Luminescence of mercurylike impurities in single-crystal CdWO4 compounds

The processes of crystallization by the method of liquid epitaxy are studied for the first time for single-crystal films of CdWO₄ doped with the mercurylike ions Bi³⁺ and Pb²⁺, which can be used as thin-film components of combined scintillators for monitoring α- and β-activities. It is shown that in comparison with their solidcrystal analogs, the special features of these films consist in a longwave shift of the integral luminescence spectrum that is caused by high concentrations of the radiating complexes (V_Cd-WO₆) with hv_max=2.05–2.15 eV and the “distorted” complexes (WO₆)^* in them. It is found that in the case of luminescence of single-crystal films CdWO₄:Pb, radiation of mercurylike centers (PbO₆) prevails with hv_max=2.87 eV, while in luminescence of CdWO4, radiation of centers (BiO₆) with hv_max=2.16 eV and of complexes (V_Cd-WO₆). Institute of Applied Physics, Iv. Franko Lvov State University, 49, General Chuprynka St., Lvov, 290044, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 211–215, March–April, 1998.     

Spectroscopic characteristics of anionic centers in α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> crystals bombarded by Cu<Superscript>+</Superscript> and Ti<Superscript>+</Superscript> ions

We have studied the effect of bombardment by Cu⁺ and Ti⁺ ions with energy 30 keV on the optical absorption and luminescence of F centers in oxygen-deficient aluminum oxide. We have shown that in the induced optical absorption spectra there are six components of gaussian shape, which can be assigned to absorption bands of F⁺, F², and F₂⁺ centers. We have established that bombardment of the samples by ion beams has a weak effect on the thermoluminescence parameters in the 3.0 eV and 2.4 eV bands, while in the 3.8 eV luminescence band for F⁺ centers, the thermoluminescent response increases considerably. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 422–424, May–June, 2008.     

Spectral and kinetic characteristics of CdI<Subscript>2</Subscript> and CdI<Subscript>2</Subscript>:Pb scintillators

We have studied the effect of lead dopant on the optical absorption, photoluminescence, and x-ray luminescence spectra, and the scintillation characteristics of CdI₂ at room temperature. The crystals for the study were grown by the Stockbarger-Bridgman method. Activation of CdI₂ from the melt by the compound PbI₂ leads to the appearance in the absorption spectra in the near-edge region of an activator band at 395–405 nm, which is interpreted as an A band connected with electronic transitions from the ¹S₀ state to the ³P₁ levels in the Pb²⁺ ion. For x-ray excitation, CdI₂:Pb²⁺ crystals with optimal dopant concentration (∼1.0 mol%) are characterized by a light yield with maximum in the 570–580 nm region that is an order of magnitude higher than for CdI₂ crystals in the 490–500 nm band. For α excitation, the radioluminescence kinetics for cadmium iodide is characterized by a very short (∼0.3 nsec) rise time and fast decay of luminescence, with τ₁ ≈ 4 nsec and τ₂ = 10–76 nsec. Depending on the conditions under which the crystals were obtained, the fast component fraction is 95%–99%. The crystal is characterized by a similar scintillation pulse in the case of excitation by x-ray pulses. The radioluminescence pulse shape for CdI₂:Pb in the decay stage is predominantly exponential, with luminescence decay time constants τ₁ ≈ 10 nsec and τ₂ = 200–250 nsec. This system is characterized by low afterglow, at the level for the Bi₄G₃O₁₂ scintillator. We have demonstrated the feasibility of using CdI₂:Pb as a scintillator for detecting α particles. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 825–830, November–December, 2008.     

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)     

Absorption and emission properties of Bi-doped Mg–Al–Si oxide glass system

A new Bi-doped Mg–Al–silicate glass is suggested and investigated. It can be fabricated by moderate-temperature routine technology. The characteristic relaxation time of 300–800 μs in combination with the high quantum yield (up to 85%) and wide excitation spectrum makes this glass a promising laser material. The obtained quadratic dependence of the visible absorption intensity is an argument in favor of the hypothesis that the absorption and infrared luminescence in Bi-doped glasses are caused by Bi₂ dimers.     

