Czochralski-grown β-Ga2O3 and β-Ga2O3:Si crystals with the free electron concentrations between 2.5·1016 and 4.3·1018 cm−3 have been characterized by means of pulse height and scintillation time ...profile measurements in order to assess their basic scintillation properties. At room temperature, with increasing free electron concentration in the studied range, the scintillation yields decrease from 8920 to 1930 ph/MeV, while the mean scintillation decay times pare down from 989 to 61 ns. However, when the brightest β-Ga2O3 sample is cooled down below 100 K, its scintillation yield exceeds 20000 ph/MeV.
•Czochralski-grown β-Ga2O3 and β-Ga2O3:Si crystals have been characterized.•Scintillation yield and decay times strongly depend on free electron concentration.•Scintillation yield clearly goes up with decreasing temperature towards liquid N2.
Measurements of light yield, low temperature thermoluminescence, and scintillation time profiles, performed comparatively on “as grown” and thermally annealed LuAG:Pr samples, are reported. It is ...shown that traps play an efficient role in the scintillation of LuAG:Pr, being responsible for the yield decrease and introducing a long component to the time profiles. The trap concentrations in the annealed crystals are lower than in the non-annealed ones, which correlates with the yield enhancement.
► Charge traps are responsible for scintillation yield decrease in LuAG:Pr. ► Trap concentrations can be reduced by thermal annealing, resulting in higher yield. ► 0.15 eV traps manifest themselves as long components in scintillation time profiles.
Low temperature thermoluminescence of β-Ga2O3, β-Ga2O3:Al and β-Ga2O3:Ce has been investigated. Glow curves have been analyzed quantitatively using a rate equations model in order to determine the ...traps parameters, such as activation energies, capture cross-sections and probabilities of recombination and retrapping.
•Undoped and doped β-Ga2O3 crystals have been grown by the Czochralski method.•Their glow curves between 10 and 350 K have been investigated.•Rate equations model has been used to determine traps parameters.
In this paper we present and discuss results of detailed spectroscopy studies of Pr3+ luminescence from the (Ba,La)F2:0.2 m%Pr crystals under UV and VUV synchrotron excitation.
We have measured time ...resolved emissions from the minor site Pr3+ in (Ba,La)F2:Pr at 10 and 300 K. The spectra clearly show the 1S0 emission from the Pr3+ ions in some low symmetry Pr-sites (we designate them La-sites) previously identified in higher concentration (0.3 m%Pr and more) crystals. However most of emission from the Pr activated (Ba,La)F2 crystals originates in Pr3+ ions in other sites which produce an efficient d-f emission. As demonstrated by excitation spectra, the emission from some of these sites (denoted as Ba-sites) closely resembles the d-f emission from BaF2.
The La-site, time resolved and long delay emission spectra are dominated by hypersensitive transitions from the 1S0 and 3P0 levels to lower energy levels of the 4f2 configurations. Only these transitions contribute to the photon cascade emission desired for some mercury free phosphor applications.
► Pr f-f and f-d time resolved emission spectra were measured. ► Emission from the minor La-site of Pr3+ in (Ba,La)F2:Pr was identified. ► Configuration coordinate diagrams of the Pr3+ in different sites were proposed.
In this paper we will present VUV spectroscopy experiments performed at the Superlumi station of Hasylab, DESY, Hamburg, on samples of BaF
2 crystals activated with Ce and BaF
2, (Ba,La)F
2 crystals ...activated with Er. The results of these experiments include time resolved luminescence and luminescence excitation spectra obtained under wavelength selective VUV and UV excitation by pulsed synchrotron radiation.
We will reveal the information provided by the VUV/UV excitation spectra of the Ce
3+ 5d
→
4f as well as Er
3+ 4f
n
−15d
→
4f
n
and 4f
n
→
4f
n
emissions on energy transfer mechanisms from the fluoride host to the rare earth ion. We will demonstrate that the fast energy transfer channels involve bound excitons while the generation of free electrons and holes leads to slower processes dependant on hole and/or electron trapping.
We will demonstrate that differences between the excitation spectra of the 5d
→
4f emission in Ce and 4f
105d
→
4f
11 emission in Er activated BaF
2 are generated by the coupling of the 4f
→
5d transition to the 4f
10 core of the Er
3+ ion. We will also identify the additional band, absent for Ce, which is due to the exchange split high spin (HS) state of the 4f
105d configuration responsible for the slow decay of the excited Er
3+ ions in BaF
2 and (Ba,La)F
2.
Finally we will provide evidence and explain why the dominant VUV 4f
105d
→
4f
11 Er
3+ emission in BaF
2 is spin-forbidden and slow while in the mixed (Ba,La)F
2 crystals it is spin-allowed and fast.
Rare-earth-activated wide bandgap materials for scintillators Wojtowicz, Andrzej J
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2002, Letnik:
486, Številka:
1
Journal Article
Recenzirano
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, YAlO
3 and LuAlO
3, 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.
X-ray excited emission spectra at various temperatures, as well as low temperature glow curves of Czochralski-grown Li2B4O7: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.
•Radioluminescence spectra of LTB:Co have been measured at various temperatures.•Glow curves of LTB:Co have been recorded between 10 and 300 K.•Trap parameters related to particular glow peaks have been derived.•Doping with cobalt has been found to deactivate some of the traps.
Lu2Y2Al2O9: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 Y4Al2O9:Pr indicates that in spite of a higher density Lu2Y2Al2O9:Pr is a much less promising material, which is mainly due to the absence of the fast Pr3+d-f emission.
•LuYAM:Pr crystals have been grown by the μPD method.•Radio-, photo-, and thermoluminescence of LuYAM:Pr have been studied.•At RT fast d-f luminescence of Pr3+ ions has not been detected.
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