Optical Spectroscopy of Eu3+-Doped BaFCl Nanocrystals

Tetragonal Eu 3+:BaFCl nanocrystals were synthesized via mild-temperature solvothermal treatment. The size of the as-grown nanoflakes was estimated to be 100−200 nm in diameter and 20−40 nm in thickness by XRD, SEM, and TEM. By means of site-selective spectroscopy at 10 K, two kinds of luminescence sites of Eu 3+ were unambiguously identified. One site showing moderately resolved fluorescence lines was associated with the distorted lattice site that might be close to the surface. Another one exhibiting very sharp emission and excitation peaks was ascribed to the inner lattice site with an ordered crystalline environment. Intense and sharp emission lines from the excited states of 5 D 1 and 5 D 2 in Eu 3+:BaFCl nanocrystals were observed for the first time. The lifetime of 5 D 0 was significantly longer than that of the microcrystal counterpart and decreased rapidly with the increase of temperature. Crystal-field levels and site symmetries of Eu 3+ at the two sites have also been determined.