Sub-10 nm lanthanide-doped SrFCl nanoprobes: Controlled synthesis, optical properties and bioimaging

Alkaline-earth dihalide nanocrystals (NCs) such as SrFCl, owing to their high chemical stability and low phonon energy, are excellent host materials for lanthanide (Ln3+) doping to achieve desirable optical properties for various bioapplications. Herein, we report a novel strategy for the synthesis of sub-10 nm Ln3+-doped SrFCl NCs with efficient upconverting and downshifting luminescence through a facile one-step hot-injection method. Utilizing the temperature-dependent upconverting luminescence (UCL) from the thermally coupled 2H11/2 and 4S3/2 levels of Er3+, we showed the potential of SrFCl:Yb,Er NCs as sensitive UCL nanoprobes for non-contact thermal sensing with a maximum detection sensitivity of 0.0066 K–1, which is among the highest values for thermal sensing based on Er3+-activated UCL nanoprobes. Furthermore, by employing the intense downshifting luminescence from Tb3+ and Eu3+, we demonstrated the successful use of biotinylated SrFCl:Ce,Tb and SrFCl:Eu3+ nanoprobes for biotin receptor-targeted cancer cell imaging, thus revealing the great promise of SrFCl:Ln3+ nanoprobes for versatile bioapplications.