Recombination processes in europium-doped cadmium iodide crystals

Results of comprehensive research into optical and luminescent-kinetic characteristics of europium-doped cadmium iodide crystals excited by nitrogen laser radiation, α-particles, and x-rays are presented. Crystals under study have been grown by the Bridgman–Stockbarger method. The doping EuCl₃ admixture was introduced into the charge in quantities of about 0.05 and 1.0 mol%. Impurity absorption detected in the near-edge region of the crystals is interpreted as part of the Eu²⁺ ion long-wavelength band associated with f–d-transitions. The cation impurity and matrix defects in CdI₂:Eu²⁺ crystals create complex centers responsible for emission with a maximum in the 580–600-nm region. The short component in the luminescence decay kinetics of weakly-doped crystal excited by α-particles and x-ray photons is due to the exciton emission characteristic of CdI₂. The slow component in the scintillation pulse results from recombination of charge carriers followed by creation of exciton-like states on the defect-impurity centers. Laser or x-ray excitation induces light-sum accumulation on the trapping levels at a depth of 0.2–0.6 eV that is mainly related to matrix microdefects. Trapping centers associated with the chlorine impurity are observed in the heavily-doped crystal. Photostimulated luminescence at 85 K arising at the electron stage of the recombination process is caused by recombination of electrons released from F-type centers with holes localized near the activator. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 358–364, May–June, 2009.     

The absorption spectrum of radiation-colored SrCl2-Ce crystals

We investigate the spectra of the x-ray radiation-induced absorption of SrCl₂−Ce crystals over the spectral range 345–830 nm and their temperature transformations in the interval from 77 to 450 K. We found that radiative color centers are characterized by a complex spectrum of induced absorption that contains wide bands of photochromic PC (750, 519, 378 nm) and PC⁺ (620, 446, 340 nm) centers and quasi-linear bands of Ce²⁺ centers. The most significant thermal transformations of radiative color centers occur in the vicinity of the thermostimulated luminescence peak of 394 K, at which the holes of the PC⁺ centers recombine with the electrons of the Ce²⁺ centers. Ivan Franko L’vov State University, 8, Kirilla i Mefodiya St., L’vov 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 545–547, July–August, 1997.     

Extra-liganding effects in Zn-octaethylporphyrin solutions in a temperature interval of 300-77 K

It is established experimentally for the first time that Zn-octaethylporphyrin in a solution of dried methyl cyclohexane is in unliganded form in the temperature interval of 293-77 K. This form is characterized by the shortest-wave position of absorption and luminescence spectra, the independence of the degrees of fluorescence and phosphorescence polarizations from the excitation wavelength, and high phosphorescence time (τ_T=126 μsec) and quantum yield (φp=0.085) at 77 K. Adding electrodonor components to the methyl cyclohexane or going over to alcohol-containing polar media leads to the formation of a monoliganded form of ZnOEP, for which we observe a bathochromic shift of ≈150–350 cm⁻¹ for Q(0,0) absorption and luminescence bands, a splitting of ≈50–100 cm⁻² for the Q(0, 0) absorption band, and phosphorescence quenching (τ_T=60 μsec, φp=0.05-0.03 at 77 K). The effects revealed are explained by a decrease in the symmetry of a ZnOEP molecule in extra liganding and by an increase in the probability of nonradiative activation for a T₁-state due to the extra ligand being involved in the exchange of electron-excitation energy and to the enhancement of a spin-orbital coupling as a result of the disturbance of the planarity, of a macrocycle. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 900–907, November–December, 1998.     

Luminescence of short-lived color centers induced in LiF crystals by a pulsed microwave discharge

A new phenomenon — intense luminescence of noncolored lithium fluoride (LiF) crystals excited by an electrodeless pulsed microwave discharge at the prebreakdown stage of development — is observed. This luminescence consists of the luminescence of short-lived aggregate F₂ and F ₃ ⁺ color centers at room temperature. It is shown that the density of short-lived color centers induced in the surface layer of LiF crystals by a microsecond microwave discharge reaches values of ∼10¹⁹−10²⁰ cm⁻³. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 163–167 (10 August 1997)     

Luminescence detection of multiphoton ionization-fragmentation of the molecular CrO 4 2− anions adsorbed on the surface of dispersed SiO2

