Reduction of Eu2+-activated nanoparticles by unique TCRA treatment

The Eu2+ ion-doped CaF2 nanoparticles were synthesized by means of the sol–gel method. As prepared, the typical luminescence due to the intra 4f–f transitions of only Eu3+ ion was observed. The TCRA (thermal-carbon reducing atmosphere) treatment using activated carbon realized efficient reduction from Eu3+ to Eu2+ ions. Afterward TCRA treatment, a strong and broad luminescence with the peak at 425 nm due to the parity allowed 4f7–4f65d1 transition of Eu2+ ion was observed. The average size of particles as estimated using XRD patterns proportionally increased from 15 to 120 nm with increasing heating temperatures from 300 to 700 °C. The particle sizes were evaluated by the AFM morphologies exhibiting a good accordance with the results from XRD.