A broadening temperature sensitivity range with a core-shell YbEr@ YbNd double ratiometric optical nanothermometer

The chemical architecture of lanthanide doped core-shell up-converting nanoparticles can be engineered to purposely design the properties of luminescent nanomaterials, which are typically inaccessible to their homogeneous counterparts. Such an approach allowed to shift the up-conversion excitation wavelength from similar to 980 to the more relevant similar to 808 nm or enable Tb or Eu up-conversion emission, which was previously impossible to obtain or inefficient. Here, we address the issue of limited temperature sensitivity range of optical lanthanide based nano-thermometers. By covering Yb-Er co-doped core nanoparticles with the Yb-Nd co-doped shell, we have intentionally combined temperature dependent Er up-conversion together with temperature dependent Nd. Yb energy transfer, and thus have expanded the temperature response range Delta T of a single nanoparticle based optical nano-thermometer under single similar to 808 nm wavelength photo-excitation from around Delta T = 150 K to over Delta T = 300 K (150-450 K). Such engineered nanocrystals are suitable for remote optical temperature measurements in technology and biotechnology at the sub-micron scale.