Room-temperature holographic grating recording in CdF2:Ga

We demonstrate that semiconducting ${\mathrm{CdF}}_{\mathrm{2}}$ crystals doped with gallium provide an efficient medium for optical storage of information in static and dynamic regimes in a temperature range close to 300 K. Ga is a bistable center in ${\mathrm{CdF}}_{\mathrm{2}}$ crystals. Illumination by visible and UV light below 500 nm causes phototransformation of these centers from a deep-localized to a shallow-hydrogenic state. They are separated by a vibronic barrier that causes metastability below 250 K. The phototransformation changes the local polarizability, and thus, the local refractive coefficient. This, in turn, allows writing a phase hologram with a diffraction efficiency and decay time being temperature dependent with the activation energy $E_{\mathrm{act}}\text{=0.65±0.1\hspace{0.17em}}\mathrm{eV}.$ A spontaneous decay of the grating is caused by a thermal recovery of the Ga impurity from the metastable hydrogenic state to the localized ground state. The writing is a local process.