An innovative approach to photolithography for optical recording of high-resolution two-dimensional structures in a negative SU8 photoresist by activation of up-conversion luminescence in Yb[formula omitted] and Tm[formula omitted] doped NaYF[formula omitted] nanoparticles

Abstract

In this work, we demonstrate the success of an innovative approach to photolithographic recording of high-resolution 2D structures in thin films of hybrid inorganic nanoparticles/photoresist systems. This is done by utilising Yb3+, Tm3+ up-conversion luminescence in core–shell (β-NaYF4:Yb3+, Tm3+/ β-NaYF4)-structured nanoparticles (33.9 nm in size) mixed into a negative photoresist SU8. This approach is a promising alternative compared to traditional optical lithography performed by i-line UV radiation through a surface. Specially designed core–shell-structured nanoparticles were synthetised to emit Tm3+-characteristic up-conversion luminescence bands in the UV spectral region at 345 and 361 nm, and in the blue spectral region at 450 and 476 nm under IR excitation at 976 nm. The exposed elliptically shaped uniform structure, with dimensions of ∼160 ×320μm, was recorded in a ∼500 nm thin photosensitive layer by 1–5 min long infrared exposure when core–shell nanoparticles doped with Yb3+ and Tm3+ ions were mixed into negative photoresist SU8. Such hybrid systems of organic chromophores/UCNP/SU8 are highly prospective for the fabrication of various types of microstructures without damaging the light-sensitive organic compound, which is required in medicine (microsurgery, laboratory on a chip, etc.), telecommunications, military, sensor technologies and a wide range of photonic applications, e.g. for the fabrication of micro disk resonators used as active media in organic solid-state lasers.