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.     

Mechanism of photoluminescence excitation of Mn<Superscript>2+</Superscript> ions in ZnS crystals

The mechanisms of photoluminescence excitation of Mn²⁺ ions in ZnS crystals have been investigated on the basis of complex analysis of the temperature dependences of the photoluminescence and photoluminescence-excitation spectra of ZnS:Mn crystals. The activation energy of a manganese luminescence center was estimated at E_a = 0.17 ± 0.05 eV. It is shown that E_a represents an energy band with a width ΔE_a = 0.1 eV, within which a manganese luminescence center can experience radiationless recombination. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 788–793, November–December, 2005.     

Luminescence excitation spectra and characteristics of luminescence centers with overlapping absorption bands

For an ensemble of different types of luminescence centers with overlapping absorption bands, with no restrictions on the optical densities, we have obtained relations describing the luminescence excitation spectra for each type of center. We consider transformations of the relations in some limiting cases. We suggest a procedure for using the equations obtained to determine the characteristics of the luminescence centers. Some of these procedures have been experimentally implemented in study of intrinsic radiation color centers in lithium fluoride crystals. We have determined the ratios of the luminescence quantum yields for F₂ and F₃⁺ color centers, and we have observed that a major role is played by nonradiative transitions in deactivation of the first excited singlet state of F₃⁺ centers. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 365–371, May–June, 2008.     

Analytical relations for luminescence intensities accounting for reabsorption

Mathematical relations defining distortions from true values of photoluminescence intensities that arise during measurements due to absorption at the luminescence frequencies are derived for various experimental designs. The adequacy of the derived relations is confirmed by special experiments. The relations allow one to define correctly the contours, widths, and maximum frequencies of luminescence bands of absorbing media and to deduce absorption coefficients of substances from luminescence measurements. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 788–795, November–December, 2008.     

Luminescence of aggregate centers in CsBr:Eu2+ single crystals

We have used the Bridgman method to grow CsBr:Eu²⁺ single crystals, adding an activator to the mix in the form of Eu₂O₃ in amounts of 0.0125, 0.0250, and 0.0500 mole %. At T = 300 K, we studied the absorption spectra, the photoluminescence (PL) spectra, and the photostimulated luminescence (PSL) spectra of the grown crystals. We have established that the structure of the photoluminescence and photostimulated luminescence centers in crystals grown from the CsBr:Eu₂O₃ mix includes isolated dipole centers Eu²⁺-V_Cs, emitting in bands with maxima at 432 nm and 455 nm respectively, and in crystals grown at activator concentrations of 0.025 and 0.050 mole % they also include aggregate centers (AC) based on CsEuBr₃ nanocrystals with emission bands at 515 m and 523 nm. We have shown that the maximum concentration of aggregate centers of the CsEuBr₃ nanocrystal type in CsBr:Eu²⁺ crystals is achieved for an activator content in the mix within the range 0.01–0.05 mole %. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 359–362, May–June, 2006.     

Excitation spectra and structure of luminescence centers of manganese ions in single crystals of zinc sulfide

We investigate the photoluminescence excitation spectra in ZnS:Mn single crystals at room temperature and at the temperature of liquid nitrogen with a different concentration of Mn²⁺ ions. The strongest bands peaking at 557, 578, 600, and 637 nm are associated with a different position of the Mn ion in the lattice of the crystals under investigation. The difference obtained in the excitation spectra can be explained by the resonance transfer of energy between the Mn ions. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 208–210, March–April, 2000.     

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.     

Analysis of the latent structure of luminescence and absorption spectra of thallium complexes

Comprehensive investigations of luminescence, excitation, and absorption spectra as well as of the luminescence kinetics of a frozen LiCl-Tl⁺ solution are carried out. It is established that the luminescence spectrum consists of four components. One component is caused by luminescence of the matrix and the remainder by luminescence of one luminescence center, namely, by the saturated complex of thallium TlCl₂(H₂O)Cl₄. The absorption spectrum consists of three components. Their parameters have been evaluated. Each component of the luminescence spectrum is excited in several components of the absorption spectrum. It is found that the luminescence spectrum components and their intrinsic absorption bands are located differently on the frequency axis. These data are similar to those obtained for other activated solutions of electrolytes. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 75–78, January–February, 2000.     

