A series of CaxSr1-xS : Te samples with 0 < x < 1 were grown from Te solutions to a size of 100 x 100 x 50 mu m(3). Te concentrations in CaxSr1-xS : Te measured with an electron-probe microanalyser ranged from 0.01 to 0.2 mol%. The cathodoluminescence peak energy depends on x as a function of 3.3396 + 0.079x - 0.395x(1 - x) eV at room temperature. Two photoluminescence peaks were observed in the spectra at 77 K, the x dependence of the high-energy peak was 3.527 + 0.074x -0.463x(1 - x) eV and that of the low-energy peak was 3.137 - 0.077x -0.596x(1 - x) eV. Corresponding to the two emission peaks, two photoluminescence excitation peaks were observed with the x dependence of 3.995 + 0.139x - 0.099x(1 - x) and 3.827 + 0.060x - 0.082x(1 - x) eV, respectively, at 77 K. Broad emission bands and large Stokes shifts are features of the localized centers. As the exciton trapping energy of CaxSr1-xS : Te has a weak a dependence, which is predicted based on the isoelectronic tray theory, the origin of the luminescence is assigned to the Te isoelectronic trap centers.