記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We have observed the lasing of submicron-sized ZnO particle in a Fabry-Perot cavity at low temperatures. A thin alkali-halide crystal including a small amount of ZnO particles are sandwiched between two quartz plates arranged as a pair of opposite mirrors, that is, a Fabry-Perot cavity. Under low excitation due to a He-Cd laser, emissions of free and bound excitons and their phonon replicas are recognized markedly, while a biexciton emission band appears under high-dense excitation by a pulsed N(2) laser. Biexciton lasing is demonstrated as a narrowed emission by focusing the excitation light beam on an appropriate position being a ZnO particle in the cavity. When a cavity length satisfies the resonant condition, the lasing occurs in the spectral region of the biexciton emission band and with the very small divergence angle. The obtained threshold of excitation-power density is about 0.50 MW/cm(2). We discuss lasing in terms of stimulated emission caused by population inversion between biexciton and exciton states. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.2128690

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Time-resolved luminescence spectra have been measured in NaGdF4:Eu3+ in order to investigate quantum cutting in which two visible photons are emitted for one-photon absorption. In a Gd3+-Eu3+ system, two processes of energy transfer from Gd3+ to Eu3+ are dominant in the quantum cutting: a cross-relaxation (CR) process and a direct-transfer (DT) process. In temporal profiles of the luminescence spectra, it was found that. one visible emission undergoing the CR process indicates a fast decay, and the other undergoing the DT process indicates a rising form. These results are explained by two energy-transfer processes contributing to the quantum cutting process. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2004.01.011

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Time-resolved spectra of luminescence from the lowest excited state of Gd3+ ((6)p(7/2)) have been studied in various Gd compositions in NaY1-xGdxF4 (0.1 less than or equal to x less than or equal to 1). Two emission bands are observed at room temperature: 311 nm band corresponding to an intrinsic state on Gd sublattice, and 313 nm band corresponding to a trap state on irregular Gd sites. In NaGdF4, a temporal profile of the 311 nm band shows an apparent rise at about 100 mus and a long decay time of about 10 ms, while that of the 313 nm band shows a simple exponential decay with about 3 mus. When Gd concentration is diluted with Y3+, the rise part of the 311 nm band decreases and the decay time of the 313 nm band becomes long, though the rise time of the 311 nm band does not change. At low temperature, the 311 nm band disappears and the decay time of the 313 nm band is much prolonged in NaGdF4. These results are discussed in terms of the energy transfer from the trap state to the intrinsic Gd state in the Gd sublattice. The trap state plays an important role in the dynamics of the energy relaxation. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-2313(02)00633-6

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Time-resolved luminescence spectra have been investigated in NaGdF4. NaY0.90Gd0.10F4 and NaGdF4:Eu3+ under ArF excimer laser (193 nm) excitation. In NaGdF4, the well-known emission lines in Gd3+ at 311 nm (P-6(7/2) --> S-8(7/2)) and 305 nm (P-6(5/2) --> S-8(7/2)) start to grow at I ts after the laser pulse and take maximum intensity at 300 mus. It is found that emissions at 313 and 307 nm decayed with a fast decay time of 3 mus. In NaY0.90Gd0.10F4, temporal changes of the emission bands are quite different from those of NaGdF4. In NaGdF4 : Eu3+, the decay time of the 311 nm emission in Gd3+ is shorter than that in NaGdF4, and some new emission lines appear at 100 mus after pulse irradiation. The energy transfer through Gd 3- sublattice is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-2313(01)00292-7

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

Thin crystalline solid films of KBr1-xIx:Tl+ were prepared from a melt by a cell method and impurity absorption spectra were investigated at 11 K for the whole composition range. In the middle composition range no spectral traces of phase separation were observed, indicating that the films were in a state equivalent to that of a supersaturated solid solution. The A band of KBr:Tl+ and that of KI:Tl+ were persistent with each other and two additional bands attributable to the A bands of the mixed crystals were apparent in the range of 0.01 less than or equal to x less than or equal to 0.5. According to the results of Gaussian fitting of the bands, it was evident that two of them have threshold compositions with increasing I- ion composition x. In addition, the I- ion concentration around the impurities was found to be greater than the I- ion composition of the host materials. These findings are discussed in terms of a model, according to which the bands are associated with various I- ion configurations around the impurities. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0040-6090(00)01893-9

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WORLD SCIENTIFIC PUBL CO PTE LTD  

We investigated the absorption spectra of KI under excitation by an ArF excimer laser at 11 K. The laser light excited the sample through a one-photon process. Stable F centers were formed with excitation at a power level above similar to 2 mJ/cm(2). From the time-resolved absorption spectrum, it is evident that the F centers are generated within 50 ns after the time of initiation of the laser pulse. The width of the F band at 50 ns was broader than that of the stationary F band at 11 K, suggesting the temperature increase of the crystal. We discuss the relaxation process in KI under dense electronic excitation.

