Luminescence of CsBr:Eu films grown by liquid-phase epitaxy

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu²⁺ ions (λ = 337 nm) includes Eu²⁺-V_Cs isolated dipole centers and CsEuBr₃ aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH⁻ with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH⁻ ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 191–194, March–April, 2006.     

Spectroscopic investigation of the plasma of a high-current diffuse discharge in He/Ar/CF2Cl2(CCl4) mixtures

Survey emission spectra in the region of 190–600 nm and time and service-life characteristics of a transverse nanosecond discharge in He/Ar/CF₂Cl₂(CCl₄) mixtures at a pressure of 10–100 kPa are investigated. In the emission spectra, excited products of the decomposition of freons—C₂(A−X), CN(B−X), Cl ₂ ^* , C^*, Cl^*, and Cl^+*— and the emission of ArF at λ=193 nm are revealed. The emissions of Cl ₂ ^* at λ=258 nm and ArF at λ=193 nm were the most intense. The discharge in the He/Ar/CF₂Cl₂ mixture is a multiwave emission source with λ=258 nm Cl ₂ ^* 193 nm ArF, and probably, 175 nm Arcl. It is of interest for applications in UV-VUV-range pulse photometry. The duration of the emission on Cl ₂ ^* , ArF, ArI, ClI, and ClII transitions in the discharge in the Ar/CF₂Cl₂ mixture (P=10–20 kPa) was 200–300 nsec. With adding He and increasing pressure to 100 kPa the duration of the emission decreased by a factor of 1.5–2. The basic mechanisms of the formation of Cl₂, ArF, and CN(B) molecules in the transverse-discharge plasma are considered. Uzhgorod State University, 46, Pidgirna Str., Uzhgorod, 294000, Ukraine. Translated from Zhurnal. Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 241–246, March–April, 1999.     

Photoconversion of 2-methylphenol, 4-methylphenol, and 2-amino-4-methylphenol in water

We have used fluorescence spectroscopy to study photoconversions of 2-methylphenol (2-MP), 4-methylphenol (4-MP), and 2-amino-4-methylphenol (2-A-4-MP) in water when excited by UV radiation from different sources. We discuss the effect of the acidity of the medium and dissolved oxygen on photoconversions of the indicated methylphenols. The photodegradation efficiency for 2-MP and 4-MP decreases in the absence of oxygen. The photoconversion efficiency for methylphenols in alkaline medium is higher when irradiated by light with λ_rad = 283 nm, while in neutral medium it is higher when irradiated by light with λ_rad = 222 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 566–572, September–October, 2006.     

Spectral and kinetic properties of fluorescence of immunoactive steroids in the gas phase

We have used steady-state fluorescence spectroscopy and pulsed kinetic fluorimetry with high time resolution to experimentally study the spectral and temporal characteristics of luminescence of immunoactive 8-aza-D-homogona-1,3,5(10), 13-tetraene-12,17a-dione (8-aza-D-homogonane) molecules in the gas phase. We have established the existence of several centers emitting long-wavelength and short-wavelength fluorescence. The fluorescence of high-temperature 8-aza-D-homogonane vapor (T = 550 K) when excited by radiation with λ_ex = 266 nm is represented by two spectrally separated emission bands with maxima λ _max ^fl = 465 nm and λ _max ^fl = 365 nm. Analysis of the distribution of fluorescence decay times for 8-aza-D-homogonane showed that in the spectral range of the emission wavelengths 360–590 nm, the fluorescence decay kinetics contains three components with average lifetimes <200 psec, 2.8 nsec and 13.5 nsec. The multicenter nature of luminescence of 8-aza-D-homogonane was confirmed by direct measurements of instantaneous fluorescence spectra in different stages of luminescence decay. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 309–314, May–June, 2006.     

Structure and optical properties of carbon films obtained by multipulse pulsed laser deposition

We have obtained carbon thin films on silicon and glass substrates with multipulse pulsed laser irradiation of graphite under vacuum (p ≈ 2.6 Pa) using a high-frequency series of nanosecond laser pulses (τ = 85 ns, λ = 1060 nm) with pulse repetition frequency f ≈ 10–20 kHz and laser power density q ≈ 15–40 MW/cm². We established the optimal laser power density and laser pulse repetition frequency for obtaining amorphous nanostructured diamond-like films.     

