Abstract: A kind of Co_xR_1-xAl₂O₄(R=Zn、Mg，x=0.8\sim1.0)cobalt blue pigment suitable for luminophor of color televisions was synthesized successfully by
using the chemical coprecipitation method. Compared with CoAl₂O₄ reflectivity, the increase of reflectivity of Co_xR_1-xAl₂O₄ is 18.2% at 450nm
and --5% at 600nm respectively. Through discussing some affecting factors on this kind of pigment such as doping cation type, doping content and Co²⁺
content, a conclusion can be drawn that the mechanism of reflectivity properties alteration of complex cobalt blue pigments caused by doping cations Zn²⁺,
Mg²⁺ is Co²⁺3d electronic energy level cleavage due to lattice distortion. The lower limit value of x of Zn²⁺, Mg²⁺ is 0.85 and 0.8 respectively.

Key words: Co_xR_1-xAl₂O₄ pigment, reflectivity properties, doping cation