ZnCdS:Cu,Al,Cl: A Near Infra-Red Emissive Family of Phosphors for Marking, Coding, and Identification

© Copyright The Author(s) 2017. Zn1-xCdx:Cu0.03%,Cl (where x = 0.5–0.9) infrared emitting phosphors have been synthesized by an aqueous thermal decomposition method. The aim was to developing infrared emitting phosphors for coding, marking, and identification applications. The phosphors were characterized by, X-ray powder diffraction, scanning electron microscopy and photoluminescence spectroscopy. The emission \nband at 1000 nm was sufficiently far into the infrared region that visible emission was minimized. Co-doping Zn1-xCdxS:Cu0.03% with Al3+ increased the infrared emission intensity to over twice that of the equivalent Zn0.3Cd0.7S:Cu0.03% phosphor (with no Al3+ ion co-doping), with the highest intensity being found for the phosphor composition Zn0.1Cd0.9S:Cu0.03%, Al0.03%. It is shown herein that the inclusion of Al3+ into the phosphors causes the formation of cells with smaller cell volume, and it is suggested that this is the prerequisite for the improved photoluminescent properties. Finally we have shown herein that these infrared emitting powder phosphors are thus able to meet marking and coding requirements, especially in low light and poor visibility.