Fabrication of upconversion emissive LaOCl phosphors doped with rare-earth ions for bioimaging probes

Lanthanum oxychloride nanoparticles containing trivalent erbium ions were prepared through a self-hydrolysis process of hydrated chlorides of lanthanum and erbium. The phosphors were characterized by X-ray diffraction to be found in a single oxychloride phase. Irradiation on the powder with a 980-nm laser diode resulted in frequency upconversion into intense green emissions around 525-550 nm and red emissions around 650670 nm. Stokes emission and excitation power dependence of the upconversion emission were also measured, and the dominant upconversion mechanisms were deduced to be the excited state absorption (ESA) and phonon-assisted energy transfer (PET) for green and red emissions, respectively.