Syntheses of CaF2:Eu nanoparticles and the modified reducing TCRA treatment to divalent Eu ion

The Eu ion-doped CaF2 nanoparticles were synthesized by the sol–gel method using the trifluoro-acetic acid (TFA). The prepared samples were characterized with the XRD (X-ray diffraction), PL (photoluminescence), PLE (photoluminescence excitation) and AFM (atomic force microscopy) observation. It was calculated that the crystalline size increased from 15 to 120 nm depending on the sintering temperature. The typical luminescence of only Eu3+ ion was observed at 575, 591, 611 and 625 nm on as-prepared sample. It was found that the effective reduction from Eu3+ to Eu2+ ions was realized by modified reducing method based on the TCRA (thermal-carbon reducing atmosphere) treatment. The intense and broad luminescence due to the parity allowed 4f7–4f65d1 transition of Eu2+ ion was observed at 425 nm after reduction. The surface image showed that the uniform grains grew up to 120 nm depending on the heating temperatures from 500 to 700 °C and the grain sizes agreed well with the crystalline sizes calculated from XRD measurements.