Showing papers by "Martin Nikl published in 2001"
TL;DR: In this paper, electron traps based on regular Pb sites perturbed by oxygen vacancies have been revealed and studied by electron spin resonance (ESR) and thermally stimulated luminescence (TSL) measurements.
Abstract: Electron traps based on regular Pb sites perturbed by oxygen vacancies ${(V}_{\mathrm{O}})$ in high purity undoped ${\mathrm{PbWO}}_{4}$ have been revealed and studied by electron spin resonance (ESR) and thermally stimulated luminescence (TSL) measurements. Detailed analysis of ESR spectra parameters $(g$ factor, hyperfine, and superhyperfine structures) along with the variation of the concentration after annealing in inert and oxygen atmospheres had shown that revealed centers are ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ complexes. The ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers are created in two ways: (i) by direct trapping of the electrons from the conduction band under x-ray or ultraviolet irradiation at $T=60 \mathrm{K};$ (ii) by retrapping of electrons freed from unperturbed $({\mathrm{WO}}_{4}{)}^{3\ensuremath{-}}$ centers after irradiation at $Tl40 \mathrm{K},$ followed by heating at $T=60 \mathrm{K}.$ Above $T\ensuremath{\approx}180 \mathrm{K},$ ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers are thermally ionized, giving rise to a TSL glow peak due to the recombination of freed electrons with localized holes. The emission spectrum of the TSL features one band peaking at around $2.5 \mathrm{eV}.$ The temperature dependence of both TSL and ESR intensities has been analyzed using a first order recombination model: the thermal ionization energy of ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers turns out to be $0.55 \mathrm{eV}.$ The role of ${\mathrm{Pb}}^{+}\ensuremath{-}{V}_{\mathrm{O}}$ centers in the processes of carrier trapping and recombination of nonequilibrium carriers in the ${\mathrm{PbWO}}_{4}$ lattice is briefly discussed.
70 citations
41 citations
TL;DR: In this article, the absorption, emission and excitation spectra of small CsPbBr 3 aggregates (nanocrystals), thermally created in CsBr:Pb single crystals, have been studied at 4.2-300 K. A strong influence of crystal structure imperfections, lead concentration, crystal quenching conditions as well as annealing temperature and duration has been detected and analysed.
41 citations
TL;DR: Sensitization role of Gd 3+ ions in energy transfer processes in radio and photo-luminescence is described for Tb 3+ -doped and Gd-enriched Na x Gd y phosphate glasses as discussed by the authors.
40 citations
TL;DR: In this paper, the influence of different doping ions on the emission and scintillation characteristics of PbWO 4 scintillator was studied, and the leading emission lines were obtained at 543, 641 and 602 nm, respectively.
32 citations
TL;DR: In this paper, the radio-, photo-and thermoluminescence properties of Gd-free glass matrix have been investigated and it has been shown that Gd 3+ -sublattice becomes frozen below 10-15 K due to local field fluctuations in the glass matrix.
31 citations
01 Mar 2001-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a new heavy and radiation-hard Cherenkov radiators based on PbWO4 was proposed, which has been established as one of the heaviest and radiation hard scintillators in these years by means of purifying raw materials, doping with appropriate trivalent ions, etc.
Abstract: We propose a new heavy and radiation-hard Cherenkov radiators based on PbWO4, which has been established as one of the heaviest and radiation-hard scintillators in these years by means of purifying raw materials, doping with appropriate trivalent ions, etc. Heavy doping with trivalent ions such as Gd3+(or La3+) by more than 3 at%(5 at%) in the melt, considerably reduces the scintillation light intensity to a level as low as or lower than the Cherenkov light intensity, by keeping the excellent radiation hardness and causing no significant degradation in the short wavelength cutoff in the transmittance spectra.
29 citations
11 Jun 2001-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, the tetravalent-ion doping was shown to be as efficient as or even more efficient than trivalent ion doping in improving PbWO 4 scintillator.
Abstract: In our previous papers we reported that La 3+ , Gd 3+ , Y 3+ , and Lu 3+ dopings significantly improve the optical and scintillation characteristics, including radiation hardness, of PbWO 4 single crystals. The hypothesis of Pb 2+ deficiency in the grown crystals and its charge compensation by the mentioned trivalent ions occupying the Pb 2+ sites has been proposed to explain the observed improvement. Under such assumption, tetravalent-ion doping may be as efficient as or even more efficient than trivalent-ion doping in improving PbWO 4 scintillator. Recently we extended the dopant ions to stable tetravalent ions (Th 4+ , Zr 4+ ) and some other ions (Ce 3+,4+ , Sb 3+,5+ , Mn 2+ ). We have found that the tetravalent-ion (Th 4+ ) doping gives similar improvement compared with the trivalent-ion doping in consistency with the expectation mentioned above. The ions with two different possible charge states (Ce 3+,4+ , Sb 3+,5+ ) gave finite but much less improvement than the trivalent and tetravalent ions. Ce 3+,4+ doping reduced the light yield significantly. Annealing of undoped PWO in PbO vapour was also studied to examine the possibility of reducing the Pb 2+ deficiency
28 citations
TL;DR: Luminescent aggregates of various types have been produced in quenched CsI:Pb single crystals by their annealing in vacuum at temperatures from 220 to 370°C for 18 to 137 h.
Abstract: Luminescent aggregates of various types have been produced in quenched CsI:Pb single crystals by their annealing in vacuum at temperatures from 220 to 370°C for 18 to 137 h It has been found that the relative concentrations of different aggregates depend on thermal treatment conditions Their optical characteristics obtained at 42-300 K have been compared with the corresponding characteristics of CsPbI 3 and Cs 4 PbI 6 single crystals as well as with the characteristics of CsPbI 3 3 and Cs 4 PbI 6 -type aggregates in CsI-PbI 2 thin films The absorption band located near 411 nm and the emission bands peaking at 465 535 and 600 nm have all been ascribed to the CsPbI 3 -type aggregates dispersed in a C'sl single crystal matrix The emission band peaking at 435 nm and the corresponding excitation bands at 362 and 288 nm have been ascribed to the Cs 4 PbI 6 -type aggregates The mechanism of the creation of aggregates in a CsI:Pb crystal has been discussed
26 citations
TL;DR: In this paper, the emission-band shape of tetrahedral complexes with an excited state consisting of two closely lying triplet states is numerically calculated within the semiclassical approach using Monte Carlo integration.
Abstract: Tetrahedral complexes with an excited state consisting of two closely lying triplet states are considered. The full interaction Hamiltonian, including ligand field, Jahn-Teller, pseudo-Jahn-Teller, and spin-orbit interactions is constructed. The emission-band shape is numerically calculated within the semiclassical approach using Monte Carlo integration. The results of this numerical analysis are applied to the ${\mathrm{PbWO}}_{4}$ system. Comparison with experimentally obtained spectra shows that this theory explains the observed triple-peak structure.
26 citations
TL;DR: In this article, the influence of different doping ions on the emission and scintillation characteristics of PbWO4 scintillator was studied, and Tb3+ and Pr3+ doping results in dominant emission lines at 543 and 602 nm with decay times of about 650 and 61 μs at 295 K, respectively.
TL;DR: In this paper, an anisotropic quantum dot growth has been proposed for the explanation of the structural character of the spectra and their temperature dependences and its dependence on the annealing temperature and time duration.
Abstract: Absorption and luminescence characteristics of CsPbCl3-like quantum dots in as-received as well as in quenched and subsequently annealed CsCl : Pb crystals have been studied with a spectral resolution of 0.2 nm at temperatures 12–300 K. A complicated structure of absorption, emission and excitation spectra has been found and its dependence on the annealing temperature and time duration is examined. The temperature dependences of the intensities, positions and halfwidths of the spectral bands have been measured. An anisotropic quantum dot growth has been proposed for the explanation of the structural character of the spectra and their temperature dependences.
TL;DR: In this paper, a wide class of experimental fits were provided in support of a model previously proposed to explain anomalous nonexponential decay of the slow luminescence component of Pb2+ centers in alkali halide crystals.
01 Dec 2001-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, the effect of 60 Co irradiation on the optical properties of selected phosphate and silicate-based scintillating glasses was investigated by transmission measurements performed at room temperature in the UV-Visible part of the spectra.
Abstract: The effect of 60 Co irradiation (1–250 Gy) on the optical properties of selected phosphate and silicate-based scintillating glasses was investigated by transmission measurements performed at room temperature in the UV–Visible part of the spectra. Samples doped with rare-earth ions (Ce 3+ , Tb 3+ as emission centres, and Gd 3+ as an additional constituent in certain compositions) have been studied. The results are discussed taking into account the possible influence of different glass compositions on radiation induced colour centres.
TL;DR: In this paper, optical properties of polycrystalline thin films grown by physical vapour deposition were determined by absorption, emission and decay kinetics measurements, and the optical features of these nanostructures were found to be in agreement with reported band-structure calculations.
TL;DR: In this paper, the optical properties of CsPbCl3 and Cs4pbCl6 nanostructures were determined using x-ray diffraction spectroscopy.
Abstract: Ternary nanophases of CsPbCl3 and Cs4PbCl6 were evidenced in co-evaporated CsCl–PbCl2 thin films using x-ray diffraction spectroscopy. A morphological study by atomic force microscopy revealed the granular nature of the films consisting of the grains of about 150 nm size. The optical properties of CsPbCl3 and Cs4PbCl6 nanostructures were determined. CsPbCl3 is a wide gap semiconductor with direct band transitions and a pronounced Wannier free exciton emission round 418 nm at 5 K with a very small Stokes shift. Cs4PbCl6 is characterized by the auto-localized exciton emission around 365 nm. In both cases, the optical features are closely similar to the bulk ternary crystals which were reported earlier.
TL;DR: In this article, the authors investigated the origin and structure of the relaxed excited states responsible for the 3.33, 2.8 and 2.43 eV emission bands of CsBr:Pb.
Abstract: Absorption, emission and excitation spectra, polarization and decay kinetics of luminescence and their temperature dependences have been studied at 4.2-300 K for several CsBr:Pb samples with various lead concentrations. The origin and structure of the relaxed excited states responsible for the 3.33, 2.8 and 2.43 eV emission bands have been discussed. It has been concluded that the relaxed excited state model proposed for Tl + -doped caesium halides and CsCl:Pb is not valid in case of CsBr:Pb. To establish the origin of the relaxed excited states in a CsBr:Pb crystal, the luminescence characteristics of CsBr:Pb have been compared with those reported for Cs 4 PbBr 6 , PbBr 2 and CsPbBr 3 bulk crystals. It has been assumed that owing to a strong interaction between Pb 2+ and Br- ions, the molecular-like states, which are similar to the excited levels of some stable lead-related compounds, are responsible for the luminescence of CsBr: Pb crystals.
TL;DR: In this article, the authors analyzed the scintillation characteristics such as light yield and decay time and the radiation damage of Ce-doped Bi4Si3O12 (BSO) single crystals grown by the vertical Bridgman method.
Abstract: We have analyzed the scintillation characteristics such as light yield and decay time and the radiation damage of Ce-doped Bi4Si3O12 (BSO) single crystals grown by the vertical Bridgman method. Ce was doped into BSO at 0.1, 0.2 and 0.4 at.% and the grown crystals were analyzed. For the Ce doping at 0.1 at.%, the light yield decreased by 40% while the average decay constant decreased by 20% (from 105 ns to 86 ns). Radiation damage was assessed by measuring the optical transmittance before and after irradiating the crystals with 60Co γ-rays for a maximum accumulated dose of 107 rad. Significant improvement was found for the radiation hardness of Ce-doped BSO.
TL;DR: In this article, the optical properties of Pb2+-based ternary nanophases were determined in co-evaporated CsPbX3 and Cs4pbX6 nanostructures using X-ray diffraction spectroscopy (XRD).
Abstract: The creation of Pb2+-based ternary nanophases was evidenced in co-evaporated CsX-PbX2 (X = Cl, Br, I) thin films using X-ray diffraction spectroscopy (XRD). The optical properties of CsPbX3 and Cs4PbX6 nanostructures were determined. CsPbX3 (X = Cl,Br) are wide gap semiconductors with direct band transitions and a pronounced Wannier free exciton emission showing subnanosecond decay times and very small Stokes-shift. On the contrary, it is supposed that, in CsPbI3, the auto-localization of the exciton state results in a broad and much slower emission with large Stokes shift. Cs4PbX6 is characterized by the auto-localized exciton emission in the near UV/violet spectral region and two component decay kinetics closely similar to that of Pb2+ emission centers in KX:Pb2+ (X = Cl, Br, I).
TL;DR: In this paper, optical absorption, photo-and thermo-luminescence measurements were performed on (NaPO3)x(GdPO4)y(TbPO4z (x=60 − 77 mol % ; y=20 − 30 mol %; z=3 − 10 mol %) glasses.
Journal Article•
Journal Article•
TL;DR: In this article, the absorption and luminescence of divalent lead both as an impurity and as a cation in lead chlorides are obtained, taking into account the very low local symmetry in all measured lead compounds.