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.     

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.     

Regularities of the photoluminescence of porous silicon after chemical etching in HF

The effect of chemical treatment of porous silicon samples by HF on its photoluminescence and its evolution with time in sample aging in air is investigated. It is shown that the effect of HF on the luminescence parameters depends on the duration of the treatment and the initial photoluminescence intensity of the sample. It is found that chemical etching in HF accelerates the growth of the total luminescence intensity in aging of the sample in air. The evolution of the photoluminescence spectrum in aging of the sample in air after chemical etching can be explained within the framework of the quantum-size model of the luminescence of porous silicon. Presented at the Fall Meeting of the Material Research Society, December 1–5, 1997, Boston, USA Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 423–427, May–June, 1999.     

Anti-stokes luminescence of solid AgCl<Subscript>0.95</Subscript>I<Subscript>0.05</Subscript> solutions

An anti-Stokes luminescence band with λ_max = 515 nm of microcrystals of solid AgCl_0.95I_0.05 solutions excited by a radiation flux of density 10¹³–10¹⁵ quanta/cm²·sec in the range 600–800 nm at 77 K was detected. It is shown that the intensity of this luminescence and the frequency of its excitation depend on the prior UV-irradiation of samples. Analysis of the stimulated-photoluminescence spectra and the anti-Stokes luminescence excitation spectra of the indicated microcrystals has shown that to the centers of anti-Stokes luminescence excitation correspond local levels in the forbidden band of the crystals. These states are apparently due to the atomic and molecular disperse silver particles that can be inherent in character or formed as a result of a low-temperature photochemical process. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 738–742, November–December, 2005.     

Effect of finely dispersed platinum on the structure of luminescence spectra of the adsorbates of magnesium phthalocyanine on silicon dioxide

The luminescence and excitation spectra and kinetic characteristics of the luminescence of the adsorbates of magnesium phthalocyanine (MgPhc) on SiO₂ and the effect on them of surface hydration and finely dispersed platinum are studied. It is found that a structure that improves hydration of the adsorbent surface appears on the platinized surface in the luminescence and excitation spectra. It is assumed that the spectral structure is due to the complexes of MgPhc formed with water molecules, the hydroxyl cover of the surface, and the surface centers of SiO₂ modified by a Pt-catalyst. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 552–555, July–August, 1999.     

Photo- and Thermobleaching of Luminescence Centers in Synthetic Opals

It has been found that on exposure of specimens of synthetic opal to UV radiation, luminescence is excited in them (337 nm) that has spectral maxima at 400 and 500 nm. Its duration at half-height of a pulse is 9 nsec, and there is a weak slow component with τ ∼ 1 μsec. The spectrum and intensity of the luminescence depend on the duration of irradiation and temperature. The luminescence bands revealed relate to two individual luminescence centers, namely: the shortwave one, caused by the luminescence centers formed in the bulk of the opal, and the longwave one, due to those formed on the opal surface. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 622–626, September–October, 2005.     

Luminescence Properties of Metal(II)-Diethyldithiocarbamate Chelate Complex Particles and Its Analytical Application

In a suitable pH buffer solutions, sodium diethyldithiocarbamate (DDTC) reacts with some divalence metal ions M(II) to form (M–DDTC) _n chelate complex nanoparticles, which exhibit different luminescence properties. There is a strongest luminescence peak at 470 nm for the Co(II)–DDTC system, three peaks at 330, 470, and 630 nm for the Cu(II)–DDTC system, three peaks at 420, 470, and 630 nm for the Cd(II)–DDTC system, four peaks at 350, 400, 435, and 470 nm for the Ni(II)–DDTC system, two peaks at 408 and 470 nm for the Pb(II)–DDTC system, two peaks at 415 and 470 nm for the Fe(II)–DDTC system. The different luminescence properties of (M–DDTC) _n chelate complex nanoparticles was explained. Under the optimal conditions, the luminescence intensity of (Co–DDTC) _n chelate complex nanoparticles at 470 nm (F _{470 nm}) is linear to Co(II) concentration in the range of 0.012–1.44 μg/mL. The detection limit is 0.0023 μg/mL. A novel luminescence method has been proposed for the determination of cobalt in Vitamin B₁₂ samples, with satisfactory results.     

Fluorescence and absorption of a polystyrene-based scintillator exposed to UV laser radiation

We have established that exposure of polystyrene-based scintillator samples to UV laser radiation (248 nm) leads to a significant decrease in the fluorescence intensity. We have carried out a spectral analysis of the luminescent and absorption properties of the scintillator, which allowed us to determine the major factor in the decrease in luminescence intensity of the samples exposed to UV radiation. We propose a new hypothesis for the mechanism of the processes leading to the decrease in light output of the scintillator during operation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 744–749, November–December, 2007.     

