Synthesis and luminescence properties of Er-doped and Er/Yb-codoped CoAl 2 O 4 pigments

Abstract The development of methods to obtain ceramic pigments with fluorescence characteristics or hyper-domain performance has attracted research interest. In this study, Er-doped and Er/Yb-codoped CoAl 2 O 4 pigments were synthesized by co-precipitation. The influence of Er doping, Er/Yb codoping, and the doping contents on the colour, composition, and luminescence properties of CoAl 2 O 4 pigments were investigated. Er doping did not significantly affect the phase composition and colour performance of the CoAl 2 O 4 pigment. The upconversion effect was induced by excitation with a 950 nm laser. Er doping could enhance the upconversion luminescence intensity of the CoAl 2 O 4 pigment. At a 1 mol.% Er doping content, all luminous intensities reached maximum values. The downconversion effect was observed after excitation with a 350 nm laser. The luminescence was blue, and slight differences in the luminescence intensity with different Er doping contents were observed. Yb 2 O 3 was formed after Er/Yb was codoped at > 6 mol.% Yb doping content, thereby affecting the phase composition and colour performance of the CoAl 2 O 4 pigment. The luminous intensity of red light (739 nm) was the strongest in all cases. The luminous intensities of all of the colours decreased to the minimum value at 9 mol.% Yb doping content compared with those at other doping contents. At 3 mol.% Yb doping content, the luminous intensities of all colours decreased to very low values (close to 0), and the quenching effect of Yb 3+ was achieved using a 350 nm laser. Er/Yb-codoped CoAl 2 O 4 pigments exhibited the upconversion luminescence effect under an infrared laser and inhibited visible-light reflection under an UV laser. This ceramic pigment can be developed further to obtain ceramic pigments with anti-counterfeit function.