Color modification of ZnGa2O4:Yb3+,Er3+,Tm3+ upconversion phosphors with the doping of Sn4+ and Ge4+ ions

Upconversion phosphors Z n 3 G a 2 S n x G e 1 − x O 8 : Y b 3 + , E r 3 + , T m 3 + were prepared by solid-state reaction with a subsequent thermal treatment at 1300°C. Under the excitation of a 980 nm laser, all phosphors produced blue emission at 477 nm, green emissions at 526 nm and 549 nm, and red emissions at 659 nm and 694 nm. The doping of S n 4 + ions and G e 4 + ions had no effect on the positions of upconversion emission peaks. However, the emission intensity changed in different degrees with different doping ions in the matrix. According to the basic theory of color-light, it is known that the color-light can be obtained by mixing a definite ratio of red, green, and blue emissions. Specifically, in the 980 nm light excitation, ZGO:Yb,Er,Tm phosphors show purplish pink luminescence, while ZGSO:Yb,Er,Tm show greenish blue luminescence, ZGGO:Yb,Er,Tm show purplish blue luminescence, and ZGGSO:Yb,Er,Tm show blue luminescence. In other words, doping S n 4 + ions can move upconversion luminescence toward the green region, while doping G e 4 + ions bend it toward the blue region. Adjusting the doping of S n 4 + ions and G e 4 + ions can obviously change the upconversion luminescent color. Besides, the upconversion luminescence of all as-prepared phosphors is visible to the naked eye without additional optical instruments.