INFRARED PHOSPHOR AND MATERIAL HAVING LATENT IMAGES AND OPTICAL READING SYSTEM USING SAID PHOSPHOR

摘要

The invention provides a phosphor excited by infrared rays to emit infrared rays which has a particle shape of nonacicular and a particle size of 4 .mu.m or smaller after synthesized. The phosphor preferably comprises an oxoacid salt-containing compound containing at least one element selected from the group consisting of Nd, Yb and Er. The invention further provides a material having a latent image pattern comprising said phosphor and an optical reading system which use the material having a latent image pattern.