Search

Radio- and thermoluminescent properties of HfO 2 :Ti sintered ceramics were investigated in the temperature range of 10–300 K. Fabrication atmosphere altered somewhat the efficiency of radioluminescence but did not affect the spectral distribution of the broad scintillation band covering the 380–570 nm range of wavelengths and peaking at 522 nm at 10 K and about 490 nm at 300 K. The analogous shift was seen in photoluminescence. Scintillation efficiency was continuously growing from 10 K to 300 K, while photoluminescence intensity was stable in the 10–250 K range of temperatures and was reduced by about 30% at 300 K. Analysis of these observations allowed to conclude that diffusion of carriers generated upon the impact of high-energy photons towards the Ti emitting center is strongly temperature-dependent and inferior at lower temperatures. Upon exposure to X-rays at 10 K the ceramics stored more than 50% of the absorbed energy. This energy could be recovered later upon thermal stimulation of the ceramics. Four main thermoluminescent peaks were then produced at 95, 140, 243 and 278 K. This effect was tentatively associated with theoretically predicted self-trapping of holes in HfO 2 . The so-called partial cleaning and T max –T stop experiments indicated that some fraction of traps shows a continuous distribution of their depths. [ABSTRACT FROM AUTHOR]

Radioluminescence and UV-excited photoluminescence spectra, photoluminescence time profiles, thermoluminescence glow curves and gamma-excited energy spectra (determining scintillation light yields) of several Lu2SiO5:Ce and Y2SiO5:Ce samples were recorded. The results are analyzed with attention focused on possible correlations between trap distributions, VUV responses, and light yields. The aspect of two distinct sites occupied by Ce3+ ions is also discussed. [Copyright &y& Elsevier]

Open f-shell rare-earth (RE) ions in wide bandgap host materials are usually characterized by closely spaced electronic levels due to various electron configurations and charge states. These levels provide convenient luminescent transitions that can be excited by efficient recombination of charge carriers generated in the host material by ionizing radiation. Therefore, it is the area of ionizing radiation detectors, where search for new, fast and efficient scintillator materials for high-energy physics and nuclear medicine, has yielded much of the recent advances in the understanding of radioluminescence and scintillation mechanism in some solid state, UV and VUV luminescent, RE-activated materials. In this paper we shall present selected results of basic experiments such as radioluminescence, VUV spectroscopy, time profiles and thermoluminescence, on barium fluoride (activated with Ce, Pr, Nd, Tb) and two aluminum perovskites, YAlO3 and LuAlO3, activated with Ce. We shall demonstrate that these results point to consecutive carrier capture and recombination at RE ions as the basic mechanism of radioluminescence and scintillation in these materials, despite the strong self-trapping and poor charge transport properties. Consequently, various electron and/or hole traps that intercept and retain for some time the recombining charge carriers play an active role influencing both the scintillation light yield and time profiles of scintillation pulses in these and many other wide bandgap RE-activated luminescent materials. [Copyright &y& Elsevier]

Abstract β-Ga 2 O 3 and β-Ga 2 O 3 :Ce crystals have been grown by the Czochralski method and their scintillation properties have been studied by means of pulse height, radioluminescence and scintillation time profile measurements. It is shown that although the scintillation of β-Ga 2 O 3 :Ce is related to intrinsic excitonic emission, the doping with Ce improves some characteristics of the material. The prominent samples of β-Ga 2 O 3 :Ce display fast 6 ns (40%) scintillation, with total light yields of about 5000 ph/MeV. Highlights • β-Ga 2 O 3 and β-Ga 2 O 3 :Ce crystals have been grown by the Czochralski method. • Semiconducting samples (pure and Ce-doped) scintillate with yields of ∼5000 ph/MeV. • Doping with Ce improves some properties of β-Ga 2 O 3. [ABSTRACT FROM AUTHOR]

Lu 2 Y 2 Al 2 O 9 :Pr crystals have been grown by the micro-pulling-down method and their basic luminescence properties have been examined in order to estimate their utility for scintillator applications. The performed studies comprise the measurements of radioluminescence spectra as a function of temperature, photoluminescence emission and excitation spectra, and low temperature thermoluminescence glow curves. A comparison of the present results with those obtained recently for Y 4 Al 2 O 9 :Pr indicates that in spite of a higher density Lu 2 Y 2 Al 2 O 9 :Pr is a much less promising material, which is mainly due to the absence of the fast Pr 3+ d-f emission. [ABSTRACT FROM AUTHOR]

X-ray excited emission spectra at various temperatures, as well as low temperature glow curves of Czochralski-grown Li 2 B 4 O 7 :Co (LTB:Co) single crystals, have been recorded and compared with the data available for undoped LTB and LTB:Eu,Mn. Although the presence of cobalt does not influence the radioluminescence of the material, it clearly alters its thermoluminescence; specifically, the number of peaks in the glow curve of LTB:Co is reduced as against that of LTB and LTB:Eu,Mn. This observation and its possible interpretations shed new light on the issue of shallow traps in lithium tetraborate crystals. [ABSTRACT FROM AUTHOR]

β-Ga 2 O 3 is an emerging ultra-wide bandgap (4.9 eV) oxide semiconductor that additionally scintillates under gamma excitation. A unique combination of transparency in the UV/visible spectrum, semiconducting, and scintillation properties makes that compound interesting for fundamental studies of underlying physics and design of novel devices, in particular compact detectors for gamma radiation. Undoped, and singly (Ce, Si, Al), doubly (Ce + Si, Ce + Al), and triply (Ce + Al + Si) doped bulk β-Ga 2 O 3 single crystals were grown by the Czochralski method under very similar conditions and systematically studied in terms of electrical and optical properties that were correlated with scintillation light yield under gamma excitation. A wide spectrum of doping enabled to control the free electron concentration in semiconducting β-Ga 2 O 3 crystals within almost three orders of magnitude (7 × 1015–6 × 1018 cm−3) with the Hall mobility approaching 150 cm2 V−1s−1. The maximum of light yield under gamma excitation was recorded for undoped and Ce-doped β-Ga 2 O 3 single crystals having the free electron concentration of mid 1016 cm−3. The light yield significantly decreases for both electrically insulating and highly conducting (Si-doped) crystals. None of the dopants (Ce, Si, Al) introduces any absorption bands in the spectral region of light emission (340–410 nm) under gamma excitation. The dopants in quest do not affect the structure of neither cathodoluminescence (CL) nor radioluminescence (RL) emissions, but modify their absolute intensity. A double-band structure of RL spectra corresponds to UV and blue emissions observed in CL spectra that are assigned to self-trapped excitons. Image 1 • Doped semiconducting β-Ga 2 O 3 was grown and studied for gamma radiation detection. • The crystals are fully transparent to scintillation emissions at 340–410 nm. • Maximum of light yield was found at free electron concentration of mid 1016 cm−3. • Luminescence spectra point to self-trapped excitons in scintillation mechanism. [ABSTRACT FROM AUTHOR]