It is shown that luminescence detection of multiphoton ionization-fragmentation of the molecular CrO ₄ ²⁻ anions adsorbed on the surface of dispersed SiO₂ is possible under excitation with the fundamental frequency of a Nd:YAG pulsed laser (λ=1.064 μm). The structure and the process of formation of the adsorbed complexes under thermal activation of the surface and the nature of luminescence transitions in CrO ₄ ²⁻ anions are studied in detail. It is shown that luminescence is excited as a result of the recombination of photoelectrons and ionized chromate ions. Multiphoton ionization of the ions occurs under three-photon resonance conditions. The resonance level is an antibonding state of the adsorption complex formed with the participation of an oxygen vacancy on the SiO₂ surface. The dynamics of the multiphoton luminescence excitation process includes autoionization (stimulated by intercomplex electronic excitation) in superexcited states, fragmentation of chromate anions, and annealing of surface oxygen vacancies. The rate equations for three-photon-resonance multiphoton ionization are studied. The cross sections for two-and one-photon transitions on the nonresonance steps of multiphoton absorption are obtained. It is concluded that the nonlinear polarizability of the donor-acceptor adsorption bond in “chromate anion-oxygen vacancy” complexes is very important. Zh. éksp. Teor. Fiz. 111, 1748–1774 (May 1997)     

Creation of excitons and defects in a CsI crystal during pulsed electron irradiation

Data presented on the influence of the temperature in the range 80–650 K on the spectral kinetics of the luminescence and transient absorption of unactivated CsI crystals under irradiation by pulsed electron beams (〈E〉=0.25 MeV, t _1/2=15 ns, j=20 A/cm²). The structure of the short-wavelength part of the transient absorption spectra at T=80–350 K exhibits features, suggesting that the nuclear subsystem of self-trapped excitons (STE’s) transforms repeatedly during their lifetime until their radiative annihilation at T⩾80 K, alternately occupying di-and trihalide ionic configurations. It is established that a temperature-induced increase in the yield of radiation defects, as well as F and H color centers, and quenching of the UV luminescence in CsI occur in the same temperature region (above 350 K) and are characterized by identical thermal activation energies (∼0.22 eV). It is postulated that the STE’s in a CsI crystal can have a trihalide ionic core with either an on-center or off-center configuration; the high-temperature luminescence of CsI crystals is associated with the radiative annihilation of an off-center STE with the structure (I⁻(I⁰I⁻ e ⁻))*. Fiz. Tverd. Tela (St. Petersburg) 40, 640–644 (April 1998)     

Luminescence and lasing properties of neodymium- and uranium-activated inorganic laser liquids

An attempt was made to describe and show the possibilities of new inorganic neodynium- and uranium-activated laser liquids: SO₂-GaCl₃-NdCl₄; SO₂Cl₂-GaCl₃-NdCl₃-UO₂Cl₂; POCl₂-MCl_n-NdCl₃-UO₂Cl₂ for development and synthesis of direct nuclear reaction-excited lasers. Luminescence data presented in the work were used to calculate the luminescence parameters of the laser liquids such as oscillator strengths f, probability of spontaneous radiation A, intermultiplet luminescence branching coefficient β, cross-section for induced radiation σ, luminescence decay time τ, quantum yield η, and others. It is shown that the oscillator strengths of the normal absorption bands of Na³⁺, which play the main part in the pumping processes, exceed the oscillator strengths of Na³⁺ for aqueous and many other nonaqueous systems. In the luminescence excitation spectra of the Na³⁺ ion, bands are isolated in the range 400–1000 nm atλ _rec =1.06 μm. With excitation, luminescence occurs through the⁴F_3/2→⁴I_{9/2,11/2.13/2} channels. Luminescence spectral data are related to the lasing parameters. The threshold lasing energy is∼18 J/cm³. For a resonator with mirros h₁=100% and h₂=20, 40, 56, and 80%, the lasing energy is∼20–120 MJ/cm³ in the pumping energy range 18–180 J/cm³. The differential efficiency is ∼0.2% The substantial angular radiation divergence (θ∼4·10⁻² rad) and strong thermostatic distortions that occur in the active element (dn/dT≈−1.9·10⁻⁴K⁻¹) are a disadvantage of laser liquids. It is shown that operation of neodymium- and uranium-activated inorganic liquid lasers is stable under the present conditions. A. I. Gertsen Russian State Pedagogical University, Moika Embankment, 48, St. Petersburg, 191186, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 607–619, September–October, 1997.     

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.     

Luminescence centers in ceramics of yttrium, scandium, and bismuth oxytungstates

An investigation is made of the luminescence spectra of Me₂WO₆ ceramics (Me=Y, Sc, Bi). The spectra were decomposed into elementary components by the Alentsev—Fock method. Radiation hands with a maximum at 3.02 eV in the Y₂WO₆ luminescence spectrum, at 2.8 eV in the ScWO₆ spectrum, and at 2.93 eV in the Bi₂WO₆ spectrum are assigned to the light emission of self-localized Frenkel excitons. The bands with maxima at 2.25 and 1.75 eV in the Y₂WO₆ spectrum, at 2.36 and 1.9 eV in the Sc₂WO₆ spectrum, and at 2.35 and 1.9 eV in the Bi₂WO₆ spectrum are related to oxygen vacancies. Translated from Zhurnal Prikladnoi Spektroskopii, Vol 67, No. 2, pp. 273–275, March–April, 2000.     

