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.

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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 ...

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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.

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X-ray Scintillation in Lead Halide Perovskite Crystals

Magnetic multilayers of (Ir/Co/Pt)6 with interfacial Dzyaloshinskii-Moriya interaction (IDMI) were deposited by magnetron sputtering with Co thickness d=1.8 nm. Exploiting magneto-optical Kerr effect in longitudinal mode microscopy, magnetic force microscopy, and vibrating sample magnetometry, the magnetic field-driven evolution of domain structures and magnetization hysteresis loops have been studied. The existence of weak stripe domains structure was deduced – tens micrometers size domains with in-plane “core” magnetization modulated by hundred of nanometers domains with out-of-plane magnetization. Micromagnetic simulations interpreted such magnetization distribution. Quantitative evaluation of IDMI was carried out using Brillouin light scattering (BLS) spectroscopy as the difference between Stokes and anti-Stokes peak frequencies Δ f. Due to the additive nature of IDMI, the asymmetric combination of Ir and Pt covers led to large values of effective IDMI energy density Deff. It was found that Stokes and anti-Stokes frequencies as well as Δ f, measured as a function of in-plane applied magnetic field, show hysteresis. These results are explained under the consideration of the influence of IDMI on the dynamics of the in-plane magnetized “core” with weak stripe domains.

https://aip.scitation.org/doi/pdf/10.1063/9.0000339

Magnetization statics and dynamics in (Ir/Co/Pt)6 multilayers with Dzyaloshinskii–Moriya interaction

Rare-earth doped SrLaGa3O7 single crystal are promising laser materials. Also crystal doped with Ho3+ ions could be used as efficient laser in visible and near IR regions. Laser materials, generating in visible and IR regions, can be used for optical data recording in micro photolithography and in medicine. SrLaGa3O7 single crystal doped with 0.3, 1.5 and 2 at percent of Ho3+, respectively were grown by the Czochralski method with use of iridium crucible and after heater. According to EPMA measurements distribution coefficient of Ho3+ in SrLaGa3O7 was estimated to be k approximately equals 0.22. Optical absorption spectra in visible and IR regions were measured at 300K and 12K respectively. Optical quality of single crystals was checked by the use of computerized imaging spectropolarimeter and polariscopic measurements. Temperature dependence of capacitance and conductivity for different dopant concentrations were also measured.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Czochralski growth and characterization of SrLaGa 3 O 7 :Ho 3+ single crystals

Er3+ and Yb3+ Doped Active Media for “Eye Safe” Laser Systems.

http://przyrbwn.icm.edu.pl/APP/PDF/90/a090z2p24.pdf

UV and Gamma Irradiation Effect in Spectroscopic and Lasing Properties of Er3+doped Yttrium-Aluminium Garnet, Yttrium Orthoaluminate and Lithium Niobate Crystals

Changes in optical properties of some oxide compounds (YAG, YAG:Nd 3+ , YAG:Ce 3+ , YAG:Ce 3+ ,Mg 2+ , YAG:Cr 3+ , YAG:Cr 4+ , SrLaGa3O7:Dy 3+ , SrLaGa3O7:Cr 3+ , SrGdGa3O7:Cr 3+ , LiNbO3:Cr 3+ and LiNbO3:Cu 2+ ) induced by 21 MeV proton irradiation were studied. In the optical absorption spectra lines which belong to optically active dopants (like Ce 3+ , Cr 3+ , Fe 3+ ) and F-type color centers are seen. Influence of proton irradiation on such centers is observed. It seems to be attributed to the ionization and/or recombination of definite centers. Moreover, for relatively high proton fluencies, Frenkel defects are probably created.

J. Kisielewski

Papers

Magnetization statics and dynamics in (Ir/Co/Pt)6 multilayers with Dzyaloshinskii–Moriya interaction

Czochralski growth and characterization of SrLaGa 3 O 7 :Ho 3+ single crystals

Er3+ and Yb3+ Doped Active Media for “Eye Safe” Laser Systems.

UV and Gamma Irradiation Effect in Spectroscopic and Lasing Properties of Er3+doped Yttrium-Aluminium Garnet, Yttrium Orthoaluminate and Lithium Niobate Crystals

Interaction of protons with oxide compounds