  Efficient, low noise conversion between different colors of light is a
necessary tool for interfacing quantum optical technologies that have different
operating wavelengths. Optomechanically mediated wavelength conversion and
amplification is a potential method for realizing this technology, and is
demonstrated here in microdisks fabricated from single crystal diamond--a
material that can host a wide range of quantum emitters. Frequency
up--conversion is demonstrated with internal conversion efficiency of $\sim$45%
using both narrow and broadband probe fields, and optomechanical frequency
conversion with amplification is demonstrated in the optical regime for the
first time.
