(a) Cross-sectional confocal microscopy image of the graded LBL film of CdTe NPs made of 10 bilayers of "green", yellow", "orange", and "red" NPs (total 40). Small NPs are assembled in the lower part (green and yellow luminescence), while bigger NPs are assembled on top of them (orange and red luminescence). The total thickness of the film was estimated to be 220±20 nm by the same technique. (b) Schematic arrangement of the conduction and valence energy levels of the film in (a).
Exciton Recycling in Graded Gap Nanocrystal Structures
Frster resonant energy transfer (FRET)
cascaded energy transfer (CET) Nano Lett., 2004, 4, 1599-1603
Diagram of the excitonic energy levels in the REF (a) and the CET (b) sample. The thick lines represent the bottom of the exciton band, thin solid lines the vibronic progressions. The dotted lines symbolize trap states. (a) Most of the excitons in the REF sample are trapped in surface states, from where they decay nonradiatively. Only defect-poor NCs contribute significantly to the PL yield. Even defect-poor NCs may be affected via exciton transfer to defect-rich NCs. (b) Excitons in the six layers of smaller sized NCs are trapped in surface states similar to the trapping in the REF sample. However, the trapped excitons can be transferred very efficiently from layers with smaller NCs to layers with larger NCs. Most importantly, these recycled excitons finally reach the center layer of red-emitting NCs with only low excess energy which reduces the probability of being trapped.
Nanostructured artificial nacre
(i) The material of seashell nacre and bones are well known for their hardness, strength and toughness—superior to many man-made ceramics and composites—complemented by unique biological/biomedical properties. Their distinctive mechanical qualities are attributed to a highly regular brickand-mortar arrangement of organic and inorganic elements, which combines the elasticity of 10–50 nm protein layers (for example β-chitin and lustrins) and the strength of CaCO3 tablets 200–900 nm thick. (ii) The structure–function harmony of nacre and other hard biological tissues has inspired a large class of biomimetic advanced materials and organic/inorganic composites. The addition of inorganic components, such as clays, to organic polymers noticeably improves the mechanical, barrier and thermal properties of polymers and Rubbers.

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