Nanomaterials as White Light Emitters for Low Cost Lighting

White-light emission (WLE) from semiconductor nanostructures is presently a research area of intense interest especially where the primary objective is to replace conventional light sources by environmentally friendly materials in order to minimize energy costs and therefore the global energy consumption for lighting. Presently the general methods to achieve white-light emission are either by coating a yellow phosphor or by combining green and red phosphors on a background consisting of a blue light emitting diode (LED) or by employing nanocrystals (NCs) of the three primary colours (red, green, blue) using multilayer structures in LEDs. However, when one simply mixes these nanocrystal quantum dots (QDs) of different colours together to generate white light, the efficiencies are often observed to decrease due to the re-absorption of light and subsequent undesired energy transfer (ET) leading to undesirable changes in the chromaticity coordinates and photometric performance due to the different relative temporal stabilities of the components.

Hence the use of a single-emitting component offers many advantages over multiple component systems for white light-emitting sources such as LEDs, amongst which are: greater reproducibility, low cost preparation, ease of modification and simpler fabrication processes. Therefore, it is of great importance to find high-quality single source white light emitters via low cost chemical synthesis approaches that will allow the production of white light while meeting the needs of industry, such as satisfactory Commission International d’Eclairage (CIE) coordinates and toxicity. In addition the search for non-toxic materials to replace environmentally suspect or damaging species is presently at the top of the research agenda within the European research area. For such a goal to be realized effective alternatives to materials already in use or non-toxic materials that complement and that may be incorporated into present technologies must be sought.

Project aims

• Synthesise high quality white light emitting Cu:Mn-ZnSe doped QDs with greater stability
• Find successful strategies for the transfer of the doped QDs from the non-polar media in which they are synthesised to a polar (aqueous) medium without hampering their emission profile
• Study their complex optical properties in order to gain a fuller understanding of the precise processes responsible for the instability of the doped QDs
• Fabricate solid state thin films from these doped QDs and assess the ensemble effects on their white light emission properties
• Extend the synthesis technique to develop other types of multiple doped QDs