Synthesis of core-shell nanoparticles based on interfacial energy transfer for red emission and highly sensitive temperature sensing.

Red up-conversion luminescence with both emission and excitation peaks within the "tissue transparency window" makes for ideal fluorescent labels for deep tissue penetration and low-background biological imaging. In this work, an efficient strategy is proposed to realize bright red up-conversion luminescence based on interfacial energy transfer (IET), and the luminescence centers (Er 3+ and Tm 3+ ) and sensitizers (Yb 3+ ) are doped in separate layers to avoid deleterious cross-relaxation. The IET process between Yb 3+ and Er 3+ can enable bright red photon up-conversion under 980 nm excitation via fine control and manipulation of the lanthanide ion concentration and shell thickness. By appropriately employing the fluorescence intensity ratio technique, an optical thermometer based on non-thermally coupled energy levels demonstrates a superior relative sensitivity of 2.02% K -1 across the whole temperature region. NaYF 4 :Er 3+ ,Tm 3+ @NaYF 4 :Yb 3+ with strong red UC luminescence and highly sensitive performance exhibits potential for application in the field of non-contact temperature sensing.