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 recombination processes and luminescence in Li<Subscript>6</Subscript>(Y,Gd,Eu)(BO<Subscript>3</Subscript>)<Subscript>3</Subscript> crystals

The thermally stimulated recombination processes and luminescence in crystals of the lithium borate family Li₆(Y,Gd,Eu)(BO₃)₃ have been investigated. The steady-state luminescence spectra under X-ray excitation (X-ray luminescence spectra), the temperature dependences of the X-ray luminescence intensity, and the glow curves for the Li₆Gd(BO₃)₃, Li₆Eu(BO₃)₃, Li₆Y_0.5Gd_0.5(BO₃)₃: Eu, and Li₆Gd(BO₃)₃: Eu compounds have been measured in the temperature range 90–500 K. In the X-ray luminescence spectra, the band at 312 nm corresponding to the ⁶ P _J → ⁸ S _7/2 transitions in the Gd³⁺ ion and the group of lines at 580–700 nm due to the ⁵ D ₀ → ⁷ F _J transitions (J = 0–4) in the Eu³⁺ ion are dominant. For undoped crystals, the X-ray luminescence intensity of these bands increases by a factor of 15 with a change in the temperature from 100 to 400 K. The possible mechanisms providing the observed temperature dependence of the intensity and their relation to the specific features of energy transfer of electronic excitations in these crystals have been discussed. It has been revealed that the glow curves for all the crystals under investigation exhibit the main complex peak with the maximum at a temperature of 110–160 K and a number of weaker peaks with the composition and structure dependent on the crystal type. The nature of shallow trapping centers responsible for the thermally stimulated luminescence in the range below room temperature and their relation to defects in the lithium cation sublattice have been analyzed.     

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.     

Thermally and photostimulated recombination processes in PbWO4 crystals at low temperatures

We have studied thermally and photostimulated recombination processes in PbWO₄ crystals in the temperature interval 90–295 K. We have shown that after x-ray excitation of the crystal at 90 K, the thermally stimulated luminescence curve shows a relatively intense peak at 110 K and weak peaks at about 173, 191, and 232 K. Exposure of the PbWO₄ crystal to IR radiation after excitation by x-ray photons leads to the appearance of photostimulated flash luminescence, a significant decrease in the intensity of the 110 K peak, and a shift of that peak to the 116 K region. But long-wavelength illumination has less of an effect on the intensity and position of the higher temperature peaks. It is assumed that F⁻ centers are formed in the PbWO₄ crystal at 90 K during x-ray exposure. The thermal light sum released by IR illumination in the temperature region 90–150 K has a maximum at ≈108 K. The nature of this maximum is connected with the complex centers [Pb³⁺ + (WO_3-F⁻)]. Optical and thermal degradation of these centers leads to the appearance of emission in the green region of the localized exciton spectrum.     

Energy Levels in the Forbidden Band of the Bi4Ge3O12 Ceramics

Thermally stimulated luminescence in the Bi₄Ge₃O₁₂ ceramics and also in the ceramics of the parent components Bi₂O₃ and GeO₂ is investigated. The similarity of the curves of the thermally stimulated luminescence in bismuth germanate with the structure of eulytine Bi₄Ge₃O₁₂ and sillenite Bi₁₂GeO₂₀ is explained. The relation of the thermally stimulated luminescence band in Bi₄Ge₃O₁₂ (with a maximum at 143 K) to the disruptions in the germanium sublattice and of the thermally stimulated band (with a maximum at 187 K) to the recombination processes in the bismuth sublattice is shown. It has been established that the light sum in the Bi₄Ge₃O₁₂ ceramics is stored most effectively upon excitation by light in an energy region of 4.4 eV.     

Thermally stimulated emission of electrons and photons in nonlinear LiB3O5 crystals

The results of an investigation of the thermally stimulated emission of electrons and photons in lithium triborate single crystals are presented. The investigation is performed mainly by simultaneously measuring the thermally stimulated emission of electrons and photons after various radiation treatments. In particular, the thermally stimulated exoelectron emission of LiB₃O₅ crystals is discovered for the first time and studied in detail. An analysis of the experimental results reveals two new trapping centers. It is established that the thermal annealing of these centers at 450 and 515 K makes a contribution only to the exoelectron emission. It is postulated that a field fluctuation process, which lowers the potential barriers of the trapping centers, takes place in LiB₃O₅ at 100–140 K. This process is attributed to thermally stimulated relaxation of the radiation-induced charge. A significant dependence of the parameters of the thermally stimulated processes in LiB₃O₅ on the parameters of the radiation treatment is discovered. Zh. Tekh. Fiz. 67, 121–125 (July 1997)     

