A far-red emitting phosphor for cathode ray tubes used in liquid crystal light valves comprises lithium aluminum (or gallium) oxide, activated with iron or chromium. Increasing the activator concentration from 0.005 mole (commercially available) to about 0.015 to 0.05 mole increases the phosphor efficiency by about 50% and reduces the decay time from 30 msec (for the commerically available material) to 19 msec. Reducing the particle size to an average of 4 .mu.m or less provides the requisite high resolution for the CRT application.