DOI： 10.1142/S021797920100869X

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Laser ablation and color center formation of KBr crystals have been investigated under irradiation of an ArF excimer laser. A threshold fluence of the macroscopic surface fracture of bulk KBr crystals has been determined to be 23 mJ/cm(2). It is found that highly dense F and F-aggregate centers are induced near the surface by using very thin KBr crystals; their surfaces are protected by quartz plates. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-2313(99)00303-8

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Sample specimens of ZnO particles embedded in thin alkali halide crystals (KI, KBr and KCl) have been prepared from their melts and photoluminescence spectra have been measured at low temperature. In cases of Ki and KBr matrices, a bound exciton and a free exciton emission line appear clearly, and in KCl matrix, the emission lines are very sharp in comparison with the other cases. The sharpest lines in KCl matrix are only obtained during the time of a few minutes. The particles are kept in the melt above the melting temperature. These facts suggest that the use of the alkali halide melt and rapid solidification of the melt result in a proper etching of the particle surface. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-2313(99)00422-6

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN J APPLIED PHYSICS  

We have prepared samples of ZnO particles embedded in thin alkali halide crystals by a melt growth method and have measured photoluminescence spectra at various temperatures. In the spectra measured at 8.5 K, free exciton (FE) and bound exciton (BE) emission lines are clearly recognized, while the well-known green band is hardly observed. The FE line appears at temperatures between 8.5 K and 300 K. The widths of both lines are very sharp and almost equal to that of ZnO epitaxial layers grown by a molecular beam epitaxy method. These results strongly suggest that high-quality ZnO particles can be well embedded in thin alkali halide crystals.

DOI： 10.1143/JJAP.38.L1318

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN J APPLIED PHYSICS  

We have prepared samples of ZnO particles embedded in thin alkali halide crystals by a melt growth method and have measured photoluminescence spectra at various temperatures. In the spectra measured at 8.5 K, free exciton (FE) and bound exciton (BE) emission lines are clearly recognized, while the well-known green band is hardly observed. The FE line appears at temperatures between 8.5 K and 300 K. The widths of both lines are very sharp and almost equal to that of ZnO epitaxial layers grown by a molecular beam epitaxy method. These results strongly suggest that high-quality ZnO particles can be well embedded in thin alkali halide crystals.

DOI： 10.1143/jjap.38.L1318

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：GORDON BREACH SCI PUBL LTD  

Radiation effects of an ArF excimer laser (193 nm) have been studied for two kinds of samples of alkali iodides. One is the usual bulk crystals and the other the thin crystals grown in a small gap of two quartz plates. After irradiation, we have found a remarkable striped pattern in both samples by a microscope. The pattern is well interpreted in terms of the light intensity distribution of the Fresnel diffraction induced by a knife edge. The microscopic mechanism of the appearance of the pattern is discussed on the basis of the Raman scattering spectra of both samples.

DOI： 10.1080/10420159908226231

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.58.13835

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We study spatial behavior of heavily excited excitons localized at a two-dimensional space of a specific stacking fault interface in a layered crystal (Formula presented) Pump-and-probe absorption and resonant luminescence spectra of the exciton states were measured with an intense nanosecond laser not only at the exciting laser spot but at distant points from the exciting spot by applying space-resolved spectroscopy methods. The blueshift proportional to the exciton density was clearly observed on the probe absorption spectra even at the distant points due to high-density excitons flowing out from the exciting spot. The resonant luminescence also shows the spectral change and anomalous spatial expansion depending on the excitation density. The spatial distributions of the energy shift on the probe absorption and the luminescence intensity were analyzed on the basis of a two-dimensional exciton-flow model with dissipation processes. The analysis suggests the existence of an efficient in-phase motion of the exciton polaritons at high density. The results are discussed in terms of a new phase of the interacting high-density exciton-polariton system. ? 1998 The American Physical Society.

