Epitaxial KNbO₃:Yb³⁺,Er³⁺ nanopattern for enhanced upconversion photoluminescence

Nanopatterned epitaxial films of upconversion (UC) materials are desirable for various applications such as display lighting, waveguides, and optical imaging. In this study, we demonstrate that a nanopatterned epitaxial film of a UC material can be fabricated by combining a sol–gel process and nanoimprint lithography. An epitaxial KNbO₃:Yb³⁺,Er³⁺ film is grown on a lattice-matched SrTiO₃ single-crystal substrate, which exhibits an approximately 70 times enhanced UC photoluminescence (PL) intensity compared to that of a non-epitaxial KNbO₃:Yb³⁺,Er³⁺ film grown on a Si substrate. Moreover, the introduction of a nanopattern enhances the UCPL intensity ∼20 times compared to that of a planar film with the same volume of material. Our study paves the way for a better fundamental understanding and expansion in the application of UC materials.