Linewidth of the infrared absorption spectra due to bound-to-continuum transition in GaAs/AlxGa1-xAs multiple quantum well structures

We have observed an extremely narrow absorption spectrum due to bound-to-continuum transition in GaAs/AlxGa1-xAs multiple quantum wells (MQWs). Its linewidth is only about one tenth of the values reported previously. Our calculation indicates that the broadening of the excited state in the continuum has little contribution to the absorption linewidth. We have grown a sample whose MQW region contains two kinds of wells with a minor thickness inhomogeneity. Its resultant absorption linewidth is six times as large as that of homogeneous well sample, which is in good agreement with our theoretical analysis. Thus we can suggest that the wider absorption spectra reported by many authors may be due to the well width inhomogeneity. (C) 1998 American Institute of Physics. [S0003-6951(98)03430-5]

ELECTRIC-FIELD-INDUCED EXCITON-LINEWIDTH BROADENING IN SHORT-PERIOD GAAS/GAXAL1-XAS SUPERLATTICES

We have investigated the Wannier-Stark effect in GaAs/GaAl1-xAs superlattices under electric fields by photocurrent spectroscopy measurements in the range of temperatures 10-300 K. The linewidth of the Oh Stark-ladder exciton was found to increase significantly along with an increase in peak intensity when the electric field increases. We present a mechanism based on an enhanced interface roughness scattering of electronic states due to Wannier-Stark localization in order to explain this increased broadening with electric field. This electric-field-related scattering mechanism will weaken the negative differential conductance effects in superlattices predicted by Esaki and Tsu.

BROADENING OF THE EXCITONIC LINEWIDTH DUE TO SCATTERING OF 2-DIMENSIONAL FREE-CARRIERS

By photoluminescence measurements we find that at low temperature the linewidth of the excitonic luminescence broadens with increasing electron density in the wider well from a photoexcited type-I-type-II mixed GaAs/AlAs asymmetric double quantum well structure, which even makes the excitonic linewidth at 77 K larger than at 300 K above a certain excitation intensity. We verify that the broadening is due to the scattering of two-dimensional carriers to excitonic states. Based on the theory of the scattering of carriers to excitonic states, we calculate the broadening of the excitonic linewidth. Our experimental results are convincing for verifying the theoretical prediction. (C) 1995 American Institute of Physics.

Photoluminescent properties of organic film in flat optical microcavity

The microcavity is sandwiched between a quarterwavelength distributed Bragg reflector(DBR) and a metal Ag reflective mirror. A single layer of a Tris(8-quinolinolato)aluminum (Alq) film was used as the light-emitting layer. The photoluminescent properties of the optical microcavity and that of the Alq film were studied at the same excitation condition. Compared with the Alq film,the significantly narrowed spectral emission linewidth from 90 nm to 10 nm was observed, the PL emission intensity of the microcavity at the resonant mode is enhanced by the order of 1. The spectral narrowing and intensity enhancement of the microcavity is attributed to the microcavity effect.

Exchange narrowing effects in the EPR linewidth of Gd diluted in Ce compounds

Anomalous thermal behavior on the EPR linewidths of Gd impurities diluted in Cc compounds has been observed. In metals, the local magnetic moment EPR linewidth, Delta H, is expected to increase linearly with the temperature. In contrast, in CexLa1-xOs2 the Gd EPR spectra show a nonlinear increase. In this work, the mechanisms that are responsible for the thermal behavior of the EPR lines in CexLa1-xOs2 are examined. We show that the exchange interaction between the local magnetic moments and the conduction electrons are responsible for the narrowing of the spectra at low temperatures. At high temperatures, the contribution to the linewidth of the exchange interaction between the local magnetic moments and the Ce ions has an exponential dependence on the excitation energy of the intermediate valent ions. A complete fitting of the EPR spectra for powdered samples is obtained, (C) 1998 American Institute of Physics. [S0021-8979(98)39911-9].

EPR linewidth of local magnetic moments diluted in Ce intermediate-valence compounds

Anomalous thermal behavior on the EPR linewidths has been observed for Gd impurities diluted in CexA1-xBn (A=La,Y, B=Ir,Os,Rh,Pd) intermediate-valence compounds. In this work we show that the exchange interaction between the local magnetic moments and the intermediate-valence host ions has an important contribution to the relaxation rates of the local moments. We calculated the relaxation, using the Redfield formalism and the ideas contained in the interconfigurational fluctuation model of Hirst. We show that the exchange interaction contribution has an exponential dependence on the excitation energy of the intermediate-valence ions. © 1992 The American Physical Society.