Ion-implanted buried layer in diamond as a source of ballistic phonons at liquid-helium temperatures

It is shown that an approximately 150 nm thick ion-implanted buried layer in diamond and excited by a pulsed laser at wavelength λ=337 nm is a source of nonequilibrium acoustic phonons propagating ballistically through the diamond sample at temperatures ∼2 K. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 270–272 (25 August 1996)     

Corrugated neat thin-film conjugated polymer distributed-feedback lasers

Wave-guided thin-film distributed-feedback (DFB) polymer lasers are fabricated by spin coating a PPV-derived semiconducting polymer, thianthrene-DOO-PPV, onto oxidised silicon wafers with corrugated second-order periodic gratings. The gratings are written by reactive ion beam etching. Laser action is achieved by transverse pumping with picosecond laser pulses (wavelength 347.15 nm, duration 35 ps). The DFB-laser surface emission and edge emission are analysed. Outside the grating region the polymer film is used for comparative wave-guided travelling wave laser (amplified spontaneous emission (ASE)) studies. The pump pulse threshold energy density for wave-guided DFB-laser action (4–9 μJ cm^-2) is found to be approximately a factor of two lower than the threshold for wave-guided travelling wave laser action. The spectral width of the DFB laser (down to Δλ_DFB≈0.07 nm) is considerably narrower than that of the travelling wave laser (Δλ_TWL≈14 nm). The DFB-laser emission is highly linearly polarised transverse to the grating axis (TE mode). Only at high pump pulse energy densities does an additional weak TM mode build up. The surface-emitted DFB-laser radiation has a low divergence along the grating direction. For both the DFB lasers and the travelling wave lasers, gain saturation occurs at high excitation energy densities. Received: 7 January 2002 / Revised version: 15 February 2002 / Published online: 14 March 2002     

Effect of polarization and coherence of low-intensity optical radiation on fish embryos

  We have shown that brief exposure of sturgeon embryos (fertilized roe) in the organogenesis stage to low-intensity radiation in the visible region of the spectrum can have a long-term effect on embryonic and post-embryonic development of the fish, detectable 50 days after the irradiation procedure. The biological effects (size-weight characteristics and hardiness parameters of the fish relative to unfavorable habitat conditions) induced by linearly polarized emission from a monochromatic laser source (helium-neon laser, λ = 632.8 nm, Δλ ≈ 0.02 nm) and a quasi-monochromatic light-emitting diode (LED) source (maximum in emission spectrum λ = 631 nm, Δ λ = 15 nm) are practically the same. Going to broadband linearly polarized radiation (λ = 420–800 nm) is accompanied by a decrease in the biological effect. From the results of studies of the effect on embryos from linearly polarized and unpolarized radiation from an LED source and also the effect of linearly polarized, circularly polarized, and unpolarized radiation from a helium-neon laser, we concluded that the type of polarization is of critical importance in realization of the biological effect of radiation. In this case, the maximum stimulating effect (on the size×weight characteristics and the hardiness parameters for juvenile fish) is observed on exposure to linearly polarized radiation; the photobiological effect induced in the same dose range by light with natural polarization (i.e., unpolarized) is significantly less pronounced; the stimulating effect of circularly polarized radiation occupies an intermediate position. Based on the presented data and also on data obtained previously, we conclude that among the resonant and nonresonant photophysical processes (orientational effect of light, effect of gradient forces, dipole-dipole interactions, thermooptic processes) capable of inducing photobiological effects dependent on such laser-specific characteristics as polarization and coherence, the determining influence in the processes studied in this work comes from the orientational effect of light and dipole×dipole interactions. And the orientational effect can appear for anisotropic media with liquid-crystal type ordering (especially domains in membranes and multiple-enzyme complexes) both under conditions when there is no resonant absorption and for weakly absorbing structures, and can initiate a change in their conformations and accordingly their functional characteristics. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 843–858, November–December, 2008.     

Laser mass spectrometry study of the properties of fullerene structures

Fullerene films grown by various methods are studied using mass spectrometry. The mass spectra of the films formed onto an aluminum foil using thermal deposition (TD) or supersonic molecular beam (SMB) exhibit a small change in the mass peak distribution in the C₁₂₀ dimer range as compared to the initial fullerene powder during desorption by laser radiation irrespective of the radiation wavelength (λ = 259, 518 nm). Under the action of laser radiation with wavelength λ = 259 nm, fullerene films grown on a silicon substrate with an SMB also exhibit a small change in the mass peak distribution in the C₁₂₀ dimer range. At λ = 518 nm, the mass peak distribution in the dimer range shifts significantly toward small masses, so that the intensity maximum corresponds to M ≅ C₁₀₂. This fact is assumed to be related to the polymerization of an SMB fullerene film caused by heating due to the absorption of laser radiation with a wavelength λ = 518 nm.     

