Enhanced upconversion luminescence in layered Bi2GdO4Cl:Yb3+/Er3+ by reducing OVs and its application in photocatalysis

Internal lattice defects are one of the main detrimental factors affecting the upconversion (UC) luminescent efficiency of layered bismuth oxyhalide doped with rare earth ions. Unlike surface-related luminescence quenching which can be effectively suppressed by surface passivation, internal lattice defects are easily generated during the material preparation but are difficult to be controlled and diminished. Therefore, it becomes an obstacle to improving the luminescent intensity of bismuth oxyhalide UC materials. Herein, we report a novel Li+ doping strategy for reducing lattice oxygen vacancy (OV) defects in Bi2GdO4Cl:Yb3+/Er3+ (BYE) crystals. With Li+ doping, the morphology of the samples gradually evolves from irregular agglomerated particles to plate-like ones. The experimental and DFT calculation results show that Li (+) dopants tended to occupy lattice interlayer in the layered Bi2GdO4Cl (BGOC) while reducing the oxygen vacancies (OVs) generated during the BGOC preparation. As a result, under 980 nm excitation, BYE doped with 5 mol% Li+ (BYE-5Li) exhibits significantly enhanced UC emission, and the red and green emissions are increased by about 20 and 40 times compared with those of undoped BYE, respectively. Derived from the enhanced UC emission and separation of photogenerated carriers due to OVs reduction, the BYE-5Li exhibits the best photocatalytic activity leading to the decomposition of about 62% of TCH with the highest degradation rate k = 0.008 min(-1), which is twice that of pristine BGOC. This work not only opens new perspectives for enhancing UC luminescence of bismuth oxyhalide and promotes their application in photonics and photocatalysis fields but also offers new insights into the role of OVs in UC luminescence and photocatalysis.

Automated summary

In this study, a Li+ doping strategy is proposed to reduce lattice oxygen vacancy (OV) defects in Bi2GdO4Cl:Yb3+/Er3+ crystals, resulting in enhanced upconversion emission and improved photocatalytic activity.