This review discusses how low-energy, valence excitations created by swift electrons can render information on the optical response of structured materials with unmatched spatial resolution. Electron microscopes are capable of focusing electron beams on sub-nanometer spots and probing the target response either by analyzing electron energy losses or by detecting emitted radiation. Theoretical frameworks suited to calculate the probability of energy loss and light emission (cathodoluminescence) are revisited and compared with experimental results. More precisely, a quantum-mechanical description of the interaction between the electrons and the sample is discussed, followed by a powerful classical dielectric approach that can be in practice applied to more complex systems. We assess the conditions under which classical and quantum-mechanical formulations are equivalent. The excitation of collective modes such as plasmons is studied in bulk materials, planar surfaces, and nanoparticles. Light emission induced by the electrons is shown to constitute an excellent probe of plasmons, combining sub-nanometer resolution in the position of the electron beam with nanometer resolution in the emitted wavelength. Both electron energy-loss and cathodoluminescence spectroscopies performed in a scanning mode of operation yield snap shots of plasmon modes in nanostructures with fine spatial detail as compared to other existing imaging techniques, thus providing an ideal tool for nanophotonics studies.

/pdf/optical-excitations-in-electron-microscopy-3d2rfnfkst.pdf

Optical excitations in electron microscopy

In this review, the major achievements and research and development (R&D) trends from the last decade in the field of single crystal scintillator materials are described. Two material families are included, namely, those of halide and oxide compounds. In most cases, the host crystals are doped with Ce3+, Pr3+ or Eu2+ rare earth ions. Their spin- and parity-allowed 5d–4f transitions enable a rapid scintillation response, on the order of tens to hundreds of nanoseconds. Technological recipes, extended characterization by means of optical and magnetic spectroscopies, and theoretical studies are described. The latter provide further support to experimental results and provide a better understanding of the host electronic band structure, energy levels of specific defects, and the emission centers themselves. Applications in medical imaging and dosimetry, security measures, high-energy physics and the high-tech industry, in which X(γ)-rays or particle beams are used and monitored, are recognized as the main driving factor for R&D activities in this field.

Recent R&D Trends in Inorganic Single-Crystal Scintillator Materials for Radiation Detection

The primary goal of this review is to present a clear chemical perspective of borates in order to stimulate and facilitate the discovery of new borate-based optical materials. These materials, whic...

Borates: A Rich Source for Optical Materials.

Y3Al5O12(YAG):Ce3+ is the most widely applied phosphor in white LEDs (w-LEDs) because of strong blue absorption and efficient yellow luminescence combined with a high stability and thermal quenching temperature, required for the extreme operating conditions in high-power w-LEDs. The high luminescence quenching temperature (∼600 K) has been well established, but surprisingly, the mechanism for temperature quenching has not been elucidated yet. In this report we investigate the possibility of thermal ionization as a cause of this quenching process by measuring thermoluminescence (TL) excitation spectra at various temperatures. In the TL excitation (TLE) spectrum at room temperature there is no Ce3+:5d1 band (the lowest excited 5d level). However, in the TLE spectrum at 573 K, which corresponds to the onset temperature of luminescence quenching, a TLE band due to the Ce3+:5d1 excitation was observed at around 450 nm. On the basis of our observations we conclude that the luminescence quenching of YAG:Ce3+ at ...

/pdf/insight-into-the-thermal-quenching-mechanism-for-y3al5o12-xom1er6ef1.pdf

Insight into the Thermal Quenching Mechanism for Y3Al5O12:Ce3+ through Thermoluminescence Excitation Spectroscopy

Current technologies for X-ray detection rely on scintillation from expensive inorganic crystals grown at high-temperature, which so far has hindered the development of large-area scintillator arrays. Thanks to the presence of heavy atoms, solution-grown hybrid lead halide perovskite single crystals exhibit short X-ray absorption length and excellent detection efficiency. Here we compare X-ray scintillator characteristics of three-dimensional (3D) MAPbI3 and MAPbBr3 and two-dimensional (2D) (EDBE)PbCl4 hybrid perovskite crystals. X-ray excited thermoluminescence measurements indicate the absence of deep traps and a very small density of shallow trap states, which lessens after-glow effects. All perovskite single crystals exhibit high X-ray excited luminescence yields of >120,000 photons/MeV at low temperature. Although thermal quenching is significant at room temperature, the large exciton binding energy of 2D (EDBE)PbCl4 significantly reduces thermal effects compared to 3D perovskites, and moderate light yield of 9,000 photons/MeV can be achieved even at room temperature. This highlights the potential of 2D metal halide perovskites for large-area and low-cost scintillator devices for medical, security and scientific applications.

/pdf/x-ray-scintillation-in-lead-halide-perovskite-crystals-xsraolm2tk.pdf

X-ray Scintillation in Lead Halide Perovskite Crystals

Scintillation properties of selected oxide monocrystals activated with Ce and Pr

The self-organized rodlike microstructure of terbium-scandium-aluminum garnet−terbium-scandium perovskite, Tb3Sc2Al3O12−TbScO3, eutectic crystals has been studied. The growth of the eutectic by the...

Self-organized, rodlike, micrometer-scale microstructure of Tb3Sc2Al3O12-TbScO3:Pr eutectic

(LuxY1-x)3Al5O12:Pr (x = 0.25, 0.50, 0.75) crystals have been grown by the Czochralski method and their scintillation properties have been examined. Compared to the well-respected LuAG:Pr scintillator, which has so extensively been studied in the recent years, the new mixed LuYAG:Pr crystals display markedly higher light yields, regardless of the value of x. In particular, (Lu0.75Y0.25)3Al5O12:0.2%Pr characterized by a yield of 33000 ph/MeV, an energy resolution of 4.4% (at 662 keV), and a density of 6.2 g/cm3, seems to be an ideal candidate to supercede Lu3Al5O12:0.2%Pr (19000 ph/MeV, 4.6%, 6.7 g/cm3) in various applications. The observed enhancement of light output following the partial substitution of lutetium by yttrium is most probably related to some specific differences in distributions of shallow traps in particular materials.

/pdf/33000-photons-per-mev-from-mixed-lu0-75y0-25-3al5o12-pr-ca3degbcuq.pdf

33000 photons per MeV from mixed (Lu0.75Y0.25)3Al5O12:Pr scintillator crystals

Cerium and molybdenum-activated lutetium aluminum perovskite (LuAlO3, LuAP) and mixed lutetium-yttrium aluminum perovskite (LuxY1−xAlO3, LuYAP) scintillator crystals have been grown by the Czochralski method at the Institute of Electronic Materials Technology (ITME, Warsaw). In this paper we report the measurements of scintillation light yields, absorption spectra, scintillation time profiles, low temperature thermoluminescence, and room temperature afterglow, performed on polished 2×2×10 mm3 pixel samples cut from larger boules. We show that scintillation properties of the LuAP:Ce and LuAP:Ce,Mo crystals from ITME place them among the best crystals produced commercially.

J. Kisielewski

Papers

Scintillation properties of selected oxide monocrystals activated with Ce and Pr

Self-organized, rodlike, micrometer-scale microstructure of Tb3Sc2Al3O12-TbScO3:Pr eutectic

33000 photons per MeV from mixed (Lu0.75Y0.25)3Al5O12:Pr scintillator crystals

Scintillation properties of LuAP and LuYAP crystals activated with Cerium and Molybdenum

Thermoluminescence and scintillation of praseodymium-activated Y3Al5O12 and LuAlO3 crystals