Titanium oxides were found to significantly enhance efficiency and photoluminescence in a recent study.
White LEDs’ reign as the top light source may soon come to an end with the advent of a new alternative that offers superior directionality.
A photonic crystal or nanoantenna, a 2D structure with periodic arrangement of nano-sized particles, is being developed as a cutting-edge optical control technology. Upon exposure to light, combining a nanoantenna with a phosphor plate produces a harmonious mix of blue and yellow light.
White LEDs have already been improved upon in the form of white laser diodes, or LDs, which consist of yellow phosphors and blue LDs. While the blue LDs are highly directional, the yellow phosphors radiate in all directions, resulting in an undesired mixing of colors.
To address this issue, researchers have developed phosphor plates combined with nanoantennas using metallic aluminum, enabling increased photoluminescence. Aluminum nanoparticles effectively scatter light and improve light intensity and directionality; however, aluminum also absorbs light, reducing the output. This is a major bottleneck, especially in high-intensity lighting applications.
Now, a team of researchers at Kyoto University has achieved a ten-fold enhancement of forward-directed photoluminescence by replacing aluminum with a better material.
“It turns out that titanium dioxide is a better choice for its high refractive index and low-light absorption,” says lead author Shunsuke Murai.
Although the light-scattering intensity of titanium oxide initially appeared inferior to metallic aluminum, the team used computer simulations to devise the optimal nanoantenna design.
“The new nanoantenna phosphors are advantageous for intensely bright yet energy-saving solid-state lighting because they can suppress temperature rise when irradiated,” explains Murai.
“During the process of finding the optimal dimensions, we were surprised to discover that the thinnest phosphors gave the brightest photoluminescence, demonstrating how to increase the forward radiation intensity and overall performance.”
Reference: “Photoluminescence engineering with nanoantenna phosphors” by Shunsuke Murai, Feifei Zhang, Koki Aichia and Katsuhisa Tanaka, 21 December 2022, Journal of Materials Chemistry C.
The study was funded by Kakenhi.