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.     

Luminescence of thulium-activated cubic boron nitride

Under high pressure and temperature conditions, we have obtained samples of thulium-activated cubic boron nitride in the form of micropowders, ceramics, and polycrystals activated by thulium in the presence of aluminum. We studied the cathodoluminescence (CL), photoluminescence (PL), and photoluminescence excitation spectra of the samples. In the luminescence spectra we observe structured bands with maxima at ∼370, ∼475, ∼660, and ∼ 800 nm, assigned to electronic transitions in the triply charged thulium ions. We have established that the most efficient method for excitation of “blue” luminescence at ∼475 nm for thulium ions in cBN is excitation by an electron beam. The cBN samples synthesized in the presence of Al have photoluminescence spectra with a more complex structure compared with samples not containing Al, with the band of dominant intensity at about 660 nm. Hypothetically, this is a consequence of incorporation of thulium ions into the crystalline phases cBN and AlN, which are equally likely to be formed during synthesis. The observed photoluminescence spectrum of the indicated samples is the superposition of the photoluminescence spectra of the Tm³⁺ ions located in the crystal fields of cBN and AlN of different symmetries. The presence in the photoluminescence excitation spectra (at 450, 490, and 660 nm) of structure, with features at wavelengths shorter than the excited photoluminescence, suggests a nonresonant mechanism for its excitation. We have established that luminescence of Tm³⁺ ions is less intense than for other rare earth elements incorporated into cubic boron nitride. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 4, pp. 547–555, July–August, 2008.     

Acid Synthesis of Luminescent Amine-functionalized or Erbium-doped Silica Spheres for Biological Applications

In this work we discuss and investigate the morphological and optical properties of luminescent silica spheres which can have interesting applications in bioimaging and biosensing. The spheres are synthesized following an acid route by the hydrolysis and condensation of tetraethylortosilicate (TEOS) and can be functionalized by incorporation of aminopropyl-triethoxysilane (APTES) during the synthesis, inducing a significant luminescence that can be attributed to a recombination mechanism from localized organic defects related to –NH₂ groups. It is shown that the acid synthesis route produces very regular spherical particles, but their diameter vary in the range of 200–4,000 nm. The luminescence properties have been investigated and optimized by variation of the annealing temperature for the functionalized spheres, obtaining the most efficient PL emission after a thermal treatment of 1 h at 600 °C in air. Moreover, the possibility to introduce rare earths like erbium in the spheres was also studied and the corresponding Er³ luminescence emission at 1.53 μm is reported in terms of intensity and lifetime, pointing out that erbium can be easily and efficiently incorporated during the acid synthesis giving high PL intensity with a good lifetime of 3.9 ms.     

Effect of alkali-metal doping on photoluminescence of CdS films

It is established that doping of CdS polycrystalline films with alkaline metals (Li, Na, K, Cs) results in an increase of luminescence intensity by 3–5 times compared with pure films. This increase is accounted for by the placement of alkaline-metal ions in V _Cd ²⁻ cation vacancies, which are nonradiative recombination centers in these films. From the dependences of the luminsecence intensity of the doped films on the synthesis conditions (deposition temperature, concentration of doping impurities, type of doping metal), the parameters that ensure the maximum luminescence intensity of the films are determined as T_dep ≈ 450°C and C_Me = 1·10⁻⁵ at %. The luminescence intensity decreases by 1–3% upon exposure of the films to UV light (λ_max = 365 nm, I = 10²¹ quanta·sec·cm⁻¹) for several hours. This is indicative of the stability of these films against UV radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 362–366, May–June, 2007.     

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.     

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.     

Effect of surface groups on the luminescence property of ZnO nanoparticles synthesized by sol–gel route

Structural and optical properties of ZnO nanoparticles of diameter ~ 5 nm synthesized by a sol–gel route, have been studied using a variety of experimental techniques. The photoluminescence (PL) study carried out on these particles in the atmospheric and vacuum conditions shows a suppression of the defect related green luminescence (GL) band and a simultaneous enhancement of the near-band-edge ultra violet luminescence (UVL) when the surroundings of the nanoparticles are evacuated. This observation clearly suggests that GL is originating from certain groups that are physisorbed on the surface of the nanoparticles. Fourier transform infrared spectroscopy (FTIR) that has also been conducted at the vacuum and atmospheric conditions reveals the presence of the hydroxyl and the acetate groups in these nanoparticle samples. These groups are also found to be removed upon evacuation, suggesting that there is physical adsorption on the surface of the nanoparticles. When the PL spectrum is recorded again at the atmospheric condition, the GL intensity recovers almost up to its original value. Since there are substantial amount of water molecules present in air, which can source the hydroxyl groups, while the acetate groups are not expected to be abundant in air, this finding further suggests that the hydroxyl groups rather than the acetate groups are the likely cause for the GL emission observed in this system.     

