Manipulating energy migration in nanoparticles toward tunable photochromic upconversion

Smart control of energy interactions plays a key role in manipulating upconversion dynamics and tuning emission colors for lanthanide-doped materials. However, quantifying the energy flux in particular energy migration in the representative sensitizer-activator coupled upconversion system has remained a challenge. Here we report a conceptual model to examine the energy flux in a single nanoparticle by designing an interfacial energy transfer mediated nanostructure. We show that energy migration indeed occurs simultaneously with energy transfer in a sensitizer-activator system and the competition between them can be quantified by proposing a characteristic ratio parameter. Moreover, this model is also able to realize the color-switchable photochromic upconversion by temporal control of up-transition processes. These findings offer a deep insight into the understanding of upconversion dynamics and provide a versatile approach to manipulating the energy flux in nanostructures with tunable emission colors, showing great promise in applications of logic operation and information security. Upconversion nanoparticles can produce emission via sensitizer-activator energy transfer or by energy migration along the interlayer sublattice. Here, the authors quantify their competition and use it to realize color tunability.