We study terahertz (THz) radiation transmission through grating-gate graphene-based nanostructures. We report on room-temperature THz radiation amplification stimulated by current-driven plasmon ...excitation. Specifically, with an increase of the dc current under periodic charge density modulation, we observe a strong redshift of the resonant THz plasmon absorption, followed by a window of complete transparency to incoming radiation and subsequent amplification and blueshift of the resonant plasmon frequency. Our results are, to the best of our knowledge, the first experimental observation of energy transfer from dc current to plasmons leading to THz amplification. Additionally, we present a simple model offering a phenomenological description of the observed THz amplification. This model shows that in the presence of a dc current the radiation-induced correction to dissipation is sensitive to the phase shift between oscillations of carrier density and drift velocity. And, with an increasing current, the dissipation becomes negative, leading to amplification. The experimental results of this work, as all obtained at room-temperature, pave the way toward the new 2D plasmon-based, voltage-tunable THz radiation amplifiers.
Short interrupted repeat cassette (SIRC)-a novel DNA element found throughout the
nuclear genome. SIRCs are represented by short direct repeats interrupted by diverse DNA sequences. The maxima of ...SIRC's distribution are located within pericentromeric regions. We suggest that originally SIRC was a special case of the complex internal structure of the miniature inverted repeat transposable element (MITE), and further MITE amplification, transposition, and loss of terminal inverted repeats gave rise to SIRC as an independent DNA element. SIRC sites were significantly enriched with several histone modifications associated with constitutive heterochromatin and mobile genetic elements. The majority of DNA-binding proteins, strongly associated with SIRC, are related to histone modifications for transcription repression. A part of SIRC was found to overlap highly inducible protein-coding genes, suggesting a possible regulatory role for these elements, yet their definitive functions need further investigation.
We provide a detailed introduction to a method we recently proposed for calculating the spectrum of excitations of effective strings such as QCD flux tubes. The method relies on the approximate ...integrability of the low-energy effective theory describing the flux tube excitations and is based on the thermodynamic Bethe ansatz. The approximate integrability is a consequence of the Lorentz symmetry of QCD. For excited states, the convergence of the thermodynamic Bethe ansatz technique is significantly better than that of the traditional perturbative approach. We apply the new technique to the lattice spectra for fundamental flux tubes in gluodynamics in
D
= 3 + 1 and
D
= 2 + 1, and to
k
-strings in gluodynamics in
D
= 2 + 1. We identify a massive pseudoscalar resonance on the worldsheet of the confining strings in
SU
(3) gluodynamics in
D
= 3 + 1, and massive scalar resonances on the worldsheet of
k
= 2.3 strings in
SU
(6) gluodynamics in
D
= 2 + 1.
Alpha and gamma spectroscopy (pulse height spectra and scintillation decay time profiles) were used to study scintillating properties of composite scintillators systems consisting of single ...crystalline films (SCF) and single crystal (SC) substrate plates. α-particles of 241Am of energy 5.4857 MeV and γ-quanta of 137Cs of energy 661.66 keV are used as excitation sources of SCFs or SC substrates, respectively. As SC substrates mainly LuAG:Pr single crystal plates are used and these plates are characterized by light yield (LY) between 10-21 × 103 ph/MeV, Energy Resolution (ER) ~5% at 661.66 keV and good proportionality. LuAG:Ce, Lu2-xGdTbxAG:Ce and Lu3-xTbxAG:Ce SCFs at x = 0.15–2.285 were prepared by LPE method onto LuAG:Pr substrates and investigated. LY of LuAG:Ce SCF under α-particles excitation is about of 60% than that of LuAG:Pr SC substrate. The LY of Lu3-x TbxAG:Ce SCFs depend nonlinearly on Tb3+ concentration in the 0.15–2.285 range and changed from 60-62% to 106–109%, respectively, in comparison with LY of LuAG:Pr SC substrate. Detailed scintillation decay time profiles have shown that there are differences between the decay curves of composite scintillators under α-particles and γ-quanta excitations. Such differences are characterized using the tα/tγ ratio between the time of scintillation decay to 1/e, 0.1, 0,05 and 0.02 levels under α-particles excitation (tα) and γ-quanta excitation (tγ). From all studied types of composite scintillators, based on the LuAG:Pr substrates, the highest value of tα/tγ ratio can be reached for Lu3-xTbxAG:Ce SCF/LuAG:Pr SC substrate composite scintillators at Tb content x = 2.15–2.275, where this ratio is equal to 4.2–6.2 at scintillation decay level of 0.1.
•Pulsed height spectra under α- and γ-rays were used to study scintillating properties.•α-particles of 241Am allow to excite only single crystalline films as LuAG:Ce and LuAG:Ce,Tb.•Ratio of tα/tγ scintillation decay intensities should be the highest for new prepared Lu3-xTbxAG:Ce garnets.•Composite scintillators can to resolve various of parts ionizing radiation components as α-particles, ions or γ-quanta.
► Growth processes of Lu2SiO5:Ce and Y2SO5:Ce single crystalline films onto Y2SO5:Ce substrates by liquid phase epitaxy method. ► Comparison of the luminescence properties of Lu2SiO5:Ce and Y2SO5:Ce ...crystals and films. ► Influence of lead flux related impurity on the properties of Lu2SiO5:Ce and Y2SO5:Ce films.
Single crystalline films (SCFs) of undoped and Ce3+ doped Y2SiO5 (YSO) and Lu2SiO5 (LSO) orthosilicates were crystallized for the first time by liquid phase epitaxy method onto undoped YSO substrates from melt-solution based on PbO–B2O3 flux. The scintillation and luminescent properties of YSO:Ce and LSO:Ce SCFs were compared with the properties of bulk single crystal counterparts. We show that the peculiarities of luminescent properties of YSO:Ce and LSO:Ce SCFs in comparison with the crystal analogues are caused by the different distribution of Ce3+ ions over Y1/Lu1 and Y2/Lu2 positions of YSO and LSO host and strong influence of Pb2+ flux-related impurity on luminescent properties of Ce3+ ions.
This work is devoted to the development of two novel types of advanced composite scintillators based on single crystalline films (SCFs) of Lu
3
Al
5
O
12
garnet (LuAG), doped with Ce
3+
and Pr
3+
...ions, and substrates from single crystals (SCs) of Sc
3+
doped LuAG using the liquid phase epitaxy (LPE) method. We show the possibility for simultaneous registration of α-particles and γ-quanta using separation of the decay kinetics of the SCF and crystal parts of such composite scintillators. Namely, large differences in the respective scintillation decay kinetics and decay time values
t
α
and
t
γ
are observed for LuAG:Ce SCF/LuAG:Sc SC and LuAG:Pr SCF/LuAG:Sc SC composite scintillators under excitation by α-particles from an
241
Am (5.5 MeV) source and γ-quanta from a
137
Cs (662 keV) source. Thus, both developed types of composite scintillators can be applied for simultaneous registration of α-particles and γ-quanta in mixed radiation fluxes. The rate of discrimination of the scintillation signals, coming from the SCF and SC parts of the LuAG:Ce SCF/LuAG:Sc SC composite scintillator, expressed by the
t
γ
/
t
α
ratio, is equal to 1.34-1.96 in the 0-1100 ns time interval. For the LuAG:Pr SCF/LuAG:Sc SC composite scintillators, more significant differences in the scintillation decay kinetics are achieved. In this case, the
t
γ
/
t
α
ratio for these composite scintillators reaches the values 9.6-15.6 in the wide 0-2500 ns time interval. This is the best result among all the types of composite scintillators we developed based on epitaxial structures of garnet compounds.
Top - Scheme of the composite scintillator for registration of α-particles and γ-quanta. Bottom - Samples of the LuAG:Ce SCF/LuAG:Sc SC (a) and LuAG:Pr SCF/LuAG:Sc SC (b) composite scintillators prepared using the liquid phase epitaxy growth method.
The paper is dedicated to the comparative study of the luminescent properties of LuAG:Ce films, grown by pulse laser deposition (PLD) and liquid phase epitaxy (LPE) methods, using the time-resolved ...luminescent spectroscopy under excitation by synchrotron radiation in the fundamental absorption range and above the band gap of LuAG host. We have shown the similarities and differences in the luminescence properties of LuAG:Ce PLD and LPE grown films. Specifically, the luminescence of LuAl antisite defects is absent in the emission spectra of both films in the room temperature range. Meanwhile, the low intensive bands peaked at 350 and 400 nm, corresponding to the luminescence of excitons localized around and bound with F+ centers, respectively, are present in the emission spectra of LuAG:Ce PLD films at 12 K. The energy of formation of the excitons bound with the Ce3+ ions, being equal to 7.52 eV at 12 K, and the energy of the onset of interband transitions of LuAG host, being equal to 7.76 eV (at 300 K), have been found for LuAG:Ce LPE and PLD films, respectively. We have also found that the scintillation properties of LuAG:Ce PDL film are worse in comparison with LPE grown film analogue due to the significantly larger content of the slow emission component in the scintillation decay under high-energy excitation. Such differences between the optical and scintillation properties of PLD and LPE films are caused by the different conditions of their preparation (in vacuum and in air).
•LuAG:Ce films were grown by PLD and LPE methods.•Luminescent properties of LuAG:Ce PLD and LPE films were compared using synchrotron radiation.•Peculiarity of luminescence LuAG:Ce PLD film were determined with respect to the properties of LPE grown film.
The study is dedicated to the development of scintillating screens for microimaging applications based on the single crystalline films (SCFs) of Eu
3+
-doped (Y,Lu,Gd,Tb)AlO
3
-mixed perovskites ...grown onto YAlO
3
substrates using the liquid phase epitaxy (LPE) method with the objective to optimize their X-ray stopping power and light yield. We confirm that the Eu
3+
-doped YAlO
3
and TbAlO
3
SCFs and full set of Lu
1−
x
Gd
x
AlO
3
SCFs with
x
values in the
x
= 0-1.0 range can be crystallized on YAlO
3
substrates using the LPE technique. The structural quality of films was studied using X-ray diffraction. The optical properties of Lu
1−
x
Gd
x
AlO
3
:Eu (
x
= 0-1) SCFs and TbAlO
3
:Eu mixed perovskites were also studied in this work in comparison with YAlO
3
:Eu SCF counterpart using the absorption, cathodoluminescence, photoluminescence (PL) emission and excitation spectra and PL decay kinetics as well as light yield measurements under e-beam and α-particles excitation. The Gd
3+
→ Eu
3+
and Tb
3+
→ Eu
3+
energy transfer processes are observed in Lu
1−
x
Gd
x
AlO
3
and TbAlO
3
:Eu SCFs, respectively, increasing the efficiency of the Eu
3+
luminescence in the perovskite hosts. Meanwhile, the highest light yield of the cathodoluminescence (CL) and radioluminescence (RL) under excitation by α-particles is found only in YAlO
3
:Eu, Lu
0.5
Gd
0.5
AlO
3
:Eu and GdAlO
3
:Eu SCFs. The light yield of CL and RL of these SCFs is notably higher than that in TbAlO
3
:Eu and LuAlO
3
:Eu SCFs and they even slightly (9-11%) overcome the light yield of the conventional Gd
3
Ga
5
O
12
:Eu SCF screens that are used in the microimaging detectors.
The study is dedicated to the development of scintillating screens for microimaging applications based on the single crystalline films of Eu
3+
-doped (Y,Lu,Gd,Tb)AlO
3
-mixed perovskites using the liquid phase epitaxy method.
In this study, the structural, luminescence and photoconversion properties of novel composite color converters based on Tb1.5Gd1.5Al5O12:Ce (TGAG:Ce) single crystalline films, grown by the liquid ...phase epitaxy method onto Y3Al5O12:Ce (YAG:Ce) single crystal substrates, are investigated. The luminescence and chromaticity properties for the set of TGAG:Ce SCF/YAG:Ce composite color converters, including color coordinates, color rendering index (CRI), and luminous efficacy, were studied by varying the thickness of the TGAG:Ce film in the 12–48 μm range and the Ce3+ concentration in the 0.1–0.5% range in YAG:Ce substrates. Such combination of different YAG:Ce substrates with various TGAG:Ce films enables tuning the white light tones from cold white (correlated color temperature (CCT) > 6000 K) to neutral white (6000 K > CCT > 3300 K). The theoretical white light color coordinates on the chromaticity diagram were almost achieved for TGAG:Ce film/YAG:Ce (0.5 mm) crystal converters with a film thickness between 19 and 25 μm under 465 nm LED excitation, with the corresponding CRI values in the 79–74 range. The developed composite color converters allow the problem of a high color temperature and low color rendering index of conventional WLEDs based on conventional YAG:Ce phosphor converters to be solved.
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