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 (Ln(3+)) doping to achieve desirable optical properties for various bioapplications. Herein, we report a novel strategy for the synthesis of sub-10 nm Ln(3+)-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 H-2(11/2) and S-4(3/2) 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:Ln(3+) nanoprobes for versatile bioapplications. (C) 2019 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.