Thermally stimulated luminescence of bismuth germanate ceramics with the benitoite,eulitine, and sillenite structures

Thermally stimulated luminescence (TSL) of Bi₂Ge₃O₉, Bi₄Ge₃O₁₂, and Bi₁₂GeO₂₀ and the primary components Bi₂O₃ and GeO₂ was studied under x-ray excitation. Thermal activation energies and frequency factors of trapping centers in the studied ceramics were determined. The relationships of TSL bands of the studied ceramics with maxima at 141–145 and 166–170 K and damage to the Ge sublattice and of TSL bands with maxima at 104–110 and 180–190 K and recombination processes in the Bi sublattice were demonstrated. Recombination processes causing luminescence upon nonequilibrium charge carrier release from trapping centers occur in structural complexes of similar configuration that contain the Bi ion in a nearest environment of O atoms. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 359–364, May–June, 2008.     

Tunneling luminescence of Y2O3 and Sc2O3 ceramics

In the present work we investigate the tunneling luminescence (TL) of Y₂O₃, Y₂O₃:Eu, and Sc₂O₃ ceramics. From an analysis of the decay kinetics of the TL it is established that the recombinational processes are described by a model involving recombination with a complex interaction. In addition, using the method of partial light sums, we show that in the ceramics investigated the mechanisms of TL are the same and the majority of radiation-induced defects in pairs are removed to distances exceeding the radius of effective tunneling transitions with a time constant of 10–100 sec. In the Y₂O₃:Eu ceramics the distances between defects decrease. TL occurs in pairs whose electron component is F-centers that are thermally released at 176 K in the Y₂O₃ ceramics and 200 K in the Sc₂O₃ ceramics. The hole components of tunneling pairs are associated with centers that are thermally released at 110 and 122 K in the Y₂O₃ ceramics and at 121 and 146 K in the Sc₂O₃ ceramics. To whom correspondence should be addressed. I. Franko Lvov State University, 50, Dragomanov Str., Lvov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 649–651, September–October, 1999.     

Storing energy in lithium fluoride crystals irradiated with femtosecond laser pulses

The release of energy in the form of the light sum of thermally stimulated luminescence (TSL), stored under conditions of self-focusing and the multiple filamentation of femtosecond laser radiation during the interaction between model wide-bandgap dielectric crystals of lithium fluoride is studied. It is shown that F₂ color centers are important centers of emission in the TSL process.     

Thermoluminescence of corundum containing anion defects following ultraviolet laser and x irradiation

The thermoluminescence of single crystals of corundum containing anion defects following x-ray and laser excitation is investigated. Its features in the luminescence bands of F, F⁺, and Cr³⁺ centers are studied. Synchronous measurements of the thermoluminescence and thermally stimulated exoelectron emission are performed by the fractional glow technique following x-ray and laser excitation of the samples. It follows from the results obtained that several traps are active in the temperature range of the principal dosimetric peak (400–500 K). The spectral sensitivity curve contains maxima corresponding to absorption bands of F, F⁺, and Al _i ⁺ centers. A possible mechanism for the recombination luminescence of F centers is discussed. It is found that the material exhibits high sensitivity to small doses of ultraviolet laser radiation. Zh. Tekh. Fiz. 67, 72–76 (July 1997)     

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.     

Kinetics of thermally stimulated recombination processes in lithium borate crystals

This paper reports on the results of the experimental and theoretical investigations of thermally stimulated recombination processes in crystals of the lithium borates Li₂B₄O₇ and LiB₃O₅. For both types of crystals, the measurements of thermally stimulated luminescence curves, spectra, and temperature dependences of the intensities of steady-state X-ray luminescence have been performed in a single experimental cycle. In the framework of a unified model for the Li₂B₄O₇ and LiB₃O₅ crystals, the thermally stimulated recombination processes have been calculated and the obtained results have been interpreted talking into account all available experimental data.     

Space-charge relaxation and electrical conduction in?K0.5Na0.5NbO3 at high temperatures

Sodium potassium niobate K_0.5Na_0.5NbO₃(KNN) ceramic was synthesized by a solid-state technique. The X-ray diffraction of the sample at room temperature showed a monoclinic phase. The real part (ε′) and imaginary part (ε″) of dielectric permittivity of the sample were measured in a frequency range from 40 Hz to 1 MHz and in a temperature range from 350 to 850 K. The ε′ deviated from Curie–Weiss law above 702 K, due to additional dielectric contributions resulting from universal dielectric response and thermally activated space charges at high temperatures. This anomaly arose from a Debye dielectric dispersion that slowed down following an Arrhenius law. We have established a link between the dielectric relaxation and the conductivity.     

