The processes of intrinsic and extrinsic luminescence excitation by synchrotron radiation of 4–40 eV or electron pulses have been studied in $\alpha -{\mathrm{Al}}_2{\mathrm{O}}_3$ single crystals at 8 K. The intrinsic A (7.6 eV) and E emissions (3.77 eV) can be effectively excited in the region of long-wavelength (8.85–9.1 eV) and short-wavelength (9.1–9.3 eV) components of exciton absorption doublet, respectively. Fast (∼6 and ∼20 ns) and slow (∼150 ns) components of the A emission correspond to the creation of singlet and triplet $p^{5}s$ excitons. The efficiency of the A emission in the region of band-to-band transitions is low. The intensity of A emission sharply increases (approximately quadratically) with a rise of the excitation density by nanosecond electron pulses. In ${\mathrm{Al}}_2{\mathrm{O}}_3:\mathrm{S}\mathrm{c},$ the 5.6-eV luminescence is caused by the decay of near-impurity electronic excitations (∼8.5 eV) as well as by the electron recombination with holes localized near ${\mathrm{Sc}}^{3+}$ centers. The efficiency of 7.6-, 5.6-, and 3.8-eV emission sharply increases at the energy of exciting photons of $h\nu >25\mathrm{}\mathrm{eV}.$ One photon of 26–29 and 30–37 eV causes the ionization of the ${2p}^6$ or ${2s}^2$ shell of the oxygen ion and provides the creation of two or three electron-hole pairs, respectively. Long-term investigations of $\alpha -{\mathrm{Al}}_2{\mathrm{O}}_3$ crystals did not lead to the detection of immobile self-trapped holes or electrons. The A emission excited at the direct photocreation of excitons or at the recombination of free electrons and free holes is interpreted by us as the radiative decay of self-shrunk excitons. The theoretical model of Sumi allows the existence of such immobile self-shrunk excitons even if an electron and a hole do not separately undergo the self-trapping.

The technological challenge imposed by the time resolution essential to achieve real-time molecular imaging calls for a new generation of ultrafast detectors. In this contribution, we demonstrate that CdSe-based semiconductor nanoplatelets can be combined with standard scintillator technology to achieve 80 ps coincidence time resolution on a hybrid functional pixel. This result contrasts with the fact that the overall detector light output is considerably affected by the loss of index-light-guiding. Here, we exploit the principle of 511 keV energy sharing between a high-Z, high stopping power bulk scintillator, and a nano-scintillator with sub-1 ns radiative recombination times, aiming at a breakthrough in the combined energy and time resolution performance. This proof-of-concept test opens the way to the design and study of larger size sensors using thin nanocomposite layers able to perform as efficient time taggers in a sampling detector geometry of new generation.

Synchrotron-radiation excited ion mass spectrometry has been used to study the 3s3${\mathit{p}}^6$np(n≥4) resonances in argon at 25.0–29.3 eV. It is shown using a time-independent resonant scattering approach that the Fano parametrization may be applied to overlapping resonances. For the Dubau-Seaton profile an exact expression of the closed-channel phase shift is obtained. We find that regarding the window character of the Ar 3s series the Fano parameters calculated using the multichannel multiconfiguration Dirac-Fock method are in good agreement with those derived from fitting a convoluted Fano function to the measured n=4 autoionizing resonance. The Fano parameters are also derived from perfect fits to the 5≤n≤8 resonances which tests the validity of this parametrization to overlapping members of an inner-valence electron resonance series. In contrast, a parametrization of the entire series based upon the Dubau-Seaton formula did not result in a good fit without modifications. Using the same value of the shape parameter we find, however, that the n=4 resonance can be accurately represented by both the Fano and Dubau-Seaton profiles.