A material being readable by machine is a powder substance made of Eu2O3 doped with RE2O3 as its proportioning relation is RE2O3:Eu2O3=2:40:1. The average particle diameter of powder is less than 5 micron and red visible fluorescent light can be issued under trigger from shortwave ultraviolet ray with persistence lifetime of 5 milisecond and below. The preparing process includes preparing rare-earth oxide-entering transrate earth ion into liquid phase-separating out precipitated salt from liquid phase-sintering separated out material to be rare earth oxide.