When incorporated into Gd2O2S (if this is possible based on the similarity between the ionic radii of the dopant and Gd3+), the ions you mention will be in the Cs+ and In3+ valence state. Then, these ions have a closed valence shell configuration. E.g. Cs+ has the Xe electronic configuration. Consequently, the first excited state - obtained by promoting an electron to an unoccupied shell, is too high in energy to give near-UV or visible emission. Similarly, In3+ has a closed 4d10 configuration.

When synthesized, these phosphors might give some luminescence, especially when defects are expected to be formed. E.g. 'forcing' Cs+ onto a Gd3+ lattice site will lead to charge compensating defects which can induce some luminescence, although often with low efficiency. 

Thanks dear Philippe. it was very useful.

terbium (Tb) is mostly used as activator in gadolinium oxisulfide  detectors