Double-layer metasurface boosts photon up-conversion

Photon up-conversion occurs when two or more long-wavelength photons are absorbed and converted to one emitted photon with a shorter wavelength. The process has many medical and technological applications, such as biological imaging and sensing, solar energy, and photodynamic therapy for cancer treatment.

Given that certain surfaces with optical resonances can locally increase light intensity, thereby improving up-conversion efficiencies, Manley et al. wanted to explore whether multiple layers of surface structuring would lead to further progress. They used a combined approach of simulation and experiment to study the interaction of enhanced near-fields with lanthanide-doped up-conversion particles deposited on a double-layer metasurface.

The researchers constructed the metasurface with a method based on nanoimprint lithography, and a polymer film containing the up-converting particles was spin-coated onto the metasurface. For characterization, they employed spectrally and angularly resolved transmission, as well as power-dependent fluorescence measurements. In addition, the researchers solved Maxwell’s equations numerically to obtain the transmission, local field distribution, and local intensity enhancement to compare with experimental values.

Despite only 1% of the material being exposed to enhanced near-fields, the researchers observed an impressive 2.7-fold enhancement in up-conversion photoluminescence compared to a planar silicon surface. The additional layer to the metasurface enhanced a resonance called the Rayleigh-Wood anomaly that occurs when diffraction orders of a grating reach a diffraction angle of 90 degrees.

Increasing the number of layers up to four revealed these intense narrowband resonances split into a multitude of intense resonances. This allows the metasurface to potentially work over a larger range of wavelengths, making them important for applications like a solar energy, since the solar spectrum is very broadband.

Source: “Double-layer metasurface for enhanced photon up-conversion,” by Phillip Manley, Michele Segantini, Doguscan Ahiboz, Martin Hammerschmidt, Georgios Arnaoutakis, Rowan William MacQueen, Sven Burger, and Christiane Becker, APL Photonics (2021). The article can be accessed at http://doi.org/10.1063/5.0040839 .