Intensifying Upconverted Ultraviolet Emission towards Efficient Reactive Oxygen Species Generation

Multiphoton upconversion that can convert near-infrared irradiation into ultraviolet emission offers many unique opportunities for photocatalysis and phototherapy. However, the high-lying excited states of lanthanide emitters are often quenched by the interior lattice defects and deleterious interactions among different lanthanides, resulting in weak ultraviolet emission. Here, we describe a novel excitation energy lock-in approach to boost ultraviolet upconversion emission in a new class of multilayer core-shell nanoparticles with a gadolinium-rich core domain. Remarkably, we observe more than 70-fold enhancements in Gd3+ emission from the designed nanoparticles compared with the conventional nanoparticles. Our mechanistic investigation reveals that the combination of energy migration over the core domain and optically inert NaYF4 interlayer can effectively confine the excitation energy and thus lead to intense multiphoton ultraviolet emission in upconversion nanostructures. We further achieve a 35.6% increase in photocatalytic reactivity and 26.5% in reactive oxygen species production yield in ZnO-coated upconversion nanocomposites under 808-nm excitation. This study provides a new insight to energy transfer mechanism in lanthanide-doped nanoparticles and offers an exciting avenue for exploring novel near-infrared photocatalysts.

Automated summary

This study introduces a novel excitation energy lock-in approach to enhance ultraviolet upconversion emission in nanoparticles. The results show that confining the excitation energy within the core domain and using an optically inert interlayer can significantly boost multiphoton ultraviolet emission. Moreover, the study demonstrates improved photocatalytic reactivity and reactive oxygen species production in ZnO-coated upconversion nanocomposites under 808-nm excitation.