Plasmonic array paves way forward for more efficient directional white light generation

When directional output is required, current light sources that combine blue LEDs and yellow phosphors are equipped with bulky optical elements. This approach, however, creates optical loss, decreases the output intensity and limits the design. New work in the field of plasmonics looks to provide a smaller, more efficient solution for such applications.

Kamakura et al. report findings from a newly designed light source that uses a periodic array of metallic nanocylinders to generate directional white light without the bulky optics normally required by LEDs. By applying a blue laser to an aluminum nanocylinder array on a 200-micrometer-thick yellow phosphor plate, the authors have generated quasi-white light whose color temperature correlated with 4,900 kelvins.

The device, which traps light and radiates it into desired directions, provides a step toward efficient and compact devices capable of acting as directional light sources free of bulk optics. The resulting device was able to enhance the intensity by a factor of five in the forward direction, and further up to a factor of seven after affixing a multilayer dichroic mirror on the back side of the plate, and achieved conversion efficiencies as high as 90 lm/W.

“By converging light into one direction, the intensity of yellow light is increased by seven times at normal direction by the array,” said Shunsuke Murai, an author on the paper. Thus it becomes a more efficient and directional light source thanks to the presence of the array, Murai said.

Murai said he hopes to next systematically explore other parameters in array design, including array patterns, cylinder shape and materials.

Source: “Enhanced photoluminescence and directional white-light generation by plasmonic array,” by Ryosuke Kamakura, Shunsuke Murai, Yusuke Yokobayashi, Keijiro Takashima, Masaru Kuramoto, Koji Fujita, and Katsuhisa Tanaka, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5050993 .