Researchers obtain more light from LEDs thanks to nanoparticle
Researchers from the FOM institute AMOLF and Philips Research have increased the light intensity of white LEDs in certain directions by up to sixty times. The physicists achieved this by combining the normal fluorescent layer in LEDs with a structure of metal nanoparticles. The results of their research were published on 10 May in the new journal Light: Science & Applications from the Nature Publishing Group.
The development of efficient LED light sources is the most important step towards energy efficient lighting. For a LED to emit white light you first of all need an efficient blue LED. This blue LED illuminates a layer of fluorescent material – a so called phosphor. The layer absorbs a part of the blue light and converts this into light with a different colour. The light that the phosphor emits is subsequently combined with the non-absorbed part of the light, giving rise to white light. The LED transmits this white light in all directions. Focusing the light requires the use of lenses or mirrors and that reduces the efficiency of the white LED. Furthermore, mirrors and lenses are expensive.
The researchers from AMOLF and Philips Research have found a solution for this. They placed the phosphor on top of a grating of aluminium nanoparticles. These nanoparticles support resonances that arise in the free electrons in the metal and that facilitate the fluorescence of the phosphor. The resonances reinforce each other, which results in a more efficient uptake of the blue light by the phosphor and hence to a greater emission of white light.
By varying the distance between the nanoparticles in the grating the researchers could also control the preferred direction of the light emitted. With this approach the researchers achieved a 60-times stronger light emission in some directions than in a conventional LED.
This exceptional strengthening of the light intensity provides new possibilities for efficient lighting in which metal nanostructures determine the light intensity and angle of light emission.
Reference
G. Lozano, D.J. Louwers, S.R.K. Rodriguez et al., Plasmonics for solid-state lighting: enhanced excitation and directional emission of highly efficient light sources . Light: Science & Applications 2, e66 (2013) | DOI:10.1038/lsa.2013.22
Contact information
Gabriel Lozano, +31 (0)40 274 29 64
Jaime Gómez Rivas, +31 (0)40 274 23 49