DOI： 10.1103/PhysRevB.58.13835

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

Macroscopic and efficient spreading of excitons from an exciting laser spot to the outside area along a quasi two-dimensional space of a planar-defect in BiI3 is presented by space- and time-resolved photoluminescence, and the degenerate Four Wave-Mixing (DFWM) signals by use of spatially separated two laser-beams. The photoluminescence shows wide spreading due to polariton-like transfer of excitons at low density and wider that at higher density. The fast transfer of excitons at high density was detected as a coherent exciton-flow by the DFWM measurements.

DOI： 10.1016/0960-8974(96)83620-5

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Macroscopic exciton transport phenomena from a small area of an exciting laser spot to outside the spot along a quasi-two-dimensional planar defect in BiI3, are presented from space-resolved pump-probe absorption, photoluminescence, and four-wave-mixing measurements. At high intensity, the blue shift of tile transition energy at the point away from the pump spot is analyzed by the 2-D diffusion. The four-wave-mixing signals are detected with time delays when the two laser beams are spatially separated.

DOI： 10.1016/0022-2313(95)00188-3

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

We have studied high density effects and their spatial distribution on the absorption spectra of excitons localized at a specific planar-defect structure in layered BiI3 crystals in which a quasi two-dimensional space with the translational symmetry is realized and the center-of-mass motion of excitons is confined. The exciton transition energy was examined by a space-resolved pump-probe method. The blue-shift of the transition energy has been detected not only at the exciting laser spot but also at the different site away from the exciting point. This is the first observation of high density effects on the exciton spectra at the isolated area from the source due to the spatial propagation of excitons.

DOI： 10.1016/0038-1098(95)00029-1

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The high density effects of excitons excited at a two-dimensional stacking-fault plane in layered BiI3 crystal is investigated. The blue-shift and broadening have been observed for the high density excitation. A new transition appears below the resonance exciton energies, which is attributed to the two-photon transition to a bi-exciton state.

DOI： 10.1016/0022-2313(94)90243-7

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：EDITIONS PHYSIQUE  

Saturation spectra of the excitons confined and localized at several kinds of stacking disorders in layered crystal BiI3 are studied. The quasi-two dimensional exciton localized at the stacking fault interface does not saturate its absorption strength below the density of 10(5)W/cm2 due to the large binding energy and the lateral center-of-mass motion along the interface. On the exciton system associated with some polytypic structures contained in a very small region, an obvious absorption saturation is observed. The behaviour of absorption saturation is well described by a saturation effect on a simplified two-level system having a homogeneous line broadening. An absorption saturation is also observed on the confined excitons in mesoscopic domains induced by the external deformation of the crystal. The pumping-laser photon-energy dependence of the saturation density characterizes this exciton system to be inhomogeneous.

DOI： 10.1051/jp4:1993593

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Absorption line series W J (J=I,II,III,…) appeared below the indirect edge in BiI 3 has been studied. The series is assigned to the excitons confined in mesoscopic domains produced by deformation faults characteristic of layered materials. Each line consists of four structures which correspond to x+iy, x−iy, z, and pure triplet states originated from the bulk cationic excitons. The energy separations between these four states are depend on the size of mesoscopic domains in which an exciton is confined. By introducing a disk-like shape model of the mesoscopic domain, the experimental results are analyzed on the basis of anisotropic quantum size effects on the cationic excitons. The relative motion of the exciton is found to be strongly affected by the localization of the translational motion in the direction perpendicular to the confinement axis. ? 1992, Taylor & Francis Group, LLC. All rights reserved.

DOI： 10.1080/10587259208047012

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Highly resolved excitation spectra for the self-trapped exciton luminescence (sigma, pi, and E(x) bands) and for the 1s free exciton luminescence under the two-photon absorption have been studied in RbI at 2 K. These spectra are composed of broad peaks with fine structures: the broad peaks are attributed to the 2p-, 3p- and 4p-exciton transitions, and the fine structures to the energy splitting of the 2p-exciton state by the envelope-hole coupling. The shapes of these excitation spectra are explained by the process of the two-photon absorption with the simultaneous creation of an LO phonon and by the energy relaxation of the p excitons. The former process is treated with third order perturbation theory.

DOI： 10.1016/0022-2313(92)90051-A

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：TAYLOR & FRANCIS LTD  

DOI： 10.1080/10587259208047012

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