119HIGHLIGHTS 2020

This experiment, which can be extended by adding lasers to control the number of trapped electrons, solves the longstanding question concerning the chemical nature of the traps. It turns out that only a few percent of the dysprosium ions participate

Fig. 103: HERFD-XANES spectra for the (a) Eu and (b) Dy LIII edges upon violet (coloured line) or IR (black line) irradiation (top), compared to conventional XANES of reference spectra (middle) and their difference spectra (bottom). c) Time evolution of the lanthanide oxidation states,

relative to the total [Eu]+[Dy] content from HERFD-XANES. Simultaneously, the luminescence is probed for (d) the Eu2+ and (e) the Dy3+ emission. The X-ray beam is switched on at time t = 0.

in the trapping process, so there is room for improvement in energy storage capacity. Brighter glow-in-the-dark compounds enable more demanding applications, following an improved understanding of the delicate interactions in these fascinating materials.

Identification of Dy3+/Dy2+ as Electron Trap in Persistent Phosphors, J.J. Joos (a), K. Korthout (a,b), L. Amidani (c,d), P. Glatzel (c), D. Poelman (a,b) and P. Smet (a,b), Phys. Rev. Lett. 125,

033001 (2020); https://doi.org/10.1103/ PhysRevLett.125.033001. (a) LumiLab, Department of Solid State Sciences, Ghent University, Gent (Belgium) (b) Center for Nano- and Biophotonics

(NB Photonics), Ghent University, Gent (Belgium) (c) ESRF (d) Current address: Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany)

PRINCIPAL PUBLICATION AND AUTHORS

LARGE POLARON QUASIPARTICLES IN SrTiO3 AND SrTiO3 -BASED 2D ELECTRON GAS

Quasiparticles in metals and semiconductors are formed through the interactions of electrons (holes) with the elementary excitations of the solid, like phonons and magnons. High-energy-resolution resonant inelastic X-ray scattering (RIXS) was used to find the spectroscopic signature of large polarons in one of the most studied and simple perovskite materials, SrTiO3 (STO), and related two-dimensional electron gas (2DEG).

Large polarons are quasiparticles composed of electrons (holes) and long-range polar distortion of the lattice, which move as free quasiparticles with an effective mass larger than the free electron value. The possibility that large polarons may form in STO studies, as a result of the coupling of electrons to high-energy LO3 optical phonon mode, have been proposed by optical spectroscopy [1,2] and angle-resolved photoemission studies [3]. However, their role in the transport properties of STO and STO-based 2DEGs remains unclear.

To this purpose, a thorough study of the elementary low-energy excitations of STO and

STO-based 2DEGs was carried out using high- energy-resolution RIXS at beamline ID32, with a resolution three times better than previous studies on other titanates and on the LAO/STO system. Figures 104a-c show typical Ti L3-edge X-ray absorption spectroscopy and RIXS data acquired at 20 K on conducting and insulating bulk STO samples in the low energy-loss range with incoming photon energies at the A3 (2p3/2 to 3dt2g excitation) and B1 (2p3/2 to 3deg excitation) peaks, and B0, 1.6 eV above A3, which is a resonance for the excitation of 2p3/2 core electrons into 3d1 states. It is possible to identify in the spectra (Figure 104d) low- (25-30 meV, w1), middle- (55-65 meV, w2), and high-energy