Luminescence properties of Nd<Superscript>3+</Superscript>-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in organic media

Nd³⁺-doped yttrium oxide nanoparticles (Y₂O₃:Nd) with cubic phase were obtained successfully by a glycine-nitrate solution combustion method. The results of Fourier transform infrared spectra (FTIR) showed that the –OH groups residing on the nanoparticles surfaces were reduced effectively by modifying with capping agent. The modified Y₂O₃:Nd nanoparticles displayed good monodispersity and excellent luminescence in N,N-dimethylformamide (DMF) solvent. Some optical parameters were calculated by Judd–Ofelt analysis based on absorption and fluorescence spectra. A relative large stimulated emission cross section, 1.7×10⁻²⁰ cm², of the ⁴F_3/2→⁴I_11/2 transition was calculated. Theses results show that the modified Y₂O₃:Nd nanoparticles display good luminescence behavior in organic media.     

Spontaneous and stimulated red luminescence of Lu2O3: Eu nanocrystals

The spectra of spontaneous and stimulated luminescence of Lu₂O₃: Eu (7 at %) nanopowders at different optical pumping intensities have been investigated. The obtained results—changes in the shape of the red luminescence spectra and in the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions—indicate the onset of superluminescence with an increase in the excitation power. It has been found that an increase in the optical pumping intensity leads to a decrease in the luminescence decay time of the Lu₂O₃: Eu (7 at %) phosphor in the stimulated luminescence regime and to an increase in the quantum efficiency of red luminescence with a maximum at 611 nm.     

Luminescence centers in α-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics

Luminescence photoexcitation spectra of α-Bi₂O₃ ceramics are investigated. Luminescence spectra were deconvoluted into fundamental components using the Alentsev-Fok method. It is established that the luminescence spectra of α-Bi₂O₃ ceramics consist of three fundamental bands with maxima at 2.75, 2.40, and 1.97 eV. A comparison of the results with those from an investigation of luminescence of various modifications of bismuth oxide and bismuth germanates suggests that luminescence of these compounds is caused by radiation processes that occur in structural complexes that contain the bismuth ion in a nearest oxygen environment. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 672–676, September–October, 2008.     

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.     

Dosimeter properties of Ce and Eu doped LiCaAlF6

Optical, scintillation properties, optical stimulated luminescence, and thermally stimulated luminescence of Ce 1, 3, and 5% doped and Eu 1, 1.5, and 2% doped LiCaAlF₆ crystals fabricated by Tokuyama Corp. were investigated. In transmittance, absorption was proportional to dopant concentrations and typical optical quantum yield of Ce and Eu-doped LiCaAlF₆ were 40 and 100%, respectively. Scintillation wavelength and decay time profiles were investigated under X-ray irradiation. Ce³⁺ and Eu²⁺ 5d-4f luminescence appeared around 300 nm and 370 nm with typical decay time of 40 ns and 1.5 μs, respectively. Optically stimulated luminescence of Ce-doped ones appeared under 405 nm stimulation with detectable intensity while those of Eu doped ones were quite weak. Thermally stimulated luminescence of Ce- and Eu-doped LiCaAlF₆ were enough strong and they exhibited good response function from 1 to 1000 mGy exposure.     

Anomalies in the physical properties of the α form of bismuth oxide

Several of the physical properties of α-Bi₂O₃ have been studied in the temperature region above room temperature: the thermal expansion, the thermally stimulated current, the permittivity, the electrical resistance, and the specific heat. X-ray diffraction measurements and a thermogravimetric analysis have also been carried out. Several unusual properties in the physical properties of bismuth oxide have been detected in the temperature interval 450–570 K: exothermic maxima on the DTA and DSC curves, a small maximum and a sharp increase of the permittivity of the single crystal, a jump and a change of sign in the thermally stimulated current, and a sharp falloff of the electrical resistance of ceramic samples. At the same time, no appreciable changes in the monoclinic structure of α-Bi₂O₃ have been recorded in the indicated temperature interval. Fiz. Tverd. Tela (St. Petersburg) 39, 865–870 (May 1997)     

Tunneling recombination luminescence in Na2O · 3SiO2 glass

The recombination luminescence exhibited by Na₂O · 3SiO₂ glass in the spectral region from 1.5 to 5.0 eV, after excitation by X-rays or quanta with energies ranging from 5.8 to 6.2 eV, consists of thermally stimulated and tunneling components. The tunneling luminescence band shape depends on the population of various depth traps.