Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Final Activity Report Summary - GLOSS-EE (Glossy magazine quality colour e-paper)

The first project task was related to growth and assembly of nanoparticles for possible applications in displays. Quantum dots are potentially very useful materials for efficient displays and light sources because their optical properties can be tuned relatively easily during the manufacturing process. A protocol for synthesising InP quantum dots was developed. As being currently prepared InP quantum are barely luminescent owing to many surface defects. Hence coating with a shell material having a higher band gap was needed. Using a ZnS shell, luminescent quantum dots were made and characterised. Visual changes observed in the photoluminescence spectra of InP/ZnS quantum dots in the temperature range of 300 to 510 K were studied closely. As this effect might be of potential relevance in applications as indicator of the temperature of a surface, we investigated the origin of this colour change by performing temperature dependent photoluminescence studies. A procedure for conjugating commercial available InGaP nanocrystals with biomolecules was also developed. Fabrication of a silicon photodiode was achieved and of a protocol for performing a biological assay using the photodiode and quantum dots has been developed.

The second project component was related to high and low refractive index materials with tuned optical properties to reduce light losses in displays and light emitting diode (LED) light sources. In achieving high efficiency displays and LED light sources it was crucial to use optical coupling and adhesive layers with the right index of refraction, adhesion and photo-thermal stability. Sol-gel formulations and processing techniques were developed for materials with a tuneable index of refraction. For low-index materials nano-porous materials and processing were developed with controlled pore size, surface and pore content. For high-index bonding layers, zirconium oxide nano-particles were used. Alternatively, a process using Ti acetylacetonate or Ti alkoxide was developed. The light scattering properties of the layers was tuned with a TiO2-SiO2 sol-gel material system where a controlled volume scattering and surface roughness could be achieved. Micro-structured high-index sol-gel coatings were demonstrated using embossing.

The third project task was concerned with the realisation of new concept backlight displays using diffractive optics and photonic materials. Actual liquid crystal display systems presented a very low efficiency, of about 5 %, in the light management. Several optical layers absorbed most of the light produced by the lamps of the device and only a small portion of that arrived to the eyes of the user. A new idea was developed to improve the actual situation. If a diffraction grating was integrated in the lightguide that distributed the light all over the display, the main three colours, i.e. red, green and blue, of the source could be separated by the grating and addressed by a system of micro-lenses to the right pixels of the display. This could help avoid the use of light-wasting colour filters in front of the pixel matrix. Surface relief diffraction structures were designed and realised by holography in photo-resist material. The diffraction gratings were optically characterised and compared to the theoretical predictions. A proof of principle prototype backlight system consisting of a lightguide with a suitable diffraction grating and a micro-lens array was realised and characterised. An improved configuration was demonstrated, showing a highly efficient pattern of red-green-blue-green-red coloured pixels.

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