Enhanced upconversion luminescence in LuPO4:Ln3+ phosphors via optically inert ions doping

The upconversion luminescence (UCL) properties of Yb3+/Ho3+ (Er3+) co-doped or tri-doped LuPO4 phosphors were studied and compared. To further improve the UCL intensity and control the emission color, optically inert ions such as Li+, Ca2+ and Gd3+ were doped into this system. Compared to the optically inert ions-free counterpart, the red UCL of LuPO4:20%Yb3+/1%Er3+/1%Ho3+ with 5%Li+/10%Ca2+/10%Gd3+ doping is enhanced by 5.93 times. It is worth pointing out that the optically inert ions doping could not change the red-to-green intensity ratio. Therefore, the emission color was still maintained irrespective of the type of optically inert ions used for doping. Moreover, the reasons for the above experimental phenomenon were also discussed in detail.