Modulated upconversion luminescence of WO3: Yb3+/Ho3+ through non-equivalence substitution of Bi3+ ions

The upconversion luminescence (UCL) of inorganic materials doped with activators and sensitizers has great application, but its luminescence intensity always impose restrictions on its development. Herein, an obvious enhancement in luminescence intensity of the WO3: Yb3+, Ho3+ phosphor was realized through non-equivalence substitution of Bi3+ ions. The single pure phase of the synthesized WO3: Yb3+, Ho3+, and Bi3+ phosphors has been confirmed by the XRD pattern. The morphology of phosphors and valence state of elements have been performed by SEM and XPS techniques. The sample on excitation with 980 nm performs forceful green emission and weak red emission at 543 nm and 662 nm, separately. The concentrations for doped Yb3+ and Ho3+ to obtain the optimal UCL in WO3 are 8% and 1%, respectively. The optimized doping concentration for Bi3+ ions is 3%. Compared to samples without Bi3+ ions, the Yb3+/Ho3+/Bi3+ doped WO3 obtains 1.59 and 2.33 times increase in emission intensity of green and red, respectively. We also explored the UCL mechanism and enhancement mechanism on the basis of the power dependency, the UCL and the downshift luminescence. These results based on Yb3+/Ho3+ UCL phosphors research is of great significance.