Effect of <Emphasis Type="Italic">in vivo</Emphasis> irradiation of blood by low-intensity emission from a He–Ne laser on molecular components of blood

We have used the IR absorption spectra of blood, plasma, and packed erythrocytes to study the effect of in vivo exposure of blood to low-intensity emission from a He–Ne laser (λ = 632.8 nm, 4 mW/cm²) on the molecular components of blood. In comparing the IR spectra of samples of blood sample and blood components before and after irradiation, we identified changes in the amide A, amide I, amide II, amide III absorption regions and also in the absorption bands of methyl, methylene, and phosphate groups. We conclude that exposure of blood in vivo to emission from a He–Ne laser leads to a decrease in the contribution of the α-helix conformation in the secondary structure of the blood proteins.     

Simultaneous operation at two different wavelengths of an PrLaP5O14 laser

Simultaneous laser operation at the wavelengths of λ₁=637 and λ₂=717 in Pr_0.5La_0.5P₅O₁₄ single crystals was observed. The crystals were excited by nanosecond publses from a Coumarin 2 dye laser (λ=450 nm). Laser emissions and their interdependence were studied both in crystals without an external resonator and in crystals placed within a plane parallel resonator. The energetic, time and frequency characteristics for both laser actions were examined. The effect of bifrequential emission was also found in crystals of different ratios of Pr and La ions concentration and in pure praseodymium pentaphosphate.     

Photoluminescence of nanostructured cubic-lattice silicon carbide films grown on a silicon wafer

The light-emitting properties of cubic-lattice silicon carbide SiC films grown on Si(100) and Si(111) substrates with VPE at low temperatures (T _gr ∼ 700°C) are discussed. Investigations of the grown films reveal a homogeneous nanocrystalline structure involving only the 3C-SiC phase. When the electron subsystem of the structure is excited by a He-Cd laser emitting at λ_exit = 325 nm, the photoluminescence (PL) spectra contain a rather strong emission band shifted by about 3 eV toward a short-wave spectral region. At low temperatures, the PL integral curve is split into a set of Lorentz components. The relation between these components and the peculiarities of the energy spectrum of electrons in the nanocrystalline grains of the silicon carbide layers is discussed.     

Determination of the optical bandgap for diamond-like carbon films obtained by laser plasma deposition

We have obtained and analyzed the optical transmission spectra of diamond-like carbon films deposited on quartz substrates by pulsed laser deposition (λ = 1064 nm, τ = 20 nsec, q = 4.9·10⁸ W/cm²) under vacuum (p = 2.6·10⁻³ Pa). Based on the spectra obtained, we have estimated the size of the bandgap by the Tauc method, and also have studied the growth dynamics of the coatings formed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 637–641, September–October, 2007.     

Critical role of laser wavelength on carbon films grown by PLD of graphite

The structure of thin films deposited by pulsed laser ablation (PLD) is strongly dependent on experimental conditions, like laser wavelength and fluence, substrate temperature and pressure. Depending on these parameters we obtained various kinds of carbon materials varying from dense, mainly tetrahedral amorphous carbon (ta-C), to less compact vertically oriented graphene nano-particles. Thin carbon films were grown by PLD on n-Si 〈100〉 substrates, at temperatures ranging from RT to 800°C, from a rotating graphite target operating in vacuum. The laser ablation of the graphite target was performed by a UV pulsed ArF excimer laser (λ=193 nm) and a pulsed Nd:YAG laser, operating in the near IR (λ=1064 nm). The film structure and texturing, characterised by X-ray diffraction analysis, performed at grazing incidence (GI-XRD), and the film density, evaluated by X-ray reflectivity measurements, are strongly affected both by laser wavelength and fluence and by substrate temperature. Micro-Raman and GI-XRD analysis established the progressive formation of aromatic clusters and cluster condensation into vertically oriented nano-sized graphene structures as a direct function of increasing laser wavelength and deposition temperature. The film density, negatively affected by substrate temperature and laser wavelength and fluence, in turn, results in a porous bulk configuration and a high macroscopic surface roughness as shown by SEM characterisation. These structural property modifications induce a relevant variation also on the emission properties of carbon nano-structures, as evidenced by field emission measurements. This work is dedicated to our friend Giorgio who passed away 20th August.     