Experimental Investigation and Modeling of the Cathodoluminescence of 1,2,4-Triazine Derivatives

We carried out experimental and theoretical investigations of the luminescence characteristics of 1,2,4-triazine derivatives and revealed the factors of a molecular structure that determine the cathodoluminescence wavelength. We obtained a satisfactory agreement between the experimental and calculated spectral characteristics. A number of reasons for the bathochromic and hypsochromic shifts of bands and also a change in the intensity of the pulsed cathodoluminescence were determined. Luminophor fragments of compounds have been revealed. We suggested variants of structural changes to increase the intensity and shift of the luminescence bands. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 586–590, September–October, 2005.     

Luminescence and thermally stimulated recombination processes in Li<Subscript>6</Subscript>Gd(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Ce<Superscript>3+</Superscript> crystals

The luminescence and thermally stimulated recombination processes in lithium borate crystals Li₆Gd(BO₃)₃ and Li₆Gd(BO₃)₃:Ce have been studied. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence), temperature dependences of the intensity of steady-state X-ray luminescence (XL), and thermally stimulated luminescence (TSL) spectra of these compounds have been investigated in the temperature range of 90–500 K. The intrinsic-luminescence 312-nm band, which is due to the ⁶ P _J → ⁸ S _7/2 transitions in Gd³⁺ matrix ions, dominates in the X-ray luminescence spectra of these crystals; in addition, there is a wide complex band at 400–420 nm, which is due to the d → f transitions in Ce³⁺ impurity ions. It is found that the steady-state XL intensity in these bands increases several times upon heating from 100 to 400 K. The possible mechanisms of the observed temperature dependence of the steady-state XL intensity and their correlation with the features of electronic-excitation energy transfer in these crystals are discussed. The main complex TSL peak at 110–160 K and a number of minor peaks, whose composition and structure depend on the crystal type, have been found in all crystals studied. The nature of the shallow traps that are responsible for TSL at temperatures below room temperature and their relation with defects in the lithium cation sublattice are discussed.     

Thermally stimulated luminescence of yttrium oxide in a transparent dielectric medium

The thermally stimulated luminescence of Y₂O₃ in contact with a dielectric is investigated. The measurements were carried out in an atmosphere of dry air, in glycerol, ethylene glycol, and water. Shifting of the spectrum of thermally stimulated luminescence and decrease in the luminescence intensity with an increase in the dielectric constant of the medium were revealed. A discussion of the results is presented. I. I. Mechnikov Odessa State University, 2, Dvoryanskaya St., Odessa, 270026, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 462–463, May–June, 1998.     

Luminescence quenching of lanthanides in complexes with β-diketones containing different fluorinated radicals

It is shown that luminescence quenching of lanthanide (Ln) ions by water molecules (OH-oscillators) entering the first coordination sphere of a complex decreases as the chain of the fluorinated radical lengthens from CF₃ to C₆F₁₃. The amounts of water molecules in binary and different-ligand Eu complexes with some fluoro derivatives of acetyl acetone are determined. It is established that, unlike OH-oscillators, the elimination of hydrogen oscillations at the central carbon atom by β-diketone deuteration provides the same increase (1.1–1.2 fold) in luminescence intensity in all the investigated Eu complex compounds. A. V. Bogatskii Physicotechnical Institute, National Academy of Sciences of Ukraine, 86, Lyustdorfskaya Read, Odessa, 270080, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 217–220, March–April, 1997.     

Rapid luminescence saturation of the Mn2+ 3d shell in the Cd1−x MnxTe dilute magnetic semiconductor with a high manganese concentration

The dependence of manganese-ion intracenter-luminescence intensity on optical excitation level has been studied in the Cd_1−x Mn_xTe dilute magnetic semiconductor with 0.4<x<0.7. It is shown that the intracenter luminescence saturates due to effective nonlinear quenching already at low excitation levels. Mechanisms are proposed which can provide nonlinear quenching and offer a qualitative explanation for the temperature dependence of the luminescence saturation in samples with different manganese concentrations. Fiz. Tverd. Tela (St. Petersburg) 41, 49–53 (January 1999)