PURPOSE: A fluorescent substance for cathode ray tubes, consisting of a zinc silicate fluorescent substance, containing a very small amount of bismuth, and activated with manganese having a specific composition, not easily affected to cause electron ray damages by the stimulation by the electron rays with a slight deterioration in brightness.

CONSTITUTION: A fluorescent substance for cathode ray tubes, having a composition expressed by the formula (a is 2W1.8; b is 0.01W0.07; c is 0.00015W0.0015), and containing a very small amount of bismuth. The degree of the electron ray damages is obtained as follows: The brightness before the irradiation with stimulation of electron rays at 15kV voltage, 0.6μA/cm2 current density and 0.7cm square luster size is measured. The burning is obtained by measuring the brightness after the irradiation with stimulation of electron rays at 1.5kV, 10μA/cm2 current density of 10 times of the above-mentioned test and 1cm square luster for 30min. The degree of electron ray damages are smaller when the ratio of the brightness before and after the irradiation is closer to 1.