennaya St., 111250, Moscow B-250, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 394–399, May–June, 1998.     

The effect of electron irradiation on the optical properties of the natural armenian zeolite-clinoptilolite

Infrared (IR) absorption and luminescence in chemically and radiation-modified natural Armenian Zeolite (clinoptilolite) samples have been studied. The luminescence was studied in 390–450 nm and 620–710 nm wavelength bands, and the IR measurements were carried out in the 400–5400 cm⁻¹ range. It is shown that the luminescence intensity depends on the content of pure clinoptilolite in the samples and, probably on the distribution of “passive” luminescence centers over Si and Al sites that became “active” under radiation or chemical treatment. The samples of electron irradiated clinoptilolite have higher luminescence intensity than the chemically and thermally treated ones. A decrease in the intensity of IR absorption bands at 3550 cm⁻¹ and 3650 cm⁻¹ was found after irradiation.     

Time-resolved spectroscopy of natural and synthetic BeO crystals

The results of comparative luminescence investigation of natural and synthetic BeO crystals are presented. Time-resolved luminescence (2.5–8 eV) and luminescence excitation spectra, and the kinetics of glow decay were measured using ultraviolet-vacuum-ultraviolet (VUV) synchrotron radiation (5–22 eV) or x-radiation (50–620 eV or 3–62 keV) ranges. X-ray and thermostimulated luminescence of natural BeO crystals were compared to the glow of additively colored synthetic crystals. The characteristic luminescence of F and F ⁺ centers was found in natural crystals. In synthetic crystals similar luminescence is observed only after additive or radiation coloration by virtue of the creation of F ⁻ and F ⁺ centers on anion vacancies. The defects found in the crystal lattice of a natural BeO crystal testify to the degree of mineral metamictization of the given deposit.     

Upconversion luminescent characteristics and peak shift of CdSeS nanocrystals under different wavelength laser excitation

Upconversion luminescence was obtained from CdSeS nanocrystals (NCs) under 800 nm femtosecond laser excitation. The structural and optical characteristics of the CdSeS NCs were investigated experimentally by use of UV–visible absorption spectroscopy, transmission electron microscopy, X-ray diffractometry, and time-resolved luminescence dynamics. Peak shift of luminescence in CdSeS NCs can be readily observed under different wavelength femtosecond excitation. The pump power dependence of the luminescence intensity and time-resolved decay revealed that one, two, and three-photon absorption occur. It was found that upconversion luminescence is composed of photoinduced trapping and a band-edge excitonic state, and two types of species are involved in the biexponential luminescence decay kinetics. With increasing Se-doped composition, luminescence lifetimes of CdSeS NCs with similar sizes become shorter. This is not consistent with the changes of undoped CdS NCs and is ascribed to impurity level increased doping in the energy gap, which is favorable for trapping luminescence. A simple energy level of doping NCs is used to interpret upconversion luminescence and the peak shift of steady-state emission.     

Degree of coherence and dimensions of the generation region of powder lasers

A degree of coherence of powder-laser radiation of 10–20% is estimated by the magnitude of the image contrast for a speckle, although cases are recorded where it attains 40–50%. It is found that as the average speckle intensity increases, the contrast decreases. It is established that the minimum, dimensions of the generation region in powders are 20–30 μm. Cases of existence of several generation centers simultaneously are noted. An attempt to interpret the results obtained is made. Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 11, Mokhovaya St., Moscow, 103907. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 780–786, September–October, 1998.     

Copper-Ion Sensitization of the Luminescence of Tb<Superscript>3+</Superscript> in a Solution of a Binuclear Complex

It has been established that copper ions can effectively sensitize the luminescence of lanthanides in a solution of the different-metal Tb-Cu complex with podand that contains hydrazine fragments and ether atoms of oxygen with which Cu and Tb are coordinated, respectively. The maximum sensitization is observed in a solution of the Tb-Cu complex at pH 6.2, which is also optimal for formation of a monometallic complex of copper. There is no sensitization in a solid complex. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 582–585, September–October, 2005     

Excitation cross-sections of erbium-atom resonance lines

Moscow Power Institute, 14, Krasnokazarmennaya Str., E-250, Moscow, 105835. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 63, No. 6, pp. 883–888, November–December, 1996.     

Electronic excitations of Sc3+ impurity in α-Al2O3 crystals

Optical properties, including luminescence, of scandium-doped α-Al₂O₃ crystals have been studied in the VUV range. An absorption band associated with the scandium impurity was observed at the fundamental-absorption edge of crystalline corundum. A strong luminescence band peaking at 5.6 eV, which is most effectively excited within the 7.7–8.8-eV interval, was found. The kinetic and polarization characteristics of this luminescence were studied within the temperature range 6–500 K. An excitation model of the impurity complex and the mechanism of its relaxation are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 653–654 (April 1998)     

Luminescent properties of crystalline lithium triborate LiB3O5

A study of the luminescence characteristics of crystalline lithium triborate LiB₃O₅ (LBO) is reported. Investigation of the excitation and photoluminescence spectra of nominally pure, oriented LBO crystals within broad spectral (1.2–10.5 eV) and temperature (8–500 K) regions, complemented by optical spectroscopy at the long-wavelength fundamental-absorption edge, has revealed that the broad-band LBO luminescence in the 3.5–4.5-eV region is efficiently excited by photons having energies above 7.5 eV in recombination processes and under corpuscular or x-ray irradiation. The totality of the experimental data obtained permitted a conclusion that the LBO luminescence has an intrinsic nature and that it originates from radiative decay of relaxed electronic excitations. Fiz. Tverd. Tela (St. Petersburg) 41, 223–228 (February 1999)     

Photoluminescence of calcite crystals of different origins

We have studied the photoluminescence of calcite crystals. In the blue region of the photoluminescence spectrum of calcite crystals obtained from Siberia (Russia) and from Saaremaa Island (Estonia), three strongly overlapping luminescence bands due to intrinsic defects are observed. Luminescence due to impurities in the crystals are hardly detectable. The experimentally measured time dependence of the luminescence intensity for the indicated luminescence bands is compared with the dependences obtained as a result of a calculation based on a proposed model for the luminescence center. Better agreement between experiment and calculation is achieved if the model of the luminescence center includes a metastable level with electron ejection energy of 4 meV; the characteristic time for the radiative transition is 1.3 nsec. Studying the time dependence of the luminescence at different wavelengths within the indicated bands allows us to conclude that the photoluminescence (three bands) is due to one type of luminescence center. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 498–501, July–August, 2006.