Luminescence centers in cubic boron nitride

Complex and multiband photoluminescence spectra for GB and HBN centers in single crystals of cubic boron nitride (cBN) were recorded in the wavelength ranges 385–400 nm and 365–395 nm and the nature of these centers was studied. The use of models involving resonance vibrations and strongly shifted configuration diagrams for the electronic ground state and excited state made it possible to associate formation of the GB-1 center with the presence of tungsten impurity in cBN. It was established that the HBN band in the 300–350 nm range of the cathodoluminescence spectra of cBN polycrystals, single crystals, and micropowders is associated with luminescence centers present in microinclusions of graphite-like boron nitride (hBN). The nature of the hBN band is tentatively interpreted within the model of recombination of donor and acceptor defects in hBN: respectively nitrogen vacancies and carbon atoms in positions substituting for nitrogen. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 241–246, March–April, 2007.     

On some UV emissions in calcite

Two UV emission bands have been found under UV excitation in hydrothermal synthetic calcite crystals at 347 and 385 nm. Their temperature dependence can be explained in terms of transfer through the Auger effect toward a well-known center absorbing near 350 nm, which can now be described as a killer of luminescence in calcite at room temperature.     

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.     

Recombination radiation of ZnTe crystals with ap-n junction formed by the laser doping technique

Radiative recombination is studied in ZnTe-based diodes produced on the basis of a p–n junction formed by laser doping of crystals with an Al donor impurity. The luminescence spectra obtained in the case of excitation of the diodes by direct current with a density of 3 A/cm² and the photoluminescence spectra at 80 and 300 K are measured. A comparison of the photoluminescence spectra of the p-ZnTe substrate and the electroluminescence spectra at 80 K suggests that radiative recombination in the diodes occurs in the Al-doped region of the crystal. At 80 K in the electroluminescence spectra of the diodes, a band, unknown previously, with the position of the energy maximum at 2.276 eV was observed. This band can be assigned to radiative transitions between the donor level of the al atom and the valence band. For the first time, long-wave bands assigned to participation of deep, compensatory centers were not found in radiative recombination of ZnTe-based diodes. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 382–386, May–June, 1998.     

Photoluminescence of AgGaTe2 single crystals

The temperature dependence of the photoluminescence spectra of AgGaTe₂ single crystals obtained by the Bridgman-Stockbarger method is investigated within the temperature range 10-300 K. The emission bands associated with donor-acceptor recombination and free and bound excitons are detected. The bonding energy of the free exciton and the forbidden gap of the crystals at 10 K are calculated. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 222–224, March–April, 2000. This work is partially sponsored by the British Royal Society, INTAS (grant No. 634), and EPSRC (grant GR/L 62757).     

Luminescence of europium and ytterbium ions in strontium hexaborate

We have studied the luminescent properties of Eu^2+/3+ and Yb²⁺ ions in strontium hexaborate SrB₆O₁₀ for excitation in the 120–400 nm region. The luminescence spectra of Ln²⁺ ions in SrB₆O₁₀ consist of overlapping bands in the 370–520 nm region, due to 5d → 4f transitions at several nonequivalent centers. In the excitation spectra, besides the bands associated with 4f → 5d transitions in the Ln²⁺ ions, we also observe a band in the 135–160 nm region due to the transitions O(2p) → B(2s,2p) within the borate anions. The luminescence of the Eu³⁺ ions is excited most efficiently in the region of the Eu³⁺ charge transfer band (λ_max = 226 nm). The results obtained are compared with data for Ln in other strontium borates. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 770–774, November–December, 2006.     

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.     

Dependence of the spectroscopic properties of pentauranylfluoride crystals on temperature in the range from 4.2 to 40 K

Using the configuration interaction model, we investigate the dependence of the shape, half-width, and position of the phononless lines (PL) in absorption and luminescence spectra of K₃UO₂F₅ and Rb₃UO₂F₅ crystals in the region 4.2–40 K. It is established that a Stokes shift in combining electron states leads to a nonsymmetric distortion in the Gauss shape of thePL. The temperature broadening of the PL is mainly associated with a change in the population of the initial states of oscillators (of the ground state for absorption and the 1 st excited state for luminescence), while a shift in maxima of the PL is caused by the forbidden 1 st electron transitions in complex uranyl compounds and is determined by the nonlinear electron-phonon interaction. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 824–827, November–December, 1999.     

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.     

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 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 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.