The first spectroscopic measurements ofR′ aggregate color centers contained in polycrystalline LiF hosts are reported. The inhomogeneous and homogeneous widths of the 830‐nm zero phonon line are measured by conventional grating spectroscopy and by photochemical hole burning spectroscopy using a current tuned GaAlAs diode laser with 3‐mW output power. An extensive photochemical hole burning comparison between single and polycrystalline samples is presented.