Multifunctional up/down-conversion luminescence of core/shell nanocomposite for self-monitored heating and fluorescence imaging

Highlights: • The C/S-4 were successfully synthesized via a stepwise metal-organic thermolysis process. • The incompatibility of the DCL and PTT is solved by energy-blocked shells. • The C/S-4 has potential application on noninvasive cancer therapy and fluorescence imaging. The simultaneous realization of real-time thermal sensing at physiological temperature range and fluorescence imaging during photothermal therapy (PTT) via single-component biocompatible nanocomposite could furthest avoid collateral damage and enhance phototherapeutic effect, which, up to now, is of great interest and still in a formidable challenge. Under near-infrared (NIR) light irradiation, Nd³⁺-doped nanoparticles (NPs) have emerged as candidates with outstanding properties such as down-conversion emissions in biological window (BW) and capable of light-to-heat conversion. However, these two properties associated with Nd³⁺ doping concentrations induce opposite changing trend and difficult to combine within one single nanocomposite. In this work, for breaking through the obstacles, core/shell NaLuF₄:1%Nd@NaLuF₄@NaLuF₄:15%Yb,3%Er@NaLuF₄:15%Yb@NaLuF₄:85%Nd 808 nm light-triggered co-enhancement up/down-conversion luminescence (UCL/DCL) nanocomposite was purposely designed with efficient heating, thermal sensing and fluorescence imaging concurrently. The core emits high quantum yield (QY) DCL in BW while the outermost layer could convert the absorbed photon into thermal energy and also transfer a fraction of energy inwards to internal layer with exciting the UCL (Nd→Yb→Er) for thermal sensing via thermally coupled levels ²H_11/2/⁴S_3/2 of Er using the fluorescence intensity ratio (FIR) method. The simultaneously enhanced UCL/DCL and thermal effect in the engineered nanocomposite are satisfactorily realized due to suppressing the interionic quenching owing to the inert two layers NaLuF₄ and NaLuF₄:15%Yb. Such smart designed nanocomposite has potential application on PTT-based noninvasive cancer therapy.