The photoluminescence from a variety of individual molecules and nanometre-sized crystallites is defined by large intensity fluctuations, known as 'blinking', whereby their photoluminescence turns 'on' and 'off' intermittently, even under continuous photoexcitation. For semiconductor nanocrystals, it was originally proposed that these 'off' periods corresponded to a nanocrystal with an extra charge. A charged nanocrystal could have its photoluminescence temporarily quenched owing to the high efficiency of non-radiative (for example, Auger) recombination processes between the extra charge and a subsequently excited electron-hole pair; photoluminescence would resume only after the nanocrystal becomes neutralized again. Despite over a decade of research, completely non-blinking nanocrystals have not been synthesized and an understanding of the blinking phenomenon remains elusive. Here we report ternary core/shell CdZnSe/ZnSe semiconductor nanocrystals that individually exhibit continuous, non-blinking photoluminescence. Unexpectedly, these nanocrystals strongly photoluminesce despite being charged, as indicated by a multi-peaked photoluminescence spectral shape and short lifetime. To model the unusual photoluminescence properties of the CdZnSe/ZnSe nanocrystals, we softened the abrupt confinement potential of a typical core/shell nanocrystal, suggesting that the structure is a radially graded alloy of CdZnSe into ZnSe. As photoluminescence blinking severely limits the usefulness of nanocrystals in applications requiring a continuous output of single photons, these non-blinking nanocrystals may enable substantial advances in fields ranging from single-molecule biological labelling to low-threshold lasers.

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In October 1999, Eastman Kodak and Sanyo Electric jointly announced the development of a high quality, 2.4 inch diagonal Full Color active matrix Organic Light Emitting Diode (OLED) display. This technology demonstration resulted from the successful integration of Kodak's organic electroluminescence display technology and Sanyo's low temperature polysilicon TFT technology. Commercial samples are expected to reach the market in 2001. The active matrix OLED displays feature a wider viewing angle and a faster response speed than conventional LCDs. With its low power consumption, high brightness and thin design, these OLED displays when incorporated in digital cameras, personal digital assistants (PDA), videophones and other portable imaging devices, will offer a superior value proposition to consumer electronics products. Several OLED display designs are under development now to serve various market segments. This paper will summarize the status of active matrix full color OLED display development, the key technical challenges, and the path ahead.

We present an exact classical solution to the problem of dipole emission in a planar multilayer light-emitting device. The inputs to the model are the photoluminescence and quantum yield of the emitter material, and the device layer thicknesses and indices of refraction. The results of the model are applied to predicting the radiant intensity of organic light-emitting diodes as a function of varying device layer thickness. It is shown that the predicted radiances are in excellent agreement with the data. We also present results for the Poynting power distribution from a randomly aligned dipole for positions both internal and external to the diodes.