In the history of semiconductor physics, CuO is one of the most studied materials, and many experimental semiconductor applications have been demonstrated first in this material:
*Semiconductor
*Semiconductor diodes
*Phonoritons ("a coherent superposition of exciton, photon, and phonon")
The lowest excitons in CuO are extremely long lived; absorption lineshapes have been demonstrated with neV linewidths, which is the narrowest bulk exciton resonance ever observed.  The associated quadrupole polaritons have low group velocity approaching the speed of sound. Thus, light moves almost as slowly as sound in this medium, which results in high polariton densities.
Another unusual feature of the ground state excitons is that all primary scattering mechanisms are known quantitatively. CuO was the first substance where an entirely parameter-free model of absorption linewidth broadening by temperature could be established, allowing the corresponding absorption coefficient to be deduced. It can be shown using CuO that the Kramers–Kronig relations do not apply to polaritons.