LONDON Researchers at Sony Deutschland GmbH (Stuttgart, Germany) and the Max-Planck–Institute for Polymer Research, (Mainz, Germany) have demonstrated the possibility of bendable optically assessed organic light emitting displays for the first time, based on red or IR-A light upconversion.
They claim in a paper published Thursday (Oct. 2) in the New Journal of Physics titled "Annihilation Assisted Upconversion: All Organic, Flexible and Transparent Multicolour Displays" that the technology has significant advantages when compared to the traditional methods used for projection displays and televisions.
The researchers note that, with LCD-based projection displays, the liquid crystal acts as a filter for the light being shone through so when coherent excitation is used (e.g. laser diodes) the problems with speckles are serious. For this organic emissive UC displays, the organic molecules themselves emit non-coherent light in 4 directions to produce an image.
Sony announced the development of flexible OLED display screens in 2006 but glitches such as size and resolution limitations, and the difficulty of structuring the organic compounds so as not to be distorted when bent, have stopped designs coming to market.
The scientists suggest that the optically excited organic emissive displays do not suffer from this problem and give further opportunities for new applications.
They add that through the use of a new structure and novel combinations for the organic compounds within viscous polymeric matrix, there need be no size or resolution limitations for the new screens. The display size, they say, would be limited mainly by the size of the optical substrates, although tiling would be fairly straightforward.
"To the best of our knowledge we demonstrate for the first time a versatile colour all-organic and transparent UC-display. The reported displays are also flexible and have excellent brightness," say the researchers.
Applications include computers that can be folded up and put pockets, the mass-production of moving image posters for display advertising, televisions which can be bended to view or, better screens for the emerging e-readers sector.
The devices work with ultra-low excitation intensities down to 20mWcm-2 red or near-IR light.
The displays are based on metallated-porphyrin sensitizers in combination with emitters dispersed in a transparent polymeric matrix and are driven by galvoscanned laser diodes. The displays are said to have external quantum yield as high as 3.2 percent.
The response time can be adjusted to specific application requirements—up to 80µs allowing kHz-refreshment rate of the displayed information. The researchers claim it is possible to easily tune the optical density of the screens in order to obtain a desired transmittance for the excitation beam.
The prototype displays are said to have stable operation for 100 hours.
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