Synthesis and upconversion luminescence properties of CaF₂:Yb³⁺,Er³⁺ nanoparticles obtained from SBA-15 template

CaF₂:Yb³⁺,Er³⁺ upconversion (UC) luminescence nanoparticles have been synthesized using mesoporous silica (SBA-15) as a hard template. The samples were characterized by x-ray diffraction, Fourier transform infrared spectra, field-emission scanning electron microscopy, transmission electron microscopy, and UC emission spectra, respectively. Highly crystalline cubic phase CaF₂:Yb³⁺,Er³⁺ nanoparticles are uniformly distributed with an average diameter of about 40–50 nm, and the formation process is also demonstrated. The UC fluorescence has been realized in the as-prepared CaF₂:Yb³⁺,Er³⁺ nanoparticles on 980-nm excitation. The UC emission transitions for ⁴F_9/2–⁴I_15/2 (red), ²H_11/2–⁴I_15/2 (green), ⁴S_3/2–⁴I_15/2 (green), and ²H_9/2–⁴I_15/2 (violet) in the Yb³⁺/Er³⁺ codoped CaF₂ nanoparticles depending on pumping power and temperature have been discussed. The UC mechanism, especially the origin on the temperature-dependent UC emission intensities ratio between ²H_11/2 and ⁴S_3/2 levels, have been proposed.