In recent years, energy transfer ͑ET͒ using semiconductor quantum dots ͑QDs͒ is getting increased attention. However, it has been postulated that ET between QDs is based on the Förster model, which is a wellestablished model of ET mechanism in organic dye systems, without verification. In this work, we have investigated ET mechanism in colloidal CdS QDs measuring photoluminescence dynamics of a bilayer structure consisting of differently sized CdS QDs. In the bilayer structure, the distance between the monolayer of donor QDs and that of acceptor QDs was controlled precisely by a spacer layer that is layer-by-layer assembly of polyelectrolytes. The bilayer structure enabled us to systematically measure the spacer-layer dependence of photoluminescence dynamics reflecting the ET process between QDs. It is demonstrated that ET between the donor and acceptor QDs is conclusively dominated by the dipole-dipole interaction, which verifies the appropriateness of the Förster model.Since the first report of quantum size effects in semiconductor doped glasses 1 and also in colloidal solutions 2 in the early 1980s, semiconductor quantum dots ͑QDs͒ have attracted considerable attention. So far, many studies have been conducted from a scientific viewpoint to understand the intrinsic nature of physical/chemical properties of QDs, as well as from interest in the application to new functional materials. 3-6 A turning point in QD studies was the development of monodispersed colloidal QDs having high photoluminescence ͑PL͒ yield with use of rapid injection of organometallic precursors into hot coordinating solvents ͑hot-injection method͒. 7,8 The breakthrough in synthesizing the new class of colloidal QDs have led to an explosive increase in QD studies and opened up possibilities for various applications such as biomolecular imaging, 9 QD lasing, 6,10 and QD solar cells. 11,12 Randomly dispersed QDs have been a major target in most of the studies so far. The dynamical process of resonant ET between CdSe QDs was reported in recent years. 13,14 This opened up a new aspect in photophysics of semiconductor QDs and stimulated studies on QD-based energy transfer ͑ET͒ processes employing QDs as energy donors in QDbioconjugate systems 9 and QD-organic dye systems, 15,16 as well as ET between QDs. 17,18 All of the studies, however, have postulated that ET employing QDs is based on the Förster model 19 that is a typical ET mechanism between organic molecules. It should be noted that the appropriateness of the Förster model for explanation of ET in QDs has not been verified until now. For the experimental clarification of the ET mechanism, it is essential to measure PL dynamics in a well-designed sample structure in which the distance between QDs was precisely controlled.How can we control the distance between QDs? We have focused on a layer-by-layer ͑LBL͒ assembly. 20-22 LBL is a simple and powerful technique allowing the realization of a multilayer structure that is controlled at a molecular level. This technique is based on the sequential a...

In the published version of our paper, the expression for k ET is incorrect ͑the left hand column of page 4͒. This equation should bewhere PVA and bilayer are the decay time of the bright exciton state in the PVA film sample and that in the bilayer structure, respectively.It is noted that they are just typographical errors and that the calculations in the paper are based on the correct equation.

The ternary layered Tl-contained semiconductor ferroelectrics TlInS2, TlGaS2, and TlGaSe2, exhibiting an incommensurate phase and a relaxor state with temperature, were approached down to 0.76eV at room temperature by spectroscopic phase modulated ellipsometry in a region below the energy gap of each material. By using both coherent and incoherent reflection modes on only the layer-plane surfaces, the refractive indices in the parallel- and perpendicular-to-the-layers directions of the light propagation were determined. Sellmeier single-oscillator form was used to fit the model data to the experimental intensities. The discrepancy between the model and experimental data was shown to be negligible. Besides, a self-consistent picture of the obtained refraction indices was emerging after the discussion based on the available data for the studied materials. The applied experimental approach was thus found to be quite effective for layered materials, and the obtained refractive indices might be used for database with high degree of confidence.

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The temperature dependence of the absorption edge of the layered TlInS2 was studied in a region of the incommensurate phase by spectroscopic phase modulated ellipsometry (SPME) on (001) surfaces in incoherent reflection mode that was sensitive to both E⊥C* and E//C* components of the reflected light (C*: the direction bisecting the angle between two optic axes). The energy position of the absorption edge, which was obtained from the measured Ic signal, was found to exhibit an irregular behavior with temperature in a similar way with the obtained earlier temperature dependence of excitons. It is proposed that this behaviour reflects the changes in electronic spectrum due to the temperature phase transition while the peaking anomaly of the measured in‐layer‐plane optical anisotropy is mostly related with the spatial structure of the incommensurate phase. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)