Pulsed lasers operating by the atomic transitions of inert gases on pumping by a self-sustained transverse discharge

This paper presents the results of experimental studies of lasing by the atomic transitions of inert gases in mixtures ofHe−NF ₃ (λ=706.5 nm),Ne−NF ₃ (585.3 nm), andAr−NF ₃ (750.4 nm). It has been shown that when an inert-gas-halide mixture is excited by a self-sustained discharge, the electronegative gas provides depopulation of the lower laser level and simultaneously increases the pumping efficiency. Based on investigations of the spontaneous emission and lasing, on measurements of the density and temperature of the gas-discharge plasma electrons, and on an analysis of the process rates, it is concluded that the processes of electron excitation play a dominant role in the population of the upper laser level. Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 60–63, April, 2000.     

Synchrotron and laser excitation of luminescence in PbWO<Subscript>4</Subscript>:Tb crystals at different temperatures

The effect of temperature on the spectral luminescence characteristics of PbWO₄:Tb³⁺ crystals with synchrotron and laser excitation is studied. If PbWO₄:Tb³⁺ is excited by synchrotron radiation with λ = 88 nm at 300 K, a faint recombination luminescence of the impurity terbium is observed against the matrix luminescence. When the temperature is reduced to 8 K, the luminescence intensity of PbWO₄:Tb³⁺ increases by roughly an order of magnitude and the characteristic luminescence of the unactivated crystal is observed. Excitation of PbWO₄:Tb³⁺ by a nitrogen laser at 300 K leads to the appearance of emission from Tb³⁺ ions. At 90 K, a faint matrix luminescence is observed in addition to the activator emission. The formation of the luminescence excitation spectra for wavelengths of 60–320 nm is analyzed and the nature of the emission bands is discussed.     

Upconversion emission in Er<Superscript>3+</Superscript>-doped lead niobium germanate thin-film glasses produced by pulsed laser deposition

Thin films of Er³⁺-doped lead–niobium germanate have been produced by pulsed laser deposition from Er³⁺-doped 25PbO₂–25Nb₂O₅–50GeO₂ (mol%) transparent glasses with an Er content in the range 0.5–3 wt%. The room-temperature infrared to visible upconversion properties of these thin films have been investigated under 800-nm laser excitation. An energy transfer upconversion mechanism has been identified to be responsible for the population of the ⁴S_3/2:²H_11/2 excited level, from which an intense green emission occurs. A rate equation analysis supports the proposed mechanism.     

Fluorescence and absorption of polystyrene exposed to UV laser radiation

We show that when polystyrene is exposed (for 15–60 sec) to a UV laser light beam (λ = 248 nm), its absorption and luminescent properties change significantly. In the irradiated polymer, optical centers are formed with absorption bands in the 280–460 nm region and fluorescence bands in the 330–520 nm region. We have established the chemical structure of the optical centers for fluorescence of polystyrene. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 1, pp. 54–58, January–February, 2006.     

Naturally grown Ag nanoparticles on quartz substrates as SERS substrate excited by a 488 nm diode laser system for SERDS

A silver nanoparticle ensemble was prepared under ultrahigh vacuum (UHV) conditions by Volmer–Weber growth on a quartz substrate for surface-enhanced Raman scattering (SERS) investigations of pyrene molecules. To tune the surface plasmon resonance frequency in the vicinity of the excitation wavelength of 488 nm of the diode laser, the morphology of the silver nanoparticles was optimized. The substrates were mounted in a flow-through cell as part of the optical Raman set-up. A microsystem diode laser generates two slightly different emission wavelengths (λ=487.61 nm and λ=487.91 nm) with a spectral width <10 pm and an optical power of 20 mW, i.e. SERS experiments are possible but also shifted excitation Raman difference spectroscopy (SERDS) can be carried out. For trace analysis of pyrene in water we demonstrate SERS/SERDS experiments which lead to a limit of detection of 2 nmol/l for pyrene. These results suggest that with silver nanoparticle ensembles excited at their plasmon resonance at 488 nm combined SERS/SERDS measurements can be effectively performed for in-situ trace analysis of pollutant chemicals in water.