Photoluminescence of CaGa<Subscript>2</Subscript>S<Subscript>4</Subscript>:Pr Polycrystals

The photoluminescence (PL) and PL excitation spectra of CaGa₂S₄ polycrystals doped with praseodymium are studied in the regions of the activator absorption and the fundamental absorption of the host. It is found that the PL excitation spectrum consists of two regions: broadband absorption in the range of 200-380 nm corresponding to the fundamental absorption of the host and the narrow-band absorption of the dopant in the range of 430–515 nm. The luminescence spectra are different for different excitation wave-lengths, which occurs because Pr³⁺ ions substitute divalent cations occupying different crystallographic positions in the host crystal lattice.     

Luminescence centers in bismuth-containing oxytungstate ceramics

We have studied the photoexcitation and luminescence spectra of Bi₂WO₆, Y₂WO₆ and Y₂WO₆:Bi ceramics. We used the Alentsev-Fock method to decompose the spectra into elementary components. The emission bands with maximum at 2.93 eV in the luminescence spectrum of Bi₂WO₆, 3.02 eV in the luminescence spectrum of Y₂WO₆, and 2.95 eV in the luminescence spectrum of Y₂WO₆:Bi are assigned to luminescence of self-localized Frenkel excitons. The bands with maxima at 2.35 eV and 1.90 eV in the spectrum of Bi₂WO₆, 2.25 eV and 1.75 eV in the spectrum of Y₂WO₆, and 2.35 eV and 1.85 eV in the spectrum of Y₂WO₆:Bi are connected with oxygen vacancies. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 688–691, September–October, 2007.     

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.     

Anti-stokes luminescence of Zn<Subscript>0.6</Subscript>Cd<Subscript>0.4</Subscript>S solid solutions with adsorbed organic dye molecules and few-atom silver clusters

For microcrystals of Zn_0.6Cd_0.4S with adsorbed molecules of a number of organic dyes, we have observed sensitized anti-Stokes luminescence excited by radiation with wavelengths in the range 610–750 nm and flux density 10¹⁴–10¹⁵ photons/cm²·sec. The positions of the bands in the excitation spectra for such luminescence match those of the absorption spectra for the adsorbed dye molecules, which is evidence in favor of a cooperative mechanism for its appearance. We have shown that enhancement of the anti-Stokes luminescence is possible when silver atoms and few-atom clusters appear on the Zn_0.6Cd_0.4S surface in addition to the dye molecules. We hypothesize that its excitation in the latter case occurs as a result of two-photon optical transitions. These transitions occur sequentially, with transfer of an electron or the electronic excitation energy from the dye molecules to silver atoms and few-atom clusters adsorbed on the surface of Zn_0.6Cd_0.4S, creating deep localized states in the bandgap with photoionization energies 1.80–2.00 eV. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 617–621, September–October, 2007.     

Explosive luminescence of silver azide

Spectroscopic-kinetic investigations of the luminescence accompanying the explosive decomposition of silver azide are performed. A new phenomenon is observed: predetonation luminescence. A comparison of the predetonation luminescence spectrum with the band structure is in agreement with a model in which the exothermic reaction 2N ₃ ⁰ →N₆ provides the energy for the explosion. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 2, 101–103 (25 July 1997)     

Radiation-stimulated changes in the transmission of chalcogenide glasses of As2S3−Ge2S3

The radiative-optical properties of chalcogenide glass-like semiconductors of the As₂S₂−Ge₂S₃ system in the region of a topological 2D-3D-phase transition are investigated. It is shown that γ-irradiation of samples by an absorbed dose of 4.4 · 10⁶ Gy leads to a longwave shift of their optical-transmission edge in the spectrum. The effect observed depends on the structural type of the glasses investigated and changes considerably near the 2D-3D-phase transition. Two components of the transmission-edge shift are detected: a static component, which remains unchanged for a long time after irradiation of the samples, and a dynamic one, which gradually fades in 2–3 months. It is suggested that the microstructural mechanism of these changes is attributable to processes of coordination defect formation in the structural skeleton of the samples. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, pp. 657–660, September–October, 1999.