Mamoru Kitaura

Luminescence due to dimer type self-trapped excitons in lead halides

Abstract Recombination luminescence in lead halides (PbCl 2 and PbBr 2 ) has been investigated by the VUV light excitation above the band gap energy. An intense blue-green (BG) emission band is observed at 2.62 eV both in PbCl 2 and in PbBr 2 . The same BG emission is also observed under illumination by the red light from a HeNe laser on the crystals pre-irradiated with X-ray. The temperature dependence of the BG emission intensity shows rather complicated behavior. As raising temperature, a prominent hump appears around 85 K, which is attributed to thermo-luminescence resulting from recombination of thermally activated holes with STEL centers. The intensity of the BG emission decreases at temperatures above 140 K, corresponding to thermal instability of self-trapped electron (STEL) centers. Time dependence of the luminescence after pulsed light excitation comprises two stages, namely, rather quick decay in the μs region and long afterglow up to several tens ms. Two channels are proposed for the BG emission; one is the direct recombination process between the STEL and the hole center, the other radiative annihilation of the STE of the [(Pb 2 ) 3+ -STEL+hole] type.

Design and performance of a new VIS–VUV photoluminescence beamline at UVSOR-III

A new bending-magnet beamline with a 2.5 m normal-incidence monochromator mainly dedicated to photoluminescence measurements of solids has been constructed at the UVSOR-III.

Nonradiative branching processes of self-trapped excitons in cadmium halide crystals

Temperature dependence of luminescence spectra, intensity and life-time has been measured precisely in CdBr2 to investigate whole decay kinetics of self-trapped excitons (STEs). Below 50 K, a near-ultraviolet (UV) emission band appears at 3.3 eV. The initial state for the UV-emission consists of spin singlet and triplet states. The ratio of population branching of the optically created excitons into singlet to triplet was observed as 6:94. The triplet state further split into closely lying three levels. From analysis on the decay components, the ratio among initial populations of these levels was determined as 1:6:0 in order from lower to higher levels. Above 50 K, the intensity of the UV-emission decreases rather rapidly. About half of the STEs in the UV-state are transferred into another STE state responsible for yellow (Y) emission at 2.2 eV. Another half of STEs decay directly into ground state non-radiatively. The Y-state comprise two kinds of states, each of which further split into two states. Two pairs of decay components, namely four components, were observed between 50 and 150 K. Temperature dependence of time-integrated intensity was determined for each decay component. Above 150 K, all STEs are to be de-excited non-radiatively through thermal processes.

Topological phase transitions driven by magnetic phase transitions in Fe(x)Bi2Te3 (0≤x≤0.1) single crystals.

We propose a phase diagram for Fe(x)Bi2Te3 (0≤x≤0.1) single crystals, which belong to a class of magnetically bulk-doped topological insulators. The evolution of magnetic correlations from ferromagnetic to antiferromagnetic gives rise to topological phase transitions, where the paramagnetic topological insulator of Bi2Te3 turns into a band insulator with ferromagnetic-cluster glassy behavior around x∼0.025, and it further evolves to a topological insulator with valence-bond glassy behavior, which spans over the region from x∼0.03 up to x∼0.1. This phase diagram is verified by measuring magnetization, magnetotransport, and angle-resolved photoemission spectra with theoretical discussions.

Photoluminescence of orthorhombic and cubic single crystals

The photoluminescence of orthorhombic and cubic crystals has been studied with the use of a deuterium lamp or synchrotron radiation as the light source. The spectra of orthorhombic samples exhibit a single band at 2.07 eV, while the spectra of cubic samples show an intense band at 4.10 eV, accompanied by some other bands depending on the sample. These two main bands are stimulated only under exciton-band excitation. No luminescence is detected when both crystals are excited with photons in the band-to-band region. The present results are compared with earlier data for and which have the orthorhombic structure. The relaxation processes of excitons and electron-hole pairs in lead halides are discussed.

Sondheimer oscillation as a signature of surface Dirac fermions

Topological states of matter challenge the paradigm of symmetry breaking, characterized by gapless boundary modes and protected by the topological property of the ground state. Recently, angle-resolved photoemission spectroscopy (ARPES) has revealed that semiconductors of Bi

Determination of optical gain of self-trapped exciton luminescence in CdI2

_{2}

Time-resolved photoluminescence spectroscopy of Ce:Gd3Al2Ga3O12 crystals

Se

Energy location of Ce3+ 4f level and majority carrier type in Gd3Al2Ga3O12:Ce crystals studied by surface photovoltage spectroscopy

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Electronic Structure and Auger-Free Luminescence in Cs2ZnCl4 Crystals

and Bi