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1

New High Performance Scintillators Based on Re-Activated Insulator Materials

100%

Wojtowicz A.

Acta Physica Polonica A

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1996

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vol. 90

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issue 1

215-222

EN

In this paper we address the problem of the host-to-ion energy transfer in some RE-activated wide band gap materials excited by ionizing radiation. We argue that, despite the expected self-localization of holes, the dominant mechanism in efficient materials involves sequential trapping of both charge carriers (holes and electrons) by an activating RE-ion followed by a radiative recombination via the ion producing scintillation light. Selected experimental results are presented to illustrate how various energy transfer processes manifest themselves in the spectroscopy of scintillator materials. Experimental results combined with simple considerations are used to identify these RE-ions which are likely to act as hole or electron traps in tri- and difluorides, thus initiating the recombination sequence leading to efficient scintillation.

2

Physics of Solid-State Laser Materials

100%

Wojtowicz A.

Acta Physica Polonica A

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1991

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vol. 80

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issue 2

193-205

EN

A survey of the physical properties of solid state materials activated with d^{2}, d^{3} and d^{8} transition metal ions is presented in the context of tunable laser operation. An emphasis is put on common characteristics of all three systems, like a strong electron-phonon coupling and similar electronic structures. The conditions necessary to obtain a tunable operation and to avoid an overlap of the excited state absorption and emission are formulated. It is shown that the d^{3} configuration system has the largest range of allowed values of the crystal field parameter 10Dq.

3

Some Aspects of Solid State Radioluminescence

100%

Wojtowicz A.

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vol. 95

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issue 1

165-178

EN

In this paper we review results of radioluminescence studies on two scintillator materials, LuAlO_{3} and YAlO_{3}, activated with Ce. The experiments include measurements of ther moluminescence, isothermal phosphorescence decays, scintillation light yield as function of temperature, and scintillation time profiles under gamma excitation. Experimental results are interpreted in the frame of a simple kinetic model that includes a number of electron traps. We have identified and characterized a number of deep and shallow traps and demonstrated that traps in LuAlO_{3}:Ce are deeper than corresponding traps in YAlO_{3}:Ce. Unlike deep traps which are responsible for some scintillation light loss but otherwise do not have any impact on generation of scintillation light, shallow traps are shown to actively interfere with the process of radiative recombination via Ce ions. We demonstrate that shallow traps are responsible for some as yet unexplained observations including a higher room temperature light yield of YAlO_{3}:Ce and its longer scintillation decay time, as well as a longer scintillation rise time in LuAlO_{3}:Ce.

4

Charge Traps in Ce-Doped CaF_{2} and BaF_{2}

51%

Drozdowski W., Przegiętka K., Wojtowicz A., Oczkowski H.

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vol. 95

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issue 2

251-258

EN

Thermoluminescence of CaF_{2}:Ce, BaF_{2}, and BaF_{2}:Ce irradiated at room temperature is reported. X-ray induced emission spectra of the samples show that both excitonic (due to e^{-}+V_{K} recombination) and Ce^{3+} d-f luminescence may contribute to thermoluminescence signal. The simple Randall-Wilkins model is used to deconvolute glow curves into seven to eight first-order peaks. Parameters of all traps are calculated and correlations between peaks in the curves of the examined materials are discussed.

5

Thermoluminescence and Scintillation Time Profiles of BaF_{2}:Ce

51%

Głodo J., Szupryczyński P., Wojtowicz A.

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vol. 95

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issue 2

259-268

EN

In this communication we present results of measurements of low temperature thermoluminescence, isothermal decays, steady state radioluminescence yield, and scintillation time profiles at various temperatures on two scintillator materials, BaF_{2}:Ce and undoped BaF_{2}. We find that all these results can be consistently interpreted in the frame of a model that includes several relatively shallow charge traps. We have identified and characterized one particular shallow trap that causes the decay of the dominant scintillation component of BaF_{2}:Ce to be slower than radiative, as well as a set of others that are responsible for even slower components in the scintillation time profile of this material.

6

Luminescence and Scintillation Properties of Ce_{x}La_{1-x}F_{3} Monocrystals

51%

Wojtowicz A., Balcerzyk M., Lempicki A.

Acta Physica Polonica A

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1993

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vol. 84

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issue 5

963-968

EN

In this communication we present our results concerning luminescence and scintillation properties of mixed cerium-lanthanum trifluoride monocrystals, Ce_{x}La_{1-x}F_{3}. The luminescence, luminescence excitation spectra and decays are complex, indicating the presence of Ce^{3+} ions in regular and parasitic "perturbed" sites. The efficient energy transfer from regular Ce^{3+} ions (emitting at 286 and 303 nm) to "perturbed" Ce^{3+} ions (emitting at 340 nm) and the lack of the fast energy migration between Ce^{3+} ions are responsible for non-exponential decays of the short-wavelength emission and a relatively long rise-time of the long-wavelength emission. The short-wavelength emission decays are described by the Inokuti-Hirayama model of statistically distributed donors and acceptors. Our estimates of oscillator strengths, at 13.1 × 10^{-3} for Ce^{3+}, and 13.5 × 10^{-3} for Ce^{3+}_{per}, confirm that the d-f transition on the Ce^{3+} ion in a different site must be responsible for the long-wavelength emission. Calculations of the Ce-Ce and Ce-Ce_{per} energy transfer rates give 7.7 × 10^{5} s^{-1} and 1.56 × 10^{9} s^{-1}. The concentration of "perturbers" in good CeF_{3} samples has been reduced down to about 0.11%. It is likely that the constant and significant progress made by crystal growers (Optovac Inc.) may eventually produce a superior material for applications in high energy and nuclear physics.

7

Evolutionary algorithm for a reconstruction of NOE paths in NMR spectra of RNA chains

51%

Błażewicz J., Szachniuk M., Wojtowicz A.

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issue 3

8

Photoluminescence Kinetics of YAG Crystals Activated with Ce, and Ce and Mg

39%

Barzowska J., Kubicki A., Grinberg M., Kaczmarek S., Łuczyński Z., Wojtowicz A., Koepke C.

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vol. 95

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issue 3

395-402

EN

A basic spectroscopic measurements of luminescence, absorption, luminescence excitation spectra and emission kinetic measurements on YAG crystals activated with cerium and magnesium are presented. We report that the Ce^{3+} luminescence decay constant, at 65 ns, is independent of Ce concentrations (from 0.05 to 0.2%) and that it does not change with the presence or absence of the Mg co-dopant. Nevertheless, we find that under pulsed laser excitation at 290 nm the rise time in Ce luminescence time profiles is effectively shorter in the Mg co-doped samples.

9

Excited State Absorption and Thermoluminescence in Ce and Mg Doped Yttrium Aluminum Garnet

39%

Wiśniewski K., Koepke C., Wojtowicz A., Drozdowski W., Grinberg M., Kaczmarek S., Kisielewski J.

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vol. 95

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issue 3

403-412

EN

In this paper we report preliminary results of optical studies on Y_{3}Al_{5}O_{12} (YAG) crystals codoped with Ce and Mg. By using measurements of luminescence, absorption, and luminescence excitation spectra we demonstrate that although the basic features introduced to the YAG host by the Ce-doping remain intact, the Mg-codoping imposes some significant changes on other properties of the material. These changes are potentially important for laser and/or scintillator applications of YAG:Ce and are due, most likely, to modifications of defect populations in the material. We characterize them by using the techniques of thermoluminescence and excited state absorption under excimer laser pumping. These techniques, interestingly, yield results that seem inconsistent. While the thermoluminescence signal of the Mg-doped sample is strongly reduced, suggesting that trap concentrations in the presence of Mg are suppressed, the excited state absorption signal, which we also relate to the traps, is higher. We offer a tentative explanation of this contradiction between the two experiments that involves a massive transfer of electrons from the Mg-related defects to the excited state absorption centers caused by the excimer pump itself.

10

Spectroscopy and Thermoluminescence of LuAlO_{3}:Ce

33%

Wiśniewski D., Drozdowski W., Wojtowicz A., Lempicki A., Dorenbos P., de Haas J., van Eijk C., Bos A.

Acta Physica Polonica A

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1996

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vol. 90

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issue 2

377-384

EN

The present status of the LuAlO_{3}:Ce scintillator is reviewed. Scintillation mechanism of this material is based on capture by Ce^{3+} of holes and then electrons from their respective bands. Results of spectroscopic and thermoluminescence experiments are presented to support this model.

11

Thermal Desorption Studies of Ar^{+} Implanted Silicon

33%

Drozdziel A., Wojtowicz A., Turek M., Pyszniak K., Maczka D., Slowinski B., Yushkevich Y., Zuk J.

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vol. 125

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issue 6

1400-1404

EN

Thermal desorption spectrometry measurements were performed for Ar implanted Si samples. Implantation energy E_{i} varied in the range 85-175 keV. The release of implanted Ar in two steps was observed in the temperature range 930-1300 K: the relatively narrow peak at lower temperature ( ≈ 930 K for implantation fluence 5 × 10^{16} cm^{-2}) is due to the release of Ar from the agglomerations (bubbles) while the broader peak observed for higher temperatures ( ≈ 950 K for implantation fluence 5 × 10^{16} cm^{-2}) comes from Ar atoms diffusing out of the sample. Inverse order of peaks is observed compared to the results for lower energy implantations (< 50 keV). Analyzing the thermal desorption spectra collected for different heating ramp rates enabled estimation of the desorption activation energy (2 eV for E_{i} = 85 keV and 1.7 eV for E_{i} = 115 keV).

Refine search results

New High Performance Scintillators Based on Re-Activated Insulator Materials

Physics of Solid-State Laser Materials

Some Aspects of Solid State Radioluminescence

Charge Traps in Ce-Doped CaF_{2} and BaF_{2}

Thermoluminescence and Scintillation Time Profiles of BaF_{2}:Ce

Luminescence and Scintillation Properties of Ce_{x}La_{1-x}F_{3} Monocrystals

Evolutionary algorithm for a reconstruction of NOE paths in NMR spectra of RNA chains

Photoluminescence Kinetics of YAG Crystals Activated with Ce, and Ce and Mg

Excited State Absorption and Thermoluminescence in Ce and Mg Doped Yttrium Aluminum Garnet

Spectroscopy and Thermoluminescence of LuAlO_{3}:Ce

Thermal Desorption Studies of Ar^{+} Implanted Silicon