Temperature sensing, excitation power dependent fluorescence branching ratios, and photothermal conversion in NaYF4:Er3+/Yb3+@NaYF4:Tm3+/Yb3+ core-shell particles

Temperature controllable photothermal therapy (PTT) requires a nanoplatform in which the optical temperature sensor and photothermal calorifier are integrated together. To establish such a nanoplatform, in this work we designed a NaYF4:Er3+/Yb3+@NaYF4:Tm3+/Yb3+ core-shell structure, and studied on its temperature sensing and photothermal conversion. The core-shell nanoparticles were prepared via a thermal decomposition method; furthermore, their crystal structure and microscopic morphology were characterized by means of XRD and SEM/TEM. The properties of temperature sensing and excitation power dependent fluorescence branching ratios were investigated. It was found that the temperature sensing could be achieved based on the fluorescence intensity ratio of green emissions from Er3+, but could not be realized by using other fluorescence intensity ratios. The photothermal conversion was demonstrated under 808 and 980 nm co-excitation, and the dependences of photothermal conversion on the excitation power and irradiation time of 808 nm laser were observed. Moreover, it was also found that the core-shell particles could effectively accelerate the evaporation of anhydrous ethanol, thus implying the photothermal conversion under single 980 nm laser excitation could also be achieved. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement