By using a simple low-temperature supercritical fluid-assisted method, single-crystalline nanoribbons coated with crystalline multisheath oxide have been successfully synthesized, with a nominally uniform coating over the entire outer surface of the nanoribbons. The methodology reported here is highly versatile. As an example, Ga2O3-Eu2O3 core-sheath coaxial nanoribbons are synthesized and show a novel energy transfer between the core and sheath at room temperature, which is observed for the first time in our study. The structures are confirmed by HRTEM, EDX, and XPS. These core-sheath coaxial heterostructures, with their various possible functionalities, represent an important new class of nanoscale building blocks for optoelectronic applications.