Lithium Niobate Nanocubes as Linear and Nonlinear Ultraviolet Mie Resonators

Many dielectric and semiconductor materials used for all-dielectric resonators or metasurfaces have low absorption in the near-infrared to visible range, but they are lossy in the near-ultraviolet (NUV) range due to their low energy band gap. Contrary to this, the ferroelectric lithium niobate (LiNbO3, LNO) has an energy band gap larger than 4 eV and, consequently, very low losses in the NUV range down to 310 nm. Here, we propose LNO nanocubes as a new alternative material for nonlinear photonics in the NUV range. We report that LNO nanocubes fabricated by solvothermal synthesis with sizes from 200 to 300 nm demonstrate strong second harmonic generation (SHG) emission below 400 nm due to Mie resonances, with an SHG enhancement of 10(7) compared to bulk LNO at 360 nm. The LNO nanocubes presented in this work are novel efficient all-dielectric Mie resonant nanostructures for the NUV with a wide range of possible photonic applications, from nanophotolithography to metasurfaces and complex assemblies of nanostructures or nano-optical modulators.