Lanthanide-doped LaOBr nanocrystals: controlled synthesis, optical spectroscopy and bioimaging

Lanthanide (Ln3+)-doped nanocrystals (NCs) have shown great promise in diverse bioapplications. Exploring new host materials to realize efficient downshifting (DS) and upconversion (UC) luminescence is a goal of general concern. Ln(3+)-doped oxybromides, which bring together the advantages of high chemical/thermal stability of oxides and low phonon energy of bromides, have been rarely reported so far. Herein, we report the synthesis of monodisperse tetragonal-phase LaOBr: Ln(3+) NCs via a modified thermal decomposition approach. Ln(3+) dopants in LaOBr NCs occupying surface and lattice sites were verified based on high-resolution photoluminescence spectra of Eu3+ at 10 K. Intense DS emissions were observed in Ce3+ and Ce3+/Tb3+ doped LaOBr NCs upon excitation at 353.0 nm, which is far from the deep-UV absorption band of proteins. Moreover, UC properties of LaOBr: Yb3+/Ho3+ and Yb3+/Er3+ NCs were comprehensively surveyed upon near-infrared excitation at 980 nm. Particularly, the red-togreen ratio can be markedly increased from 0.1 to similar to 300 in LaOBr: Yb3+/Er3+ NCs, resulting in high-chromatic-purity single-band red UC emission. Furthermore, we have employed the LaOBr: Ln(3+) NCs for cancer cell imaging by virtue of their superior optical properties, showing great potential of LaOBr:Ln(3+) nanoprobes in bioimaging.