Enhancing fluorescent thermo-sensitivity in Er-Tm dual-activator microrods via cooperation of partitioned doping and excitation controlling

Abstract

Lanthanide ion co-doped upconversion luminescent materials, which exhibit excellent optical properties, have significant potential applications in temperature sensing. The temperature measurement sensitivity is contingent on the doping architecture and the corresponding excitation conditions. It is therefore imperative to systematically investigate the synergistic modulation effects of these two aspects. In this study, the effects of dual-ion doping strategies (including concentration and distribution state) and excitation conditions (including excitation power density and pulse width) on upconversion luminescence and temperature sensing in micron-scale core-shell structures are systematically investigated using erbium (Er) and thulium (Tm) dual-activator doped fluoride as a model system. It has been established that, under uniform doping conditions, the energy interactions between different luminescent centres are detrimental to temperature measurement. Furthermore, under short-pulse excitation, the temperature responsiveness of the emission ratio is significantly enhanced both between thermally coupled energy levels and between double ions, despite the occurrence of the same thermal quenching phenomenon as in the continuous excitation mode. Further analysis of the temperature-dependent behaviour confirms that non-uniformly doped core-shell engineering and short-pulse excitation can significantly suppress the energy exchange process between Er and Tm, leading to highly sensitive temperature sensing. Finally, lanthanide-doped upconverted micrometer particles have been utilised for the purpose of surface temperature measurement in conjunction with 3D printing technology. The results obtained provide a comprehensive analytical solution for high sensitivity and stable temperature sensing through the optimisation of excitation patterns and spatially split doping strategies.