Phase formation evolution and upconversion luminescence properties of LaOF:Yb3+/Er3+ prepared via a two-step reaction

Rhombohedral and tetragonal LaOF and LaOF:Yb3+/Er3+ have been successfully prepared via a two-step reaction, which includes a facile hydrothermal method and the following heat treatment of the as-prepared LaF3 precursor. The phase formation evolution from LaF3 to LaOF with different phase structures was characterized by X-ray diffraction (XRD). The upconversion (UC) luminescence properties of rhombohedral LaOF:Yb3+/Er3+ have been investigated by the pumping power dependent UC emission spectra. Strong green and weak red UC emissions centered at 533 (544) and 669 nm were observed, respectively. The two-photon process was confirmed to be responsible for both the green and red UC emissions.