How the surface-processing conditions affect the intrinsic luminescence of CsI crystals

It is shown that luminescence of CsI crystals with wavelength λem=305nm is observed at room temperature when it is excited in the long-wavelength exciton-absorption band at λex=220nm. To excite this luminescence close to the surface, two factors need to be taken into account when fabricating the samples. First, the temporal character of the relaxation of the damaged layer; second, the penetration of quenching impurities into the near-surface layer during the diffusion escape of surplus vacancies onto the free surface. The intrinsic photoluminescence of CsI crystals was observed earlier only in the two-photon absorption regime, when the crystal was transparent to the exciting light. To minimize the number of defects in the near-surface layer, chemical polishing of the surface is proposed, carried out